Acquired Disorder of Platelet Function Associated with Autoantibodies against Membrane Glycoprotein IIb-IIIa Complex - 1. Glycoprotein Analysis

A patient with idiopathic thrombocytopenic purpura developed after splenectomy a thrombasthenia-like severe haemor-rhagic diathesis characterized by a normal or subnormal platelet count, prolonged bleeding time, strongly reduced platelet adhesion to glass and defective platelet aggregation in response to ADP and collagen. In contrast to hereditary thrombasthenia membrane glycoproteins (GP) lib and Ilia were normally present in the patient’s platelets. Immunoelectrophoretic analysis revealed an abnormal behaviour of the patient’s GP IIb-IIIa complex. Autoantibodies against GP IIb-IIIa were detected in Triton-extracted washed platelets. Incubation of normal platelets with plasma from the patient resulted in a similar immunoelectrophoretic abnormality of the GP IIb-IIIa complex indicating that bound autoantibodies (IgG) are responsible for the abnormal immunoelectrophoretic behaviour of the patient’s GP IIb-IIIa complex. Platelet fibrinogen was severely reduced similar to classical thrombasthenia suggesting that the GP IIb-IIIa complex is involved in platelet fibrinogen storage.

[Therapy of inherited diseases of platelet function. Interdisciplinary S2K guideline of the Permanent Paediatric Committee of the Society of Thrombosis and Haemostasis Research (GTH e. V.)]

Inherited disorders of platelet function are a heterogeneous group. For optimal prevention and management of bleeding, classification and diagnosis of the underlying defect are highly recommended. An interdisciplinary guideline for a diagnostic approach has been published (AWMF # 086-003 S2K; Hämostaseologie 2014; 34: 201-212). Underlying platelet disorder, platelet count, age and clinical situation modify treatment. Exclusive transfusion of platelet concentrates may be inappropriate as potentially adverse effects can outweigh its benefit. A stepwise and individually adjusted approach for restitution and maintenance of haemostasis is recommended. Administration of antifibrinolytics is generally endorsed, but is of particular use in Quebec disease. Restricted to older children, desmopressin is favourable in storage pool disease and unclassified platelet disorders. Although licensed only for patients with Glanzmann thrombasthenia and alloantibodies, in clinical practice rFVIIa is widely used in inherited platelet disorders with severe bleeding tendency. This guideline aims at presenting the best available advice for the management of patients with inherited platelet function disorders.

Pharmacokinetic properties of two different recombinant activated factor VII formulations

Recombinant factor VIIa is indicated for treatment of bleeding episodes in patients with haemophilia A or B with inhibitors; in FVII deficiency and in Glanzmann's thrombasthenia. The aim of the study reported here was to compare the pharmacokinetic profiles between two formulations of rFVIIa that are produced in two different cell lines and media: Chinese hamster ovary cells cultured in a serum-free medium (CHO-rFVIIa) and baby hamster kidney cells cultured in a non-human serum-based medium (BHK-rFVIIa). Two clinical trials were performed; one in healthy subjects and the other in patients with congenital haemophilia A or B, with or without inhibitors. Subjects were recruited into a two-way crossover trial and were randomized to receive a dose of CHO-rFVIIa and BHK-rFVIIa. Healthy subjects received one dose of 90 μg CHO-rFVIIa kg(-1) bodyweight (bw) in the newly developed room-temperature stable rFVIIa formulation and one dose of 90 μg BHK-rFVIIa kg(-1) bw, in the original rFVIIa formulation. Patients with haemophilia received one dose of 270 μg CHO-rFVIIa kg(-1) and one dose of 270 μg BHK-rFVIIa kg(-1), both in the room-temperature stable formulation. The trials showed higher FVII activity levels [higher area under the plasma concentration-time curve (AUC)] following administration of CHO-rFVIIa than after BHK-rFVIIa. Therefore, bioequivalence could not be established. The difference in FVII activity levels is believed to be a result of different glycosylation patterns between the two products. Neither the use of CHO-rFVIIa nor the use of one single dose of 270 μg kg(-1) of the newly developed room-temperature stable rFVIIa raised any safety concerns.

[Congenital thrombocytopathies]

Inherited thrombocytopathies are much less frequent in comparison to acquired platelet function disorders. However, congenital disorders can lead to severe bleeding tendency and are often not diagnosed. They are induced by different platelet defects based on disorders of platelet adhesion, receptors, secretion and signal transduction. In some cases they are associated with thrombocytopenia, giant platelets and various comorbidities. This article gives an overview regarding diverse defects, their diagnosis and treatment options.

[Bleeding complications due to anticoagulatoric therapy]

Anticoagulation is a standard treatment in patients with thrombosis and commonly used in surgical procedures for primary thrombosis prophylaxis. The occurrence of bleeding episodes is the predominant treatment complication. Although monitoring of hemostatic parameters reduces the risk of bleeding, bleedings occur in approximately 10% of patients. Besides standard life saving procedures it is crucial to ensure sufficient coagulation by administering factor concentrates (e.g. fresh frozen plasma, prothrombin complex, recombinant factor VIIa), platelet concentrates and fluid. Specific antidotes are not available for the majority of anticoagulant agents.

Platelet-dependent thrombin generation assay for monitoring the efficacy of recombinant Factor VIIa

Although the administration of recombinant coagulation factor VIIa (rFVIIa) is a well established treatment in haemophilia with inhibitory antibodies, monitoring the therapeutic efficacy is still a problem. This is because the complete haemostatic effect in vivo depends on negatively charged surfaces provided by exposed lipids from activated platelets which are not present in standard clinical assays using plasma. The thrombin generation assay, however, measures the endogenous thrombin potential (ETP) in platelet-rich plasma (PRP) and this assay might be useful for monitoring the haemostatic response to rFVIIa. We characterized the in vitro concentration-response relationship of rFVIIa and the thrombin generation parameters ETP, PEAK and TIME TO PEAK using platelet-rich plasma (PRP) and rFVIIa at concentrations between one and five times the therapeutic dose. We also studied the effect of inhibiting tissue-factor and the intrinsic coagulation pathway using excess TF-neutralizing antibodies and corn trypsin inhibitor (CTI), respectively. There was a sigmoid relationship between ETP and PEAK and the dose of rFVIIa. Increasing rFVIIa concentrations between 100 and 500 U/ml resulted in a progressive increase in ETP, whereas supratherapeutical concentrations led to a plateau phase. The plateau phase differed between patients, suggesting a biological variation in the maximum ETP. Neutralization of plasma TF with TF-Ab partially decreased FVIIa efficacy. The inhibitory effect of CTI on rFVIIa-induced thrombin generation via the intrinsic pathway was negligible. The thrombin generation assay using PRP is a useful test for determining the sufficient efficacy of rFVIIa in blood. Once a plateau level is reached, higher doses of rFVIIa have no additional effect on haemostatic efficacy. The variation in plateau levels between subjects indicates that there are inter-individual differences in the level of thrombin activity that can be generated. High doses of rFVIIa are effective even in the absence of TF.

Platelet-dependent coagulation assays for factor VIII efficacy measurement after substitution therapy in patients with haemophilia A

FVIII therapy for haemophilia A is safe and effective, with the problem of individually sufficient efficacy unsettled. Routine one-stage clotting assays and tests employing chromogenic substrates poorly detect individual haemostatic effects of FVIII due to artificial test conditions. In particular, the use of cell-free and diluted plasma samples neglect the crucial role of platelets for thrombin and fibrin formation. To optimize FVIII substitution therapy, we measured in 40 patients with severe to mild haemophilia A before and after FVIII substitution the FVIII activity in cell-free plasma samples using a one-stage clotting assay as well a chromogenic substrate assay and compared the data with those obtained with cell-based coagulation tests, i.e. thrombin generation in platelet-rich plasma (PRP) and thromboelastography (TEG) in samples of citrated whole blood (WB). To determine the maximum ex vivo haemostatic effect we added 1 unit/ml of FVIII to samples of PRP and WB and measured the maximum thrombin generation in the thrombin generation test (TGT) and the maximum clot firmness (MCF) in TEG. After FVIII substitution we observed a nearly linear relation between the individual FVIII activities administered to the patients and the activities measured in the plasma samples. However, data obtained with TGT and TEG revealed a high inter-individual variation and a very poor correlation to the administered FVIII activity. Actually, it could be shown that FVIII substitution yielding in a FVIII plasma activity of about 30% is sufficient to get an ex vivo haemostatic effect of more that 90% as measured by maximum thrombin generation and MCF. FVIII substitution up to a plasma activity of more than 90% did not further enhance the haemostatic effect. Our data clearly demonstrate that the haemostatic effect of FVIII is not only dependent on the activity that is measured in plasma but also depends on the interplay between coagulation and blood cells, in particular with platelets. The use of cell-based coagulation tests such us TGT or TEG may help to optimize FVIII therapy by determining the individual FVIII dosage that produces a maximum haemostatic effect.

Thrombin-induced interleukin 1beta synthesis in platelet suspensions: impact of contaminating leukocytes

A controversial discussion as to whether human platelets are capable of regulated protein synthesis has been ongoing for over half a century. A previous study has suggested that human platelets synthesize large amounts of interleukin 1beta (IL-1beta) in response to external cues and in a physiologically significant manner. However, cytokines such as IL-1beta are generally considered to be products of leukocytes and it could not be completely excluded that contaminating leukocytes may have contributed to the IL-1beta results in platelet preparations. It was therefore our intention to investigate whether residual leukocytes had an impact on thrombin-induced IL-1beta synthesis. Using various methods to reduce the level of contaminating leukocytes, we found that IL-1beta production in platelet-rich suspensions is dependent on the presence of leukocytes, as it was decreased by reducing the number of leukocytes. In addition, we found that thrombin-induced IL-1beta synthesis was completely eliminated in leukocyte-free platelet preparations and could be restored by adding leukocytes. IL-1beta synthesis could be detected in platelet suspensions contaminated with at least 1 leukocyte per 10(5) platelets. This study demonstrated that platelets are incapable of synthesizing detectable amounts of IL-1beta on their own. We suggest that any IL-1beta synthesis detected is a by-product of leukocytes contaminating the platelet preparations. Thus, the hypothesis that platelets producing IL-1beta, provide a new link between thrombosis and inflammation needs to be reconsidered.

Klinische Bewertung potentieller Einsatzbereiche von rekombinantem Faktor VIIa bei internistischen und pädiatrischen Erkrankungen

Recombinant factor VIIa (rFVIIa) is increasingly used outside the labeled indications for treatment of life-threatening bleeding episodes after failure of the respective standard therapy. An interdisciplinary group of experts summarizes the state of knowledge of the use of rFVIIa in gastroenterology and hepatology, thrombocytopenia and -pathia, coagulation factor deficiencies, von Willebrand's disease, periinterventional bleeding without specific bleeding diathesis, drug-induced bleeding, disseminated intravascular coagulation, and neonatology. The most commonly used dose is 90 microg/kg body weight rFVIIa as bolus, if necessary followed by additional injections at intervals of 2-3 h. In factor VII deficiency lower dosages of 15-30 microg/kg body weight of rFVIIa are given every 4-6 h, whereas higher doses of 150-200 microg/kg body weight are used in neonates.

Effect of Dealcoholized Beer (Bitburger Drive®) Consumption on Hemostasis in Humans

BACKGROUND

The beneficial effect of moderate alcohol consumption in lowering the risk of cardiovascular disease has been shown in several epidemiologic studies. Such studies have also shown, however, that the protective effect of alcoholic beverages like wine and beer is not only due to the ethanol content but also to the presence of nonalcoholic constituents. The positive effect of alcoholic beverages has been attributed to changes in lipoprotein metabolism, but there is substantial evidence that effects on hemostasis play an important role. Whether the effects of alcoholic beverages on hemostasis are due exclusively to ethanol or are due, in part, to nonalcoholic components, is still under debate.

METHODS

We have examined the hemostatic effects of 3 liters of beer, dealcoholized beer, and ethanol/water (v/v 4%), consumed over a period of 3 hr, in 12 young healthy volunteers. Platelet parameters CD62, PAC-1, and monocyte platelet aggregates were analyzed using flow cytometric measurements. The activity of factor VII was determined with a prothrombin time (PT) assay and plasminogen activator inhibitor activity using a chromogenic substrate. Thrombin generation was determined according to the method of Hemker.

RESULTS

All three fluids administered, dealcoholized beer, beer, and ethanol, reduced the expression of activated fibrinogen receptor, the platelet activation marker CD62, and the formation of monocyte-platelet-aggregate. In addition, dealcoholized beer also showed significant inhibitory effects on thrombin generation, whereas beer and ethanol showed procoagulatory effects.

CONCLUSIONS

This study has shown that the acute consumption of dealcoholized beer inhibits thrombogenic activity in young adults. This action could have a beneficial effect on the development of coronary artery disease. Thus, the consumption of dealcoholized beer could provide cardiovascular benefit without the negative effects of alcohol.

Glanzmann thrombasthenia Frankfurt I is associated with a point mutation Thr176Ile in the N-terminal region of alpha IIb subunit integrin

In this study, we report on the characterization of a patient with Glanzmann thrombasthenia (GT). Immunochemical analysis on platelets from the patient showed that the expression of alpha IIb beta 3 was only 25% of that in normal healthy controls, suggesting a case of GT. Functional analysis revealed a total lack of fibrinogen binding capacity. Molecular genetic analysis of the full-length cDNA sequences of alpha IIb and beta 3 subunits showed a novel point mutation C621T in alpha IIb cDNA, leading to a missense substitution of threonine for isoleucine at position 176. Coexpression of normal beta 3 and mutant alpha IIb(1176) isoform in mammalian cells showed a marked reduction in the expression of alpha IIb beta 3 heterodimer when compared to the wild-type and a decreased intracellular level of alpha IIb. The T176 I mutation is located in the N-terminal region in the W3:1-2 connecting strand of the beta-propeller. These data suggest that the N-terminal alpha IIb domain plays an important structural role in the formation of heterodimer and that it is also involved in fibrinogen binding.

Pharmacodynamic characterization of the interaction between the glycoprotein IIb/IIIa inhibitor YM337 and unfractionated heparin and aspirin in humans

AIMS

To investigate the pharmacodynamic interaction of unfractionated heparin (UFH) and acetylic salicylic acid (ASA) on YM337, a monoclonal humanized antibody of the platelet GPIIb/IIIa receptor.

METHODS

In a randomized, placebo-controlled study three treatment groups each with six healthy volunteers received the following medication: group 1, ASA (3 days) + UFH + YM337 (placebo); group 2, ASA (placebo) + UFH (placebo) + YM337; group 3, ASA + UFH + YM337. Assessments were made over 24 h and included bleeding time (BT), ADP (20 microm)- and collagen (5 microg ml-1)-induced platelet aggregation and PAC1 and CD62 expression measured by flow cytometry.

RESULTS

In group 3 BT was prolonged to 35 [median, 16-45 min (1,3 quartile)] after UFH administration, increasing to 45 [median, 42-45 min (1,3 quartile)] after YM infusion (6 h). BT remained elevated to 26 [median, 14-45 min (1,3 quartile)] at 24 h, while groups 1 and 2 returned to normal values. Collagen-induced aggregation was 73% [median, 70-80% (1,3 quartile)] under YM337 alone, 79% [median, 72-80% (1,3 quartile)] under ASA + UFH and reduced only in group 3 to 24% [median, 18-29% (1,3 quartile)]. In both groups receiving active YM337, PAC1 expression showed a reduction to < 20% after 6 h of infusion. CD62 expression was not significantly affected by any treatment.

CONCLUSION

UFH and YM337 have strong synergistic effects on BT, while coadministration of ASA strongly augments inhibitory effects of YM337 on collagen-induced platelet aggregation.

Close relationship between the platelet activation marker CD62 and the granular release of platelet-derived growth factor

The expression of CD62 on the surface of platelets is considered to be an indicator of platelet degranulation and secretion. We characterized the relationship between CD62 expression and platelet-derived growth factor (PDGF)(AB) and PDGF(BB) secretion in response to thrombin-receptor activating peptide (TRAP). The principal findings were 1) expression of CD62 as a constituent of platelet alpha-granule membrane and secretion of PDGF, an important ingredient of alpha-granules, can be stimulated by TRAP-induced activation in a dose-dependent fashion; 2) the activation marker and secretion product are closely correlated with each other; and 3) changes in the CD62 expression induced by a drug, namely clopidogrel, or by a disease, namely diabetes, are paralleled by changes in PDGF secretion. Although CD62 is perceived as an activation marker of platelets indicating enhanced aggregability and secretion of alpha-granular content, the proof that the CD62 status and its modifications reflect directly the actual secretion of the most important platelet mitogen, PDGF, has so far not been given. This ex vivo-in vitro study shows that at least for the activation pathway provided by the PAR-1 receptor for which TRAP is the selective agonist, CD62 expression on platelets could be a surrogate for their secretory activity.

Reduction in thrombus extension and clinical end points in patients after initial treatment for deep vein thrombosis with the fixed-dose body weight-independent low molecular weight heparin certoparin

Low molecular weight heparin (LMWH) is effective in the treatment of acute deep vein thrombosis (DVT) in adults. This has not been demonstrated for one LMWH alone. The relationship between venographic changes due to LMWH therapy and clinical outcome in the initial treatment period has not been reported. A pooled analysis of two clinical trials was performed. The trials compared a fixed-dose, body weight-independent, subcutaneous LMWH, certoparin (8000 antifactor Xa [aXa] U twice a day [b.i.d.]), with an adjusted-dose intravenous unfractionated heparin (UFH) with respect to venographic changes expressed as Marder score and occurrence of recurrent venous thromboembolism, major bleeding, and mortality. The Marder score was 23.2 +/- 8.4 in patients randomized to LMWH (n = 299 paired phlebograms) and 23.9 +/- 8.9 in patients allocated to UFH (n = 297 paired phlebograms) at entry (2p = 0.23) and 18.9 +/- 9.7 and 20.5 +/- 9.9 at the end of the initial therapy (2p = 0.04), respectively. The composite outcome of recurrent venous thromboembolism, major bleeding, and mortality occurred less frequently during treatment with LMWH (n = 393) than it did with UFH (n = 404, 1.3% versus 5.0%, risk reduction [RR] 0.26, 95% confidence interval [CI] 0.11 to 0.63, 2p = 0.004). Single events of recurrent thromboembolism (2p = 0.12), major bleeding (2p = 0.03), and mortality (2p = 0.12) were observed less frequently with LMWH. A trend toward a lack of regression of thrombus size was observed in recurrent venous thromboembolism (2p = 0.08). Body weight-independent LMWH significantly reduces thrombus size and the incidence of composite outcome during the initial treatment of acute proximal venous thrombosis compared with adjusted dose intravenous UFH. The data indicate a relation between an unimproved Marder score and a recurrent venous thromboembolism.

Thrombin causes vascular endothelial growth factor expression in vascular smooth muscle cells: role of reactive oxygen species

Vascular endothelial growth factor (VEGF) has been implicated in the reendothelialization of the vascular wall after balloon injury. This study investigated whether thrombin, which is formed during activation of the coagulation cascade at sites of vascular injury, upregulates VEGF expression in vascular smooth muscle cells (VSMCs). VEGF expression was assessed in native and cultured VSMCs by Northern blot analysis and reverse transcription-polymerase chain reaction and the release of VEGF protein by immunoassay. alpha-Thrombin time- and concentration-dependently increased VEGF mRNA levels, mainly that mRNA coding for the soluble splice variant VEGF(164/165), and stimulated the release of VEGF protein. These effects required the proteolytic activity of thrombin and were mimicked by a thrombin receptor activating-peptide. Upregulation of VEGF expression was also induced by conditioned medium from alpha-thrombin-stimulated VSMCs. Both the early and the delayed alpha-thrombin-induced VEGF expressions were attenuated by antioxidants and by diphenyleneiodonium. alpha-Thrombin-induced VEGF release was significantly reduced by a platelet-derived growth factor (PDGF)-, a transforming growth factor (TGF)-beta-, and a basic fibroblast growth factor (bFGF)-neutralizing antibody. Thrombin caused a redox-sensitive upregulation of expression of VEGF in VSMCs through a direct and an indirect effect, which was dependent on the endogenous formation of PDGF, TGF-beta, and bFGF. Upregulation of VEGF expression may represent an important mechanism by which the coagulation cascade contributes to the regeneration of the endothelial lining at sites of balloon injury.

Pharmacodynamic characterization of the interaction between abciximab or tirofiban with unfractionated or a low molecular weight heparin in healthy subjects

AIMS

The objective of our study was to define the interaction between either unfractionated heparin (UFH) or a low molecular weight heparin, reviparin (REV), and the pharmacodynamic profile of the GPIIb/IIIa-antagonists abciximab (ABC) or tirofiban (T).

METHODS

Two studies each containing 18 healthy subjects were performed, and all were pretreated with aspirin (ASA) for 3 days. Volunteers then received UFH (5000 IU bolus/infusion 7 IU kg(-1) h(-1) for 7 h, n = 6), REV (4200-anti-Xa-IU s.c., n = 6) or placebo (n = 6). One hour later, ABC (study I) or T (study II) were given by i.v. infusion for 6 h. The pharmacodynamic effects measured were bleeding time (BT), fibrinogen-binding at the GPIIb/IIIa-receptor (FIB), expression of the platelet secretion marker CD62, and ADP (20 microM)- and collagen (5 microg ml(-1))-induced platelet aggregation.

RESULTS

After treatment with both GPIIb/IIIa-antagonists, prolongation of BT occurred to a similar magnitude (approximately 25-30 min) and was not affected by UFH or REV-comedication. ABC or T with ASA alone resulted in nearly the same magnitude of reduction in FIB and platelet aggregation. After coadministration with UFH, FIB was significantly higher (thus less inhibited) than after after T + ASA alone (19 +/- 16% vs 55 +/- 36%) or ABC + ASA alone (8 +/- 9% vs 32 +/- 11%). This attenuation of FIB was not seen with REV. Inhibition of ADP-and collagen-induced aggregation tended to be attenuated by treatment with UFH (e.g. ADP-induced aggregation at 0.25 h after ABC + ASA alone =13 +/- 4%; after coadministration with UFH = 40 +/- 26%). No such changes were noted with REV. Minor reductions in CD62-expression were seen in subjects given ABC or T alone, but expression was not affected by UFH or REV.

CONCLUSIONS

Co-medication with UFH attenuated platelet inhibition during treatment with GPIIb/IIIa-antagonists, but these effects were not seen with the low molecular weight heparin reviparin. The results show that administration of reviparin together with abciximab or tirofiban did not adversely affect the pharmacodynamic profile of these GPIIb/IIIa-antagonists.

In vitro dose response to different GPIIb/IIIa-antagonists: inter-laboratory comparison of various platelet function tests

AIMS

The aim of this study was to assess the inter- and intra-laboratory variation of the concentration-response to the GPIIb/IIIa-antagonists abciximab and eptifibatide on platelet aggregometry and to compare results with flow cytometric tests as well as the rapid platelet function analyser (RPFA).

METHODS

In five different laboratory sites, blood from three to five healthy donors was spiked with abciximab or eptifibatide, followed by the assessment of: (1) aggregometry (anticoagulant: sodium citrate 3.18% or hirudin 5 microg/ml); (2) flow cytometry (fibrinogen binding or PAC1-expression), or (3) RPFA. Dose-response curves were established on the basis of a sigmoidal Imax)-model [I=(Imax)*Cg)/(IC50g + Cg)].

RESULTS

For citrated blood, aggregation induced by 20 microM ADP was blocked up to 100% by both GPIIb/IIIa-antagonists, IC50 values varied between 0.11-0.22 microg/ml for eptifibatide and 1.25-2.3 microg/ml for abciximab. I(max) of the response to 5 microg/ml collagen ranged from 46% to 100%, and IC50 values varied between 0.28-0.34 microg/ml for eptifibatide and 2.3-3.8 microg/ml for abciximab. In hirudinized blood, IC50 values for eptifibatide were 1.5- to 3-fold higher than those obtained with citrated plasma. Inhibition of PAC1-expression by abciximab (IC50) 0.84 microg/ml) showed results similar those of the RPFA (approx. 1.0 microg/ml); larger differences between PAC1 and RPFA results were observed for eptifibatide. Based on aggregometry, eptifibatide concentrations for 80% inhibition varied from 0.27 to 0.55 microg/ml, and were considerably less when the RPFA was taken as basis (0.15 or 0.22 microg/ml). A similar pattern was observed for abciximab.

CONCLUSIONS

We found quite a low inter- and intra-laboratory variation in the in vitro pharmacodynamic characterization of GPIIb/IIIa-antagonists by aggregometry, making results of these tests obtained from different laboratories during clinical trials at least comparable. The RPFA exhibits a higher sensitivity to inhibitory GPIIb/IIIa-effects, in keeping with the "real" inhibition of the activated receptor (PAC1) as assessed with more elaborate flow cytometry.

Platelet glycoprotein expression in patients with myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are characterized by a haematopoetic insufficiency that can lead to acute leukemia. A multistep pathogenesis caused by a clonal stem cell defect affecting several differentiation pathways has been proposed for MDS. Contrary to the better characterized alteration of lymphoid and myeloid differentiation, defects in thrombocytopoesis in MDS remain less clear. In the present study, we analyzed the expression of platelet glycoprotein (GP) Ia/IIa, IIb/IIIa, Ib/IX, and IV in 21 MDS patients (12 RA, 2 RARS, 4 RAEB, 1 RAEB-T, 2 CMML) and healthy controls by flowcytometric analysis and quantitation of platelet GP RNA using fluorescence-based PCR. We observed a reduced cell surface expression of GPIb (p<0.01) and GPIIb/IIIa (p<0.01), while GPIa/IIa and GPIV expression was only marginally different between patients and controls. In contrast, there was a two-fold increase of platelet GPIb and GPIIb RNA and a three-fold increase of GPIV RNA among MDS patients. Increased levels of platelet GPIb and GPIIb RNA were significantly more prominent among patients with RAEB(-T)/CMML (p<0. 05) in comparison to patients with RA/RARS. In conclusion, we demonstrate alterations in the cell surface expression and RNA content of platelet GPs in MDS patients. These data are consistent with dysmegakaryocytopoiesis and a defect in thrombocytopoiesis among MDS patients resulting from the clonal stem cell defect in MDS.

Oxidative stress and expression of p22phox are involved in the up-regulation of tissue factor in vascular smooth muscle cells in response to activated platelets

Vascular injury after balloon angioplasty results in the rapid activation of platelets leading to the release of growth factors and vasoactive substances. In addition, up-regulation of tissue factor (TF) and an increased production of reactive oxygen species (ROS) have been detected at sites of vascular injury. We investigated whether platelet-derived products (PDP) released from activated human platelets increase ROS production, resulting in the induction of TF expression in vascular smooth muscle cells (SMC). PDP induced a time- and concentration-dependent increase in ROS generation in cultured SMC that was mediated mainly by PDGF-AB and TGF-beta1 and impaired by the flavin inhibitor diphenylene iodonium. Increased ROS formation was associated with enhanced mRNA levels of the small NAD(P)H oxidase subunit p22phox or its smooth muscle isoform. Transient transfection with a p22phox antisense vector decreased PDP-induced ROS generation. PDP up-regulated TF mRNA expression, which was redox sensitive and reduced by transfection of the p22phox antisense vector. In addition, PDP-stimulated reporter gene activity of two TF promoter constructs was decreased by coexpression of the p22phox antisense vector. These results indicate that activated platelets up-regulate TF expression and that this response involves ROS generation and a p22phox-containing NAD(P)H oxidase in SMC.

Ex vivo--in vitro interaction between aspirin, clopidogrel, and the glycoprotein IIb/IIIa inhibitors abciximab and SR121566A

OBJECTIVES

To assess the interaction between aspirin and clopidogrel in healthy male volunteers and the interaction of the glycoprotein IIb/IIIa (GPIIb/IIIa) inhibitors abciximab and SR121566A with blood from those pretreated subjects (ex vivo-in vitro).

METHODS

Aspirin (300 mg/day), clopidogrel (75 mg/day), or the combination of both drugs were administered orally for 8 days. Group 1 (n = 5) started with aspirin and group 2 (n = 5) with clopidogrel. From day 4 to day 8, subjects of both groups received the combined treatment. Blood from these subjects was spiked with abciximab (0.5 and 1.5 microg x mL(-1)) and SR121566A (31 and 62 ng x mL(-1)).

RESULTS

In vivo, average bleeding times were 6.8 minutes at baseline, 20.3 minutes for clopidogrel alone (P < .01), 10.9 minutes for aspirin alone (difference not significant), and 24.0 minutes (P < .01) for the combined treatment. Fibrinogen binding to the platelet GPIIb/IIIa receptor was reduced for aspirin to 69% (difference not significant), to 63% for clopidogrel (difference not significant), and to 63% for the clopidogrel plus aspirin combination (P < .01). CD62 expression as a marker of platelet granular secretion was reduced to 66% by clopidogrel (P < .01) and to 41% by the combination of clopidogrel and aspirin; aspirin alone had no effect. In vitro, with pretreatment with aspirin and clopidogrel, inhibitory effects of the GPIIb/IIIa inhibitors on fibrinogen binding were additive to changes observed with aspirin or clopidogrel alone. No effect on CD62 expression was observed with either GPIIb/IIIa inhibitor. Aspirin and clopidogrel reinforced effects of the GPIIb/IIIa inhibitors on adenosine diphosphate (5 micromol/L)-induced aggregation in an additive manner, a supra-additive effect was observed with collagen (2 microg x mL(-1))-induced aggregation.

CONCLUSION

The augmentation of the antiaggregatory effects of GPIIb/IIIa inhibitors by aspirin and clopidogrel and the lack of antisecretory effects of GPIIb/IIIa inhibitors may favor their combination with clopidogrel.

Differential in vitro effects of the platelet glycoprotein IIb/IIIa inhibitors abixicimab or SR121566A on platelet aggregation, fibrinogen binding and platelet secretory parameters

The aim of this study was to compare fibrinogen binding, inhibition of platelet aggregation and secretory potential of the MAb abciximab (0.5-5 microg/mL) and the peptidomimetic compound SR121566A (15-250 ng/mL) in vitro in whole blood. Fibrinogen binding was followed by flow cytometry; platelet function was evaluated by light transmittance and by impedance aggregometry. Secretory functions of platelets were evaluated using ATP as marker for early secretion by dense granulae and P-selectin (CD62) for alpha-granular secretion as well as CD63 for lysosomal degranulation. Results showed that fibrinogen binding induced by 5 microM TRAP was maximally inhibited greater than 80% at 3 microg/mL abciximab or at 250 ng/mL SR121566A. At these concentrations of antagonists, platelet aggregation induced by 5 microM ADP or 2 microg/mL collagen was inhibited completely. Expression of CD62 was reduced 34% with abciximab or 15% with SR121566A; CD63 expression was reduced 22% with both agents. With both agents, the EC50 for inhibition of CD62 and CD63 expressions was in similar magnitudes than the EC50 for fibrinogen binding inhibition. With 3 microg/mL abciximab, ATP secretion was maximally reduced to 50% of the control, whereas SR121566A at 250 ng/mL had no inhibitory effect on this parameter. A slight increase in ATP secretion was seen with 0.5 microg/mL abciximab and with SR121566A in concentrations of less than 45 ng/mL. The data suggest a discoupling between the anti-aggregatory and the antisecretory effects of IIb/IIIa antagonists. Because it is not established to what extend CD62 or CD63 expression can be reduced by any means, the reduction by 20-30% obtained by 3 microg/mL abciximab or 250 ng/mL SR121566A might already be the maximum possible inhibition by these agents.

Preclinical biochemistry and pharmacology of low molecular weight heparins in vivo--studies of venous and arterial thrombosis

Low molecular weight heparins (LMWHs) are effective agents in both venous and arterial thrombosis. Extensive preclinical studies in various animal models show that there are substantial differences in antithrombotic efficacy between LMWHs, and that the relative efficacy of individual agents depends on the thrombogenic stimulus used. Relative efficacy cannot be predicted on the basis of molecular weight, nor on the basis of anti-factor Xa or anti-factor IIa potency. This suggests that other mechanisms of action, e.g., the release of tissue factor pathway inhibitor (which differs among the LMWHs), are important. Data obtained with a specific LMWH cannot be extrapolated to other compounds within the same class and their substitution in the clinical setting is, therefore, inappropriate.

Pharmacokinetics and pharmacodynamic effects of a new antibody glycoprotein IIb/IIIa inhibitor (YM337) in healthy subjects

BACKGROUND

This study describes the first administration of YM337, the Fab fragment of a humanized monoclonal antibody against the fibrinogen GP IIb/IIIa receptor, in healthy male humans.

METHODS AND RESULTS

Platelet aggregation (20 micromol/L ADP), platelet adhesion, fibrinogen binding, bleeding time, and YM337 concentrations in plasma were studied in substudy 1 after single boluses of 0.025, 0. 05, 0.1, 0.2, and 0.4 mg/kg YM337 and in substudy 2 after a bolus (0. 35 mg/kg) plus 6 hours of infusion at different dose levels of YM337 (0.5, 0.75, 1.0, 1.5 microg. kg(-1) x min(-1)), with abciximab as reference drug (n=5 or 6 subjects per group). After the 0.2-mg/kg and 0.4-mg/kg boluses, fibrinogen binding was reduced by >80% and bleeding time was prolonged to approximately 60 minutes. Bolus followed by infusion of 1.0 and 1.5 microg x kg(-1) x min(-1) YM337 maintained inhibition of platelet aggregation >80%. Aggregation and bleeding time returned to normal within 24 hours. A bolus of 0.25 mg/kg of abciximab followed by an infusion of 0.125 microg x kg(-1) x min(-1) showed effects similar to those observed with the 0.5- and 0. 75-microg x kg(-1) x min(-1) infusion of YM337. In 53 subjects exposed to YM337, 1 case of transient thrombocytopenia and 3 minor bleeding events occurred. No human anti-chimeric antibodies were detected 2 weeks and 2 months after administration.

CONCLUSIONS

YM337 effectively inhibits IIb/IIIa-mediated platelet aggregation and adhesion in humans. The results of this phase 1 study will give rise to further clinical evaluation of YM337.

Aggregating human platelets stimulate expression of vascular endothelial growth factor in cultured vascular smooth muscle cells through a synergistic effect of transforming growth factor-beta(1) and platelet-derived growth factor(AB)

BACKGROUND

Vascular endothelial growth factor (VEGF), an endothelial mitogen and chemoattractant, has been implicated in the recovery of the endothelium after balloon injury. The increased expression of VEGF in vascular smooth muscle cells (SMC) at sites of injury suggests that this cell type may be a major cellular source of VEGF. This study examined whether aggregating platelets stimulate VEGF expression in cultured SMC.

METHODS AND RESULTS

++VEGF expression in SMC was assessed by Northern blot analysis and by reverse transcription followed by polymerase chain reaction and the release of VEGF by Western blot analysis and immunoassay. Platelet-derived products (PDP) released by aggregating human platelets time-dependently and concentration-dependently enhanced VEGF mRNA levels, mainly that coding for the soluble splice variant VEGF(165/164), and stimulated the release of VEGF protein. These effects were potentiated by transient acidification of PDP, which release bioactive transforming growth factor (TGF)-beta(1), and mimicked by platelet-derived growth factor (PDGF)(AB) and TGF-beta(1) in a synergistic manner. Both a TGF-beta-neutralizing antibody and a PDGF-neutralizing antibody significantly attenuated the effect of acidified PDP on VEGF production.

CONCLUSIONS

Aggregating human platelets induce VEGF mRNA expression in cultured SMC and the subsequent release of VEGF protein. This effect can be attributed to a supra-additive action of PDGF(AB) and TGF-beta(1) and may represent a novel mechanism by which platelets contribute to the recovery of the endothelial lining at sites of balloon-injured arteries.

Spontaneous platelet aggregation as a predictive risk factor for vascular occlusions in healthy volunteers? Results of the HAPARG Study. Haemostatic parameters as risk factors in healthy volunteers

The HAPARG Study (haemostatic parameters as risk factors in healthy volunteers) was performed in a subset of volunteers taking part in the MARISK Study (Mainzer Risikoindikatoren Studie für die koronare Herzkrankheit) sponsored by the German Ministry of Research and started in 1984. A previous study (Yamanishi et al., Thromb Haemostas 1985;54:539-543) had shown that spontaneously enhanced platelet aggregation as measured with the PAT-III-test and higher fibrinogen concentrations are significant risk factors for new vascular occlusions in diabetic patients. It was the aim of the HAPARG Study to establish whether spontaneous platelet aggregation and other hemostatic variables are independent risk factors for vascular occlusions in healthy volunteers. Employees of a chemical/pharmaceutical company aged 40-65 years and personnel of the University of Mainz, aged 30-60 years were included in this prospective study. Besides anamnestic data such as on smoking, hypertension and diabetes, blood pressure, the ankle/arm Doppler-index and an ECG were recorded and serum cholesterol, HDL, LDL, triglycerides, uric acid and glucose were measured. Men (1884) and women (989) entered the study and were followed for 4-6 years. In the age group of 30-50 years, more women than men were included. During the observation period 53 vascular occlusions occurred (36 coronary and nine cerebral events and eight peripheral vascular occlusions). Only three of these endpoints occurred in women. Besides age (odds ratio = 1.7, P = 0.02) and gender as expected risk factors, the multivariate logistic stepwise regression analysis revealed smoking (odds ratio = 2.2, P = 0.008), lower HDL-levels (odds ratio = 2.2, P = 0.013), elevated diastolic blood pressure (odds ratio = 1.4. P = 0.004) followed by spontaneous platelet aggregation (odds ratio = 1.1, P = 0.037), and slightly elevated blood glucose (P = 0.0047) as significant risk factors for men. Higher fibrinogen levels missed significance in this analysis (P = 0.059). None of the other hemostatic parameters showed a significant correlation with the vascular events. To our knowledge, this has been the first prospective trial in a large population of healthy individuals in which a platelet function parameter has been studied together with other possible risk factors. Spontaneously enhanced platelet aggregation is probably an independent risk factor and, like elevated fibrinogen and other haemostatic variables, an indicator of an ongoing active atherosclerotic process.

Efficacy of a low molecular weight heparin administered intravenously or subcutaneously in comparison with intravenous unfractionated heparin in the treatment of deep venous thrombosis. Certoparin-Study Group

BACKGROUND

The main objective of the study presented was to test if thrombus regression can be improved by treatment with an intravenously or subcutaneously administered low molecular weight heparin (LMWH). Patients with acute deep vein thrombosis were randomly assigned to receive either intravenous UFH (131 patients), intravenous (i.v.) LMWH (128 patients), or 8000 IU of the same LMWH bid subcutaneously (s.c.) (128 patients). All patients were treated with heparin for 14 to 16 days. Vitamin-K-antagonist prophylaxis was started between Day 12 and Day 14 after enrollment into the study.

METHODS

Phlebographies and perfusion/ventilation lung scans were performed at baseline and on Days 12 to 16. Primary endpoint of the study was a reduction of the phlebographic Marder score. Secondary endpoints were recurrent thrombosis and pulmonary embolism (PE), major and minor bleedings and the rate of PE at inclusion and at the end of the study assessed by ventilation/perfusion scans.

RESULTS

The Marder score improved by at least 30% in 32.4% (95% CI: 22.6 ... 42.2) of the patients receiving UFH, in 34.0% (95% CI: 24.9 ... 44.0) receiving LMWH i.v. and in 42.6% (95% CI: 32.8 ... 52.8) treated with the low molecular weight heparin s.c. The difference between LMWH s.c. and UFH was 10.2% (95% CI: -3.7% ... +24.5%) (p = 0.11). PE with clinical signs confirmed by objective methods occurred in three patients of the UFH group, one of whom died and was not observed in patients of the i.v. or s.c. LMWH-groups. During the first 15 days no patient receiving UFH or i.v. LMWH, and one patient on s.c. LMWH had a recurrent thrombosis. Major bleedings were observed in four patients receiving i.v. UFH compared to nine patients on i.v. LMWH (one of these patients died) and one patient on s.c. LMWH. Perfusion ventilation lung scans were obtained from 287 patients at baseline and from 246 patients on Days 12-16. PE, defined according to PIOPED-criteria as intermediate or high probability scans, was observed in 38.0% of the patients entering the study and in 18.3% on Days 12 to 16. New asymptomatic PE occurred less frequently in the groups on LMWH (7.1%, 7.5%, respectively) than in the UFH-group (12.6%) (not significant).

CONCLUSIONS

S.c. treatment with a LMWH (certoparin) (b.i.d.) is at least as effective as UFH i.v. The hypothesis of increased efficacy of subcutaneous LMWH in resolving venous thrombi will have to be confirmed by an independent study comparing s.c. LMWH with UFH. The i.v. continuous infusion of the LMWH for 12 to 16 days does not result in a higher venous re-opening rate than intravenous standard heparin.

[Prevalence of hepatitis G virus genome in blood donors]

The relevance of the GB virus C/hepatitis G virus (GBV-C/HGV) in blood banking results from its high prevalence in blood donors and the fact that it is present at a very high percentage (18%) in polytransfused and hemophiliac patients. Since there is no assay available for serological testing, we developed a sensitive PCR utilizing newly designed NS3 primers to investigate the prevalence in blood donors in Hessia. Testing 1,143 accepted blood donors with alaninaminotransferase (ALT) concentrations < 45 U/l we found 15 (1.3%) positive for GBV-C/HGV RNA. From 507 donors settling in urban Frankfurt areas, 10 (2.0%) were positive. Of those donors settling in rural hessian areas only 5/635 (0.8%) tested positive. By testing 100 excluded donors with ALT values > 45 U/l, 3% turned out to be positive. In 4 out of 9 recipients of GBV-C/HGV-positive blood products we detected the donor viral RNA as proved by sequencing and phylogenetic analysis. The virus was transmitted to 3 recipients by erythrocytes and to 1 recipient by platelets. Testing family members of the GBV-C/HGV-positive blood donors we could not detect any intrafamilial transmission.

High doses of methylene blue/light treatment crosslink the A-alpha-subunit of fibrinogen: influence of this photooxidization on fibrinogen binding to platelets

Irradiation in the presence of 1 microM methylene blue (MB) inactivates enveloped viruses in human plasma. This method is a useful tool to enhance the safety of human fresh-frozen plasma in blood donor banks. Via a photooxidative mechanism, viral structures as well as plasma proteins, especially fibrinogen, can be damaged. We investigated the effect of MB/light-induced photooxidative modification on the structure of fibrinogen and its function in the interaction with platelets in the concentration range of 150 microM MB. Densitometric scanning of reduced SDS-PAGE showed a decrease in the Aalpha-subunit of fibrinogen as well as an increase in high-molecular-weight (HMW) aggregates with increasing MB concentrations. The HMW aggregates may be due to covalent crosslinking of single Aalpha-subunits via photooxidation induced by MB/light treatment. Fibrinogen treated with high doses of MB (50 microM) showed a weaker binding to the fibrinogen receptor (GP IIb/IIIa) on the platelet surface and a decrease in platelet aggregation after stimulation with ADP and photooxidized fibrinogen. These effects were not detected in fibrinogen isolated from virus-inactivated plasma (1 microM MB). This was in agreement with normal binding of fibrinogen to GP IIb/IIIa on platelets.

Aggregating human platelets stimulate the expression of thrombin receptors in cultured vascular smooth muscle cells via the release of transforming growth factor-beta1 and platelet-derived growth factorAB

BACKGROUND

Thrombin and the thrombin receptor have been implicated in the proliferation of vascular smooth muscle cells (VSMCs) observed after angioplasty and in atherosclerosis. Because thrombin receptor activation is an irreversible proteolytic event, the marked upregulation of the smooth muscle cell thrombin receptor after vascular injury may account for the maintained mitogenic activity of thrombin. The present study was designed to determine whether aggregating platelets stimulate thrombin receptor expression in cultured VSMCs and, if so, to identify the mediators.

METHODS AND RESULTS

Thrombin receptor expression was assessed by Northern and Western blot analyses and functionally by measuring the release of 6-keto prostaglandin F1alpha. Platelet-derived products (PDPs) released by aggregating human platelets enhanced thrombin receptor mRNA levels in a time- and concentration-dependent manner, an effect that was potentiated by transient acidification of PDPs, which release bioactive transforming growth factor (TGF)-beta1, and that was slightly inhibited by ketanserin. Among several factors known to be released by aggregating platelets, only TGF-beta1, platelet-derived growth factorAB (PDGF(AB)), and serotonin mimicked the PDP effect. The level of membrane thrombin receptor protein was increased in TGF-beta1-treated VSMCs. Pretreatment of VSMCs with either acidified PDP, or TGF-beta1 increased the alpha-thrombin-stimulated release of 6-keto prostaglandin F1alpha. This effect was blunted by incubating acidified PDP with either a TGF-beta- or a PDGF-neutralizing antibody.

CONCLUSIONS

Aggregating human platelets stimulate the expression of thrombin receptors in VSMCs through the release of TGF-beta1, PDGF(AB), and, to a lesser extent, serotonin. The upregulation of the thrombin receptor by products released by aggregating platelets may sustain the mitogenic activity of thrombin in the vascular wall at sites of injury.

Analysis of glycoprotein Ia, Ib, IIb and IV RNA in platelets: quantitative determination using fluorescence-based polymerase chain reaction

The aim of this study was to analyze the RNA level of glycoprotein (GP) receptors in platelets. We have therefore established a quantitative fluorescence-based polymerase chain reaction (PCR) to analyze GP Ia, Ib, IIb, and IV RNA. Isolation of platelet RNA was performed by guanidium isothiocyanate/phenol chloroform extraction. An internal standard consisting of cRNA copies from plasmid pAW109 was included before reverse transcription in each RNA sample and PCR amplification was performed using fluorescence-labeled primers. Subsequently, PCR fragments were separated by gel electrophoresis and quantitation of the GP-specific fragments was done by measuring the fluorescence intensities in comparison to the internal standard. Relative amount of GP RNA/platelet were calculated taking into account the number of platelets used for isolation of platelet RNA and the platelet size as determined by flow-cytometric analysis. Using this method we analyzed the GPIa, Ib, IIb and IV RNA content of platelets in healthy blood donors. In parallel experiments the number of GP cell surface receptors was measured by flow-cytometric analysis and correlated with the GP-specific RNA content. This method may be useful to study the GP-specific RNA content in platelets as well as in other tissues, such as megakaryocytes, especially in patients with congenital or acquired platelet function disorders.

Sensitive determination of the RhD genotype in mixed samples using fluorescence-based polymerase chain reaction

OBJECTIVES

Prenatal determination of the fetal RhD status in pregnancies of Rh-negative (Rh-neg) women by polymerase chain reaction (PCR) on DNA has become of increasing importance. Since determination of the RhD genotype in these cases is usually performed in samples containing both maternal Rh-neg and fetal Rh-neg or Rh-positive (Rh-pos) DNA, the sensitivity and specificity of PCR-based DNA detection are of crucial importance in the diagnosis of the fetal RhD status.

METHODS

We developed a method for RhD typing using the PCR and a fluorescence-based detection method that allows us to determine RhD-pos DNA even if it is mixed with large amounts of Rh-neg DNA.

RESULTS

Using this approach, Rh-pos DNA could be detected in dilutions with Rh-neg DNA of as high as 1 in 10,000 (Rh-pos/Rh-neg). Furthermore PCR amplification could also be carried out on DNA samples from persons with weak (Dweak) or partial (Dcat) RhD antigens.

CONCLUSION

This method will be valuable in prenatal RhD typing after amniocentesis or after the isolation of fetal cells from maternal peripheral blood.

Influence of piroxicam coadministration on pharmacodynamic parameters and the plasma concentration/effect relationship of recombinant hirudin (CGP 39393)

Recombinant hirudins are currently under investigation for use in myocardial infarction and unstable angina. In this study the influence of piroxicam on the pharmacodynamics and pharmacokinetics of a recombinant hirudin preparation (CGP 39393) administered intravenously was determined. Twelve healthy, male volunteers received piroxicam 10 mg and matching placebo once daily for 12 days according to a double-blind, randomised cross-over design. On the 12th day, the dose of piroxicam was followed by a 6-hour infusion of hirudin 0.1 mg.kg-1.h-1. Plasma concentrations and urinary excretion of hirudin and repeated measurements of the activated partial thromboplastin time (APTT), bleeding time and platelet adhesion index were assessed up to 24 h after the start of the infusion. The maximum APTT was 83 s (placebo) and 84 s (piroxicam), 3 to 4 h after the start of the infusion, and was comparable on both study days. The AUD0-24 (APTT) came to 913 s.h.kg-1 under placebo and it was slightly increased to 1,017 s.h.kg-1 after piroxicam; the 95%- confidence interval according to MOSES ranged from 0.97 to 1.24, and the point estimator was 1.10. Bleeding time was significantly prolonged from 290 s under placebo to 345 s under piroxicam before the start of the infusion of hirudin. No further prolongation was found during or after the infusion. No change was observed in the platelet adhesion index. Responsiveness parameters according to a sigmoidal Emax-model were obtained from the hirudin-plasma concentration/effect (i.e. APTT-prolongation)-curves after placebo and piroxicam.(ABSTRACT TRUNCATED AT 250 WORDS)

Regression of deep vein thrombosis by i.v.-administration of a low molecular weight heparin--results of a pilot study

Twenty-five patients with phlebographically confirmed deep vein thrombosis of the lower limb were treated with intravenous infusions of low molecular weight heparin for 7 to 29 days. The mean dosage was 15.2 +/- 3.0 Uanti-Xa (equivalent 7.6 +/- 1.5 U-aPTT). Phlebograms were taken before, during and after the treatment with low molecular weight heparin and evaluated using the score system of Marder. Nearly complete recanalization of the occluded veins was found in six (24%) patients, improvement of the Marder score of 60 to 90% was found in four patients and of 30 to 60% in seven patients, while eight patients remained unchanged. With an average dose of 15.2 I.U./kg/h the heptest was prolonged to 70 to 120 seconds while the aPTT-level did not significantly increase. tPA-antigen-levels increased significantly in most of the patients after the third day of treatment, while PAI-activity remained unchanged. A positive conclusion between the decrease of the Marder score and the duration of treatment was found. Thus the low molecular weight heparin used in this investigation proved to be effective and safe in treating deep vein thrombosis.

Functional studies on platelets of a patient with an acquired disorder of platelet function associated with autoantibodies against membrane glycoprotein IIB/IIIA complex

Platelet functions have been studied of a 63 year old woman with a severe acquired thrombopathy. The platelets did not adhere to siliconized glass. Aggregation could not be induced by either ADP (1 microM) nor collagen (2 micrograms/ml), no release of serotonin was found under these conditions. Thrombin caused only a weak aggregation response. Quantitative analysis of platelet actin revealed a very low total actin content (473 micrograms/10(9) platelets) and an extremely low F-actin value (3% of total actin). Stimulation of platelets with 0.1 U/ml thrombin for 3 min resulted in an increase of only 5% F-actin, whereas ADP and collagen did not induce any actin polymerization. Ca2+ movement in the patient's platelets is severely impaired after ADP and collagen stimulation, whereas a normal Ca2+ movement was obtained by 0.1 U/ml thrombin. The inhibition of the functions of normal platelets (aggregation and actin polymerization) by addition of patient's serum (5-10% final concentration) points to receptor blockade by platelet autoantibodies in the patient's serum. The antibody was purified by adsorption on Protein-A-Sepharose. Addition of IgG-suspension (5% final concentration) to washed control platelets resulted in similar effects on aggregation and actin polymerization compared to the effects of patient's serum.

Acquired disorder of platelet function associated with autoantibodies against membrane glycoprotein IIb-IIIa complex--1. Glycoprotein analysis

A patient with idiopathic thrombocytopenic purpura developed after splenectomy a thrombasthenia-like severe haemorrhagic diathesis characterized by a normal or subnormal platelet count, prolonged bleeding time, strongly reduced platelet adhesion to glass and defective platelet aggregation in response to ADP and collagen. In contrast to hereditary thrombasthenia membrane glycoproteins (GP) IIb and IIIa were normally present in the patient's platelets. Immunoelectrophoretic analysis revealed an abnormal behaviour of the patient's GP IIb-IIIa complex. Autoantibodies against GP IIb-IIIa were detected in Triton-extracted washed platelets. Incubation of normal platelets with plasma from the patient resulted in a similar immunoelectrophoretic abnormality of the GP IIb-IIIa complex indicating that bound autoantibodies (IgG) are responsible for the abnormal immunoelectrophoretic behaviour of the patient's GP IIb-IIIa complex. Platelet fibrinogen was severely reduced similar to classical thrombasthenia suggesting that the GP IIb-IIIa complex is involved in platelet fibrinogen storage.

Effect of recombinant hirudin on cytosolic Ca2+ concentrations using different platelet stimulators

Cytosolic Ca2+ concentration, [Ca2+]i, and aggregation behavior of hirudinized platelet suspensions were examined under stimulation with thrombin, adenosine diphosphate, platelet-activating factor, collagen and the calcium ionophore, ionomycin. A rise in [Ca2+]i, a key step in platelet activation, was only inhibited by recombinant hirudin r-hirudin using the agonist thrombin. All other stimulators including ionomycin were not affected by r-hirudin. If hirudinized blood was gel-filtered before platelet stimulation, thrombin induced the same response as citrated platelet suspensions. Aggregation studies and calcium influx using various stimulators showed good correlation: only thrombin-induced aggregation was completely inhibited by r-hirudin. These results support the hypothesis that hirudin inhibits platelet function by thrombin binding and not by direct interaction with platelets.

Platelet membrane defects in fawn hooded bleeder rats

An inbred strain of fawn hooded rats with a congenital platelet defect shows a marked bleeding tendency with prolonged bleeding time. This haemorrhagic disorder has been exclusively related to a deficiency of nucleotides in platelet dense granules. When tested in cell electrophoresis platelets from fawn hooded bleeder rats showed a significantly lower electrophoretic mobility than normal rat platelets. Subsequent studies on the platelet membrane protein pattern by high resolution two-dimensional gel electrophoresis revealed the deficiency of a membrane glycoprotein (apparent molecular mass 90.000, isoelectric point 5.6), which is detectable in normal rat platelets after surface labeling by periodate-tritiated sodium borohydride. It seems likely, that this glycoprotein defect contributes at least partially to the disorder of platelet function in fawn hooded bleeder rats.

Changes of spontaneous and induced platelet aggregation in the presence of a human endothelial cell monolayer

A new, simple method has been developed for the investigation of platelet aggregation in the presence of a cultured confluent human endothelial cell monolayer, in disk shaped rotating cuvettes, without magnetic stirring. The endothelial cells inhibited the aggregating effect of several inducers in a concentration dependent manner. At a platelet count of 5 x 10(5)/microliter in PRP e.g. the aggregating effect of 1 microgram/microliter thrombin was completely abolished. Spontaneous aggregation was also prevented by the EC-monolayer. A correlation could be established between the inhibitory effect of ECs and the number of platelets. In PRP with a platelet count of 7 x 10(-5)/microliters the inhibitory effect of the endothelial cell monolayer significantly decreased.

Haemostasiological parameters as risk factor for new arterial occlusions in diabetics

PARD is a prospective study sponsored by the German Research Council with the aim to establish if spontaneously enhanced platelet aggregation or changes of other hemostatic variables are risk factors for new vascular occlusions in diabetic patients. 363 diabetics (aged 45-65, 232 men, 131 women) have been observed for at least 5 years. Of the 232 men, 53 were on diet, 104 on oral antidiabetic agents and 75 on insulin. Of 131 women 16 were on diet, 46 on oral antidiabetic drugs and 69 on insulin. At entry a medical history was obtained and clinical examinations and laboratory tests were performed. Hemostatic tests and clinical examinations were repeated at 3 month's intervals. The life status was followed for all patients with the exception of 2. Until December 31, 1984, 42 patients had died, 23 from cardiovascular disease and 19 from other causes. 13 patients suffered a myocardial infarction, 11 a stroke and 53 a peripheral arterial occlusion. The occurrence of new vascular occlusions was significantly higher in men with enhanced spontaneous platelet aggregation measured by PAT III. This was not the case for women. Other hemostatic parameters with some relation to cardiovascular complications, again only in men, were fibrinogen, von Willebrand factor together with some established risk factors as triglycerides and hypertension.

Spontaneous platelet aggregation and coagulation parameters as risk factors for arterial occlusions in diabetics. Results of the PARD-study

PARD is a prospective study sponsored by the German Research Council with the aim to establish whether spontaneously enhanced platelet aggregation or changes of other hemostatic parameters are risk factors for new vascular occlusions in diabetic patients. 363 diabetic patients (aged 45-65, 232 men, 131 women) were observed for 5 years. Of the 232 men, 53 were on diet, 104 on oral antidiabetic drugs and 75 on insulin. Of 131 women 16 were on diet, 46 on oral antidiabetic drugs and 69 on insulin. At entry clinical examination and laboratory tests were performed, covering the known risk factors for cardiovascular complications. Hemostatic tests and clinical examination were performed at 3 months' intervals. The life status was followed for all patients. Endpoints were carefully defined. Until December 31, 1984, 42 patients died, 23 from cardiovascular disease and 19 from other causes. 13 patients suffered a myocardial infarction, 10 a stroke and 53 peripheral arterial occlusions. The occurrence of new vascular occlusions was significantly higher in those men with enhanced spontaneous platelet aggregation measured by PAT III angle alpha above 40 degrees at entry as compared to those with lower values. This was not the case for women. Other hemostatic parameters, which had also some relation to cardiovascular complications, in men were fibrinogen and F. VIII R:Ag. Established risk factors for which a significant relation to cardiovascular complications was observed in this study, were smoking, duration of diabetes, diastolic blood pressure, cholesterol, triglycerides and also HbA1. The results of the PARD-study have verified the hypothesis that spontaneous aggregation is a major risk factor for future vascular occlusions in diabetic men. They also lead to the hypothesis that high levels of F. VIII R:Ag and fibrinogen are further indicators of progressive vascular disease and may be useful as predictors of new vascular occlusions in combination with such established risk factors as smoking, duration of diabetes, diastolic blood pressure, cholesterol, and triglycerides.

Substitution of antithrombin III

AT III substitution is indicated in patients with inherited antithrombin III deficiency if these patients suffer acute thrombosis, if they have to be treated surgically and in the case of pregnancy in women with AT III deficiency who have an abortion or thrombosis, as well as during and after delivery. In acquired antithrombin III deficiency such as in patients with liver cirrhosis or the nephrotic syndrome, AT III substitution may be necessary if thrombotic complications occur. AT III substitution has been propagated especially in patients with polytrauma, septicaemia, DIC, acute liver failure and in toxaemia. In AT III substitution initial doses of 1 U/kg body weight are used to reach a 1,5% rise in plasma AT III level. If AT III turnover is normal a rise above 80% of normal should be achieved. If AT III turnover is increased, much higher initial and maintenance doses may be needed to normalize plasma AT III levels and to block DIC.

Biochemical and morphological investigations of the toxicity of a Capmul preparation and a bile salt-EDTA solution in patients with bile duct stones

Seventeen patients with bile duct calculi were treated alternately with a preparation of glycerol octanoate and a bile salt-EDTA solution via a nasobiliary tube. Of 14 patients (group I), it was necessary to operate on four immediately after irrigation therapy, success resulted from this conservative therapy in eight (57%) cases and two were unchanged. Laboratory investigations showed a decrease in zinc and copper concentrations in the serum. Of the patients 50-60% suffered from vomiting and diarrhea. For three patients (group II), there was an interval of 6-26 days between the end of the therapy and operation. Histological findings in the patients in group I and II subjected to operation included acute ulcerative and chronic inflammation in gallbladder and common bile duct walls. Since the alterations were of minor degree in four of the seven patients who subsequently underwent surgery the risk of irrigation therapy seems to be acceptable.

[Nonocclusive mesenteric ischemia (author's transl)]

This report intends to emphasize the importance of selective angiography in nonocclusive mesenteric ischemia (NMI). In a 67-year-old male with abdominal pain and weight loss the diagnosis of NMI was made angiographically after enteroclysis had shown extensive ulcerative jejunitis. In this condition, where constriction and obliteration of vasa recta of the superior mesenteric artery are present, operation is contraindicated. Current status of still incomplete understanding of the disease is discussed.