Biomedical subjects

B Kehrel

Publications and source records attributed to B Kehrel.

At least 19 recordsLinked to original sources

PubMed1997

Low-density lipoproteins inhibit the Na+/H+ antiport in human platelets. A novel mechanism enhancing platelet activity in hypercholesterolemia.

BACKGROUND: LDL have been reported to augment platelet activation, and increased platelet reactivity has been observed in familial hypercholesterolemia. However, the underlying mechanisms of this putatively atherogenic effect is unknown. Because intracellular pH (pHi) may play an important role in platelet function, we examined the influence of LDL on pHi and Na+/H+ antiport activity in human platelets and compared it with the effect of [3-methylsulfonyl-4-piperidinobenzoyl] guanidine hydrochloride (HOE 694), a selective Na+/H+ antiport inhibitor. METHODS AND RESULTS: Using a fluorescent dye technique, we demonstrated that incubation of platelets with physiological concentrations of LDL or with HOE 694 decreased pHi. In addition, both LDL and HOE 694 inhibited the Na+/H+ antiport in platelets treated with sodium propionate or thrombin. The inhibitory effect of LDL was observed both in normal and in glycoprotein (GP)IIb/IIIa-as well as in GPIIIb (CD36)-deficient platelets and was not influenced by the covalent modification of apolipoprotein B lysine residues, suggesting that specific LDL binding sites were not involved. Thrombin-induced phosphoinositide breakdown, diacylglycerol formation, and Ca2+ mobilization, as well as platelet aggregation and granule secretion, were potentiated by both LDL and HOE 694. pHi and Na+/H+ antiport activity were significantly reduced in platelets from patients with familial hypercholesterolemia. Both parameters were normalized after normalization of LDL levels by apheresis treatment. CONCLUSIONS: LDL inhibits the Na+/H+ antiport most likely via receptor-independent mechanisms, thereby augmenting platelet reactivity. This novel mechanisms explains increased platelet reactivity in patients with familial hypercholesterolemia and may contribute to the atherogenic potential of LDL.

Adult↗

PubMed1996

Flush heparin during cardiac catheterisation prevents long-term coagulation activation in children without APC-resistance-preliminary results.

This study was designed to prospectively evaluate haemostatic activation in 75 children undergoing cardiac catheterisation with intermittent flush heparin (10 IU/ml saline) and to relate these data to clinical findings and inherited risk factors for thrombophilia. In addition to flush heparin in infants < 6 months of age in whom additional arterial catheterisation was performed (n = 5) or patients with thrombophilia, heparin (300-400 IU/kg/d) was administered for a further 24 h. APTT was prolonged and anti Xa activity was significantly increased at the end of catheterisation and returned to normal 24 hours later. Whereas thrombin generation (F1 + 2) showed a significant coagulation activation at the end of catheterisation, no concomitant fibrinolytic activation (D-Dimer) was observed. Four children showed resistance to APC: one of them in whom stroke had occurred before and one additional child heterozygous for APCR received further prophylactic heparin. Two neonates with APCR and flush heparin only suffered from thrombosis after catheterisation. No further thrombotic events occurred. This study indicates that low-dose flush heparin during catheterisation may prevent long-term haemostatic activation in children without thrombophilia. Whether further heparin after cardiac catheterisation in children with APCR prevents vascular insults requires a more intensive study.

Adolescent↗

PubMed1996

Thrombospondin measured in whole blood--an indicator of platelet activation.

Abnormal platelet activation may be involved in prethrombotic states and lead to thromboembolism. When platelets become activated, they release thrombospondin (TSP) from their alpha-granules which binds mainly to the surface of activated platelets, platelet-derived microparticles and other blood cells. To determine bound as well as free TSP in a single assay, we developed an indirect ELISA to measure TSP in fixed whole blood. The intra-assay variance was less than 5% and 97% of purified standard TSP, added to whole blood samples, was recovered with the ELISA. Blood collected with a 20G needle into a syringe resulted in lower "whole blood TSP' values than blood collected with the Vacutainer system. Whole blood TSP levels were measured in 66 healthy blood donors (20F, 46M) aged 25-75 years. The mean whole blood TSP concentration was 33 +/- 19 ng/ml. No significant difference in whole blood TSP was found between healthy females and males (35 +/- 23 ng/ml vs. 33 +/- 17 ng/ml).

Adult↗

PubMed1996

High density lipoproteins enhance the Na+/H+ antiport in human platelets.

In the present study, we investigated the effect of high density lipoproteins 3 (HDL3) on Na+/H+ exchanger activity and cytosolic pH (pHi) in human platelets. HDL3 alone failed to affect pHi, but preincubation with HDL3 significantly enhanced the Na+/H+ antiport activation brought about by acidification with 100 mM sodium propionate or stimulation with 0.05 U/ml thrombin. the stimulatory effect of HDL3 was unaffected by indomethacin excluding a role for cyclooxygenase products. The HDL3 effect was not mediated by Ca2+/calmodulin-dependent protein kinase as HDL3 failed to increase cytosolic free calcium concentration. However, the potentiating effect of HDL3 was completely blocked in the presence of the protein kinase C inhibitor, bisindoylmaleimide and the phosphatidylcholine-specific phospholipase C inhibitor, D609. Furthermore, the effect of HDL3 was abolished after covalent modification of HDL3 with dimethylsuberimidate and was not observed in platelets from Glanzmann thrombasthenia type 1 which do not express GP IIb/IIIa, as well as in platelets preincubated with anti-GP IIb/IIIa polyclonal antibodies. We conclude that HDL3 enhances the sodium propionate- and thrombin-induced Na+/H+ antiport activity in human platelets via binding to GP IIb/IIIa and activation of protein kinase C and phosphatidylcholine-specific phospholipase C.

Blood Platelets↗

PubMed1995

HDL3 activates phospholipase D in normal but not in glycoprotein IIb/IIIa-deficient platelets.

Glycoprotein IIb/IIIa has been proposed as the platelet receptor for high density lipoproteins (HDL3). We characterized the HDL3-induced second messenger response in normal and glycoprotein IIb/IIIa-deficient platelets. In normal platelets physiological concentrations of HDL3 induced the time-dependent generation of phosphatidic acid in the absence of phosphoinositide turnover. The rise in phosphatidic acid preceded that of diacyglycerol which was inconsistent with phospholipase C/diacylglycerol kinase pathway being the source of phosphatidic acid and suggested the involvement of phospholipase D. In the presence of butanol, HDL3 stimulated the accumulation of phosphatidylbutanol, an unequivocal indicator of phospholipase D activity. No increase in phosphatidic acid, diacylglycerol, and phosphatidylbutanol was observed upon addition of HDL3 to glycoprotein IIb/IIIa-deficient platelets. We conclude that phosphatidic acid is generated in HDL3-stimulated platelets by phospholipase D and that glycoprotein IIb/IIIa is the receptor involved in this process.

Diglycerides↗

PubMed1995

Acquired von Willebrand disease in malignant peripheral neuroectodermal tumor (PNET).

In week 12 of the EICESS 92 protocol a 12-year-old boy with pelvic PNET developed acquired von Willebrand disease: bleeding time was prolonged (> 15 min) and von Willebrand factor antigen (54%) and ristocetin cofactor activity (50) were reduced. Platelet aggregations with thrombin and collagen and the number of major platelet glycoproteins/per platelet did not differ from the controls. After Haemate P (Behring Werke, Marburg, Germany) bleeding time normalized and surgery could be performed without occurrence of bleeding episodes. Three weeks after surgery bleeding time, ristocetin cofactor activity, and von Willebrand factor antigen increased to normal paediatric values. Without occurrence of further bleeding episodes the patient received another 10 courses of polychemotherapy (EICESS 92).

Bone Neoplasms↗

PubMed1995

Platelet-collagen interactions.

The collagens belong to the constituents of the subendothelium that determine the thrombogenicity of the vessel wall. The existence of several genetically distinct collagens is well documented. To date, 19 collagens have been characterized. The collagens are divided into the fibril forming collagens and the non-fibril forming collagens. At least nine of the different collagens--type I, III, IV, V, VI, VIII, XII, XIII, XIV--were found in the vessel wall. All collagen molecules are built of three chains in a triple-helical conformation. Some collagens also contain large parts of non-collagenous domains. An interesting example for complex collagens is collagen type VI for it shares non-collagenous domains with the von Willebrand factor A domain, the platelet glycoprotein Ib, fibronectin type III repeats, and Kunitz type protease inhibitor. Monomeric and fibrillar collagens effectively support platelet adhesion, whereas for collagen-induced platelet aggregation and secretion, the native, triple-helical structure of collagen is required. The platelet reactive sites in collagens type I and III have been studied intensively. Using CNBr-peptides three aggregatory sites in the alpha 1(I) chain and one in the alpha 1(III) chain have been found. Cyanogen bromide fragments of collagen type I were also used to measure platelet adhesion under flow conditions. alpha 1(I)CB3 strongly supports platelet adhesion. The two peptides alpha 1(I)CB3 and alpha 1(III)CB4 are highly homologous. alpha 1(III)CB4 is highly aggregatory. Several substances are known to interfere at different levels with the platelet-collagen interactions and have been identified in blood-feeding animals. Among them are the "leech anti-platelet protein" (LAPP), calin, moubatin, and pallidipin.

Animals↗

PubMed1994

Platelet adhesion to collagen and endothelial cell matrix under flow conditions is not dependent on platelet glycoprotein IV.

Platelet membrane glycoprotein IV (GPIV) is a cell-surface glycoprotein that has been proposed as a receptor for collagen. Recently, it has been shown that platelets with the Naka-negative phenotype lack GPIV on their surface, whereas donors with this phenotype are healthy and do not suffer from hematologic disorders. In this study, we compared Naka-negative platelets with normal platelets in adhesion to collagen types I, III, IV, and V and the extracellular matrix of endothelial cells (ECM) under static and flow conditions. No differences in platelet adhesion and subsequent aggregate formation on the collagens types I, III, and IV were observed under static and flow conditions. Adhesion of both homozygous and heterozygous Naka-negative platelets to collagen type V was strongly reduced under static conditions. Collagen type V was not adhesive under flow conditions. No difference in platelet adhesion to ECM was observed, which suggests that GPIV is not important in adhesion to subendothelium, for which ECM may serve as a model. These results indicate that GPIV is not a functional receptor for collagen under flow conditions.

Collagen↗

PubMed1993

Platelets deficient in glycoprotein IIIb aggregate normally to collagens type I and III but not to collagen type V.

The aggregation of platelets induced by collagens is considered an important step in primary hemostasis. Glycoprotein (GP) IIIb (GPIIIb, GPIV, CD36) has been proposed as a blood platelet receptor for collagen. Platelets from three healthy blood donors were shown to be clearly deficient in GPIIIb. These platelets aggregated normally in response to type I and III collagens. In addition, platelet factor 4, beta-thromboglobulin, and adenosine triphosphate (ATP) secretion in response to type I and III collagens was normal. The findings indicate that GPIIIb is not the major, essential collagen receptor for type I and III collagens. This would explain why all individuals with GPIIIb-deficient platelets examined so far are healthy and, in particular, show no apparent evidence of hemostatic problems. However, in contrast to control platelets, no aggregation and impaired platelet factor 4, beta-thromboglobulin, and ATP secretion was observed in response to type V collagen. Therefore, it is postulated that for type V collagen-induced aggregation both GPIa/IIa and GPIIIb are essential.

Adult↗

PubMed1993

Role of platelet membrane glycoproteins Ib/IX and IIb/IIIa, and of platelet alpha-granule proteins in platelet aggregation induced by human osteosarcoma cells.

We have previously shown that the platelet-aggregating activity of human MG-63 and HOS osteosarcoma cells depends at least in part upon tumor cell surface-associated thrombospondin, and suggested that platelet-osteosarcoma cell interactions could occur through interactions with specific platelet membrane receptors. In this study, the platelet-aggregating activity of MG-63 and HOS cells was studied by using a variety of platelet disorders. Both osteosarcoma cell lines induced a biphasic platelet aggregation response when added to normal platelet-rich plasma, while the second phase of aggregation was absent when added to gray platelets (deficiency in alpha-granule proteins) and to aspirin-treated platelets. Platelets from two unrelated patients with type I Glanzmann's thrombasthenia (deficiency in glycoprotein (GP) GPIIb/IIIa) did not aggregate at all with osteosarcoma cells. Using giant platelets from three patients with Bernard-Soulier syndrome (deficiency in GPIb/IX), the aggregation response induced by MG-63 and HOS cells was monophasic and reversible when compared to normal-sized platelets and to giant platelets from a patient with May-Hegglin anomaly (no membrane GP defect). Because GPIb serves as a receptor for von Willebrand factor during hemostasis, aggregation experiments were also conducted with the platelet-rich plasma of two patients with a low plasma von Willebrand factor concentration (type I von Willebrand's disease) before and after the infusion of deamino-D-arginine vasopressin. MG-63 and HOS cells induced biphasic platelet aggregation both before and after deamino-D-arginine vasopressin treatment, while the ristocetin-dependent binding of von Willebrand factor to platelets only occurred after deamino-D-arginine vasopressin treatment. Preincubation of normal platelet-rich plasma with monoclonal antibody SZ-2 directed against the von Willebrand binding domain of GPIb did not inhibit the platelet-aggregation activity of osteosarcoma cells, whereas anti-GPIb antibody SZ-2 did inhibit ristocetin-induced platelet agglutination. In addition, anti-GPIX antibodies did not affect platelet-osteosarcoma cell interactions. In conclusion, our data demonstrate that the first phase of the platelet-aggregating activity of human osteosarcoma cells is initiated by the interaction of these tumor cells with platelet membrane GPIIb/IIIa, whereas the second phase, even if plasma von Willebrand factor is deficient, involves platelet membrane GPIb and the participation of platelet alpha-granule proteins in membrane-mediated events, making aggregation irreversible.

Antibodies, Monoclonal↗

PubMed1993

The platelet glycoprotein IIb/IIIa complex is involved in the adhesion of activated platelets to leukocytes.

The adhesion of activated platelets to leukocytes (rosette formation) seems to be mediated by CD62 on platelets and its counter-receptor (CD15 or a sialic acid-containing glycoprotein) on polymorphonuclear leukocytes (PMNL). However, neither treatment of platelets with an anti-CD62 antibody or fucoidan nor treatment of PMNL with anti-CD15 antibody or neuraminidase are able to inhibit completely the adhesion. Therefore, we have studied the platelet GPIIb/IIIa complex (CD41a) for its involvement in the adhesion of activated platelets to PMNL. The following evidences point to a participation of CD41a in the adhesion of activated platelets to leukocytes: a) inhibition of adhesion by monoclonal antibodies (mab) raised toward CD41a, b) inhibition of adhesion by peptides such as RGDS and echistatin, c) inhibition of adhesion by dissociation of the CD41a complex with EGTA, and d) inhibition of rosette formation using platelets from a thrombasthenic patient which have almost no CD41a in the surface membrane but a normal expression of CD62. It is likely that fibrinogen is involved in the adhesion of platelets to PMNL via CD41a, since fibrinogen increases the rosette formation of ADP-stimulated platelets. Furthermore, the incubation of unstimulated platelets with fibrinogen and an antibody raised against glycoprotein IIIa which stimulates fibrinogen binding to the platelet surface results in an enlarged rosette formation.

Amino Acid Sequence↗

PubMed1993

Autoantibodies against the platelet glycoproteins (GP) IIb/IIIa, Ia/IIa, and IV and partial deficiency in GPIV in a patient with a bleeding disorder and a defective platelet collagen interaction.

To evaluate the physiologic importance of the different collagen receptors on platelets, we screened 806 patients admitted to the hospital because of hemorrhagic diathesis for eventual laboratory evidence of a pathologic platelet collagen interaction, and found 5 patients with an isolated deficiency in collagen-induced platelet aggregation. Four of these five patients had a partial defect, one had a complete defect. The structural and functional analysis of the platelets from the patient with a complete defect showed a deficiency in glycoprotein (GP) IV and autoantibodies against GPIIb/IIIa, GPIa/IIa, and GPIV. Patient plasma had only a minimal effect on normal control platelets and Naka-negative platelets. The analyses of the defect in the patient and of the data in the literature suggest that a single defect may not result in clinical bleeding (GPIV-deficient patients do not bleed), but may become symptomatic in combination with another defect such as the autoantibodies against GPIa/IIa, GPIV, and/or GPIIb/IIIa, all of which are involved in platelet collagen interactions (three of four of our immune thrombocytopenic purpura patients with anti-GPIV and anti-GPIIb/IIIa autoantibodies had a bleeding disorder). We hypothesize that it is the synergism of two abnormalities that results in the defective function, a mechanism that is in agreement with earlier studies on platelet collagen interaction that suggests that a double defect in platelet collagen interactions is required to become clinically apparent.

Adult↗

PubMed1993

Platelet membrane activation markers are predictive for increased risk of acute ischemic events after PTCA.

BACKGROUND: We wished to investigate whether platelet activation is related to the clinical outcome during the 24 hours immediately after elective percutaneous transluminal coronary angioplasty (PTCA). METHODS AND RESULTS: In 102 patients with high-grade coronary stenosis admitted for elective PTCA, preprocedural platelet activation was characterized by flow cytometric measurement of the proteins CD62, CD63, and thrombospondin expressed on the platelet surface membrane. The prevalence of acute ischemic events during the 24 hours immediately after the procedure was then related to the pre-PTCA platelet activation status. Fifty-six patients were classified as "nonactivated," whereas 46 patients showed an increased percentage of activated platelets. Two patients developed acute occlusion (1.96%) and four patients high-grade restenosis (3.92%), as confirmed by second-look coronary angiography. All events occurred in patients classified as "activated" (six of 46, or 13%). None of these patients received beta-blocker medication, which was associated with lower expression of platelet membrane activation markers. In the nonactivated patient group, no clinical events were found (0 of 56, or 0%). This difference in prevalence is significant (p = 0.007). CONCLUSIONS: We conclude that analysis of platelet membrane activation markers may help to predict an increased risk of acute ischemic events after angioplasty.

Angioplasty, Balloon, Coronary↗

PubMed1991

Thrombospondin binds normally to glycoprotein IIIb deficient platelets.

Glycoprotein IIIb (GPIV, CD36) has been proposed as the platelet receptor for thrombospondin (TSP). We found two healthy blood donors, whose platelets were shown to be GPIIIb deficient. These platelets expressed endogeneous TSP as control platelets and their binding capacity for exogeneous TSP was the same. These results indicate that GPIIIb is not the major TSP receptor on platelets. However, it is not yet possible to exclude that in GPIIIb-deficient platelets other proteins may substitute for GPIIIb in TSP binding.

Adult↗

PubMed1991

Large platelets circulate in an activated state in diabetes mellitus.

Diabetes mellitus is associated with aggravated development of vascular complications. Yet, it has not been established whether platelet hyperreactivity contributes as a pathogenetic factor. In order to study the role of activated platelets in diabetes mellitus, we investigated the expression of the membrane activation markers CD63 (GP53) and CD62 (GMP-140) as direct indicators of in vivo activation. The CD63-positive fraction was significantly higher in patients (6.1% X 3.7 +/- 1) than in controls (2.7% X 3 +/- 1). In parallel, the CD62-positive fraction was significantly elevated in patients to 5% X 2.5 +/- 1 in comparison to controls (3% X 2 +/- 1). Patients with angiopathy had a mean increase of 304% in CD63-positive and of 223% in CD62-positive platelets. Patients without clinically detectable angiopathy showed a trend to an increased fraction in CD63-/CD62-positive platelets. There was no correlation of the activation markers with fasting blood glucose, HbA1 or platelet count. CD63 platelet bound fluorescence significantly increased with platelet size in the patient group. We conclude that in diabetes mellitus an increased number of large platelets circulate in an activated state predominantly in patients with angiopathy. This could imply that platelets become activated by vascular lesions. The trend in patients without vascular disease, however, suggests that activated platelets may also basically contribute to the prethrombotic state in diabetes mellitus.

Adult↗

PubMed1991

Determination of platelet activation by assaying filamentous actin and detecting membrane alterations.

Thrombin stimulation of human gel-filtered platelets in an unstirred system (without aggregation) results in actin polymerisation. Concomitantly with actin polymerisation the activation markers (CD 63--glycoprotein 53, a 53 kD lysosomal protein and CD 62--GMP 140, a 140 kD alpha granule protein) increase on the platelet membrane as well as the specific binding of monoclonal antibodies to thrombospondin (P 10). Consequently, both assays run in parallel and indicate sensitively platelet activation. Our data also indicate that exposure of subcellular structures following granule fusion is a very early event when platelets are challenged by thrombin and involve a reorganisation of cytoskeletal structures. Cytochalasin E inhibits completely the thrombin-induced actin polymerisation and the platelet aggregation but only partially the thrombin-induced exposure of CD 63. The activation markers CD 62 and P 10 were not influenced.

Actins↗

PubMed1990

Identification of platelet antigens by immunoprecipitation of unlabelled platelet glycoproteins.

A time-saving and sensitive method for the identification of antigens on unlabelled platelet glycoproteins (GP) based on immunoprecipitation has been developed. Platelet solubilisates were incubated with antibodies to form GP-antibody complexes that were precipitated with Protein G Sepharose 4 Fast Flow (PGS). PGS-bound material was eluted, separated by SDS-PAGE under reducing conditions and visualized by silver staining. The method was designed as an alternative to radioimmunoprecipitation for laboratories not equipped to work with radioactive substances. It is proposed as a complementary procedure for the characterization of platelet GP antigens by murine monoclonal antibodies and human alloantibodies.

Acids↗

PubMed1990

Flow-cytometric detection of surface membrane alterations and concomitant changes in the cytoskeletal actin status of activated platelets.

Occlusive vascular diseases are promoted by a "prethrombotic state" with increased platelet activity. Polymerization of cytoskeletal proteins and exposure of subcellular structures or rebinding of secreted proteins have been characterized as early reactions after platelet activation preceding adhesion and aggregation. Here, we demonstrate the kinetic increase in specific binding of monoclonal antibodies to thrombospondin (P10) and to platelet membrane activation markers CD63 (GP53, a 53 kD lysosomal protein) and CD62 (GMP140, a 140 kD alpha granule protein) by using a flow-cytometric bio-assay and the related change in the actin status by using the DNase-I inhibition assay after stimulation of normal human platelets with 0.2 U/ml thrombin. F-actin was raised from 41% to 51% of total platelet actin content 30 s after stimulation and remained thereafter constant (50% at 60 s). Simultaneously, the percentage of P10, CD63, and CD62 positive platelets was elevated from 5.4%, 24.4%, and 9.1% to 67.4%, 80.2%, and 82.3% respectively. The mean number of P10, CD63, and CD62 antibody binding sites increased from 3,300, 1,715, and 2,146 to 6,400, 6,800, and 9,016 per platelet. Conclusively, changes in the organization of the cytoskeletal protein "actin" and exposure of subcellular structures indicating platelet secretion can be regarded as markers of early platelet activation. Thus, the parallel response in both analytical systems provides further support for the diagnostic concept of flow-cytometric detection of preactivated platelets in the peripheral blood by using fluochrome staining procedures detecting activation dependent structural alterations directly at the cellular level.

Actins↗