PAR-1 genotype influences platelet aggregation and procoagulant responses in patients with coronary artery disease prior to and during clopidogrel therapy

Genetic variations of the protease-activated receptor-1 (PAR-1) have been associated with platelet receptor density and linked to thrombin receptor-activating peptide (TRAP)-induced phenotypes of platelet aggregation and P-selectin expression. We investigated whether the PAR-1 intervening sequence-14 A>T dimorphism influences platelet procoagulant activity. We also determined whether the P2Y12 antagonist clopidogrel could offset any observed functional polymorphism of the PAR-1 receptor by inhibiting P2Y12-mediated amplification of TRAP-induced responses. We studied 54 patients listed for elective percutaneous coronary intervention assessing TRAP-induced platelet aggregation and markers of procoagulant activity. Platelet responses were measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. Each patient was genotyped for the PAR-1 intervening sequence-14 A/T dimorphism. Increased platelet aggregation and procoagulant responses were observed with PAR-1 A allele homozygotes. Clopidogrel significantly inhibited these platelet responses regardless of PAR-1 genotype, but did not offset the hyper-reactivity associated with the A/A homozygotes. We conclude that a common sequence variation within the PAR-1 gene influences TRAP-induced platelet procoagulant activity as well as aggregation. Higher platelet reactivity associated with PAR-1 IVSn-14 A allele homozygotes persists despite clopidogrel therapy. These individuals may be at higher risk of thromboembolic events and may require additional anti-platelet medication.

Endothelial progenitor cells: characterization, in vitro expansion, and prospects for autologous cell therapy

Injection of hematopoietic stem cells or endothelial progenitor cells (EPCs) expanded ex vivo has been shown to augment neovascularization in adult patients, but the precise origin and identity of the cell population responsible for these clinical benefits are controversial. The limited quantity of EPCs in the circulation has been the main obstacle to clinical trials. Several authors have therefore attempted to expand these cells ex vivo in order to obtain a homogeneous cell therapy product. One possible means of expanding EPCs ex vivo is to activate the thrombin receptor PAR-1 with the specific peptide SFLLRN. Indeed, PAR-1 activation promotes cell proliferation and C-X-C chemokine receptor type 4 (CXCR4) dependent migration and differentiation, with an overall angiogenic effect. This review summarizes the results and rationale of clinical trials of angiogenic therapy, the nature of EPCs, the different methods of ex vivo expansion, and current methods of quantification.

The angiopoietin pathway is modulated by PAR-1 activation on human endothelial progenitor cells

OBJECTIVES

The importance of protease-activated receptor-1 (PAR-1) in blood vessel development has been shown in knock-out mice. As endothelial progenitor cells (EPCs) express functional PAR-1, we examined whether PAR-1 stimulation by the peptide SFLLRN interfered with the angiopoietin pathway, that is EPC commitment, proliferation and migration.

METHODS AND RESULTS

Given the strong PAR-1 expression on CD34+ cells, we tested the effect of SFLLRN 75 micromol L(-1) on the emergence of EPCs from cord blood. PAR-1 activation did not modify the number of colonies or the day of emergence, in keeping with the lack of induction of angiopoietin 1 gene expression. Conversely, SFLLRN treatment of EPCs induced angiopoietin 2 gene expression and protein synthesis. Experiments with polyclonal blocking antibodies showed that angiopoietin 2 was involved in the proliferative effect of PAR-1 activation. PAR-1 activation also enhanced migration toward angiopoietin 1 in a Boyden chamber assay.

CONCLUSIONS

Our study demonstrates that PAR-1-induced proliferation of EPCs involves angiopoietin 2. PAR-1 also enhances EPC migration toward angiopoietin 1. These findings might explain the role of thrombin in neovascularization via the angiopoietin pathway.

[Acquired mutation of JAK2 tyrosine kinase and polycythaemia vera]

Polycythaemia vera is an acquired myeloproliferative disorder characterised by a polycythaemia resulting of a clonal disorder arising in a multipotent hematopoietic stem cell. The increase of red cell mass exposes to a high risk of arterial or venous thrombosis and thus requires a cytoreductive treatment. An acquired genetic mutation in exon 12 of the JAK2 tyrosine kinase gene, leading to a substitution of a valine to a phenylalanine (V617F), has been described in most polycythaemia vera patients. This mutation increases the phosphorylation activity of JAK2, promotes the spontaneous cellular growth and induces erythrocytosis in a mouse model. Prevalence studies of V617F JAK2 mutation in different myeloproliferative disorders have found this genetic alteration in half of idiopathic myelofibrosis and in one third of essential thrombocythaemia. This finding is a huge progress in the understanding of polycythaemia vera physiopathology, it will be also an useful tool for the diagnosis of myeloproliferative disorders and it opens a new field for the development of targeted therapeutic approaches in these disorders.

[Prognostic factors in chronic lymphocytic leukaemia: contribution of recent biological markers]

Chronic lymphocytic leukemia (CLL) is the most common lymphoid hemopathy in elderly. Diagnosis of CLL is easily made with a full blood count and immunophenotyping, but there is an heterogeneity in clinical evolution. Until now, scheduling of treatment is based on Rai or Binet staging systems. These staging systems can not distinguish patients with a rapid evolution and thus who will need an earlier treatment. In order to detect these patients, it is useful to have some relevant markers to predict disease evolution. This article reviews recent biologic markers that can be used to evaluate long term prognosis of CLL patients.

The specific thromboxane receptor antagonist S18886: pharmacokinetic and pharmacodynamic studies

OBJECTIVES AND PATIENTS

We conducted a multicenter double-blind pharmacokinetic/pharmacodynamic (PK/PD) study of the new oral thromboxane receptor antagonist S18886 in 30 patients with peripheral artery disease, who were randomized to receive five different oral dosages of S18886 (1, 2.5, 5, 10 or 30 mg) for 12 weeks (83 days). Primary objective was to determine the effect of S18886 on platelet aggregation ex vivo.

RESULTS

Pharmacokinetics of S18886 was linear, with peak plasma levels being reached between 30 min and 2 h and a terminal half-life of 5.8-10 h. No significant accumulation of S18886 in plasma was observed after repeated dosing. The relationship between the S18886 concentration and platelet inhibition was examined in terms of U46619-induced platelet aggregation. Over the range of doses studied, there was a predictable relation between the plasma drug concentration and the degree of platelet inhibition at each dose. Maximal inhibition of U46619-induced platelet aggregation was achieved within 1 h with all oral doses of S18886, and this effect was maintained for at least 12 h. The PK/PD relationship was direct, and U46619-induced platelet aggregation was strongly inhibited by S18886 plasma concentrations above 10 ng mL(-1). This concentration was thus the minimal effective antiplatelet level in this population, and was maintained only by the dosages of 10 and 30 mg. The safety profile of S18886 was excellent, whatever the unit dose, with no attributable adverse events.

CONCLUSION

The results of this study, which included modeling and simulation, help identify the minimal effective plasma concentration of S18886 required for potent antiplatelet efficacy in patients with stable peripheral arterial disease.

[Role of platelet dysfunction in the haemostatic manifestations occurring during essential thrombocythaemia]

Among myeloproliferative disorders, Essential Thrombocythaemia is the most frequent and the one associated with the better prognosis. Although median survival is above 15 years, Essential Thrombocythaemia may be complicated by haemostatic life-threatening manifestations. Occurrence of thromboembolic or haemorrhagic episodes, even both in a same patient, are not predictable and physiopathology of Essential Thrombocythaemia remains misunderstood. Many studies have been conducted to explain the mechanisms responsible for the haemostatic complications and to determine predictive biological factors in order to improve the management of patients. We report here a review of the potential roles of platelets in Essential Thrombocythaemia through their interaction with coagulation and fibrinolysis systems as well as with cellular components (leukocytes and endothelium). Many controversial data have been published so far. However, a deficiency in high molecular multimers of von Willebrand factor is currently admitted, as well as deficiency of platelet membrane proteins and the presence of circulating activated platelets, especially in erythromelalgia. However, no biological abnormality has been correlated with the clinical manifestations. The haemostatic complications are likely to result from a multifactorial process in which accumulated moderated risk factors unbalance the procoagulant/anticoagulant pathways.

[Myelodisplasic syndromes diagnosed in a geriatric hospital: morphological profile in 100 patients]

Myelodysplastic syndrome (MDS) is particularly common in geriatric practice. As few data are available in very elderly patients, we conducted a 54-month retrospective study in patients over 70 years with MDS diagnosed at Hôpital Charles Foix. Patients with cobalamine, folate or iron deficiency were excluded. Regarding biological and morphologic approaches, MDS patients were classified according to the FAB criteria. We then tempted to reclassify the patients according to the WHO criteria. The Bournemouth scoring system was used as a prognostic tool. During the study period, 100 patients were included, 29 males and 71 females, median age 86 +/- 7 years (70-103). At the time of bone marrow sampling, a peripheral blood cytopenia was documented in 64 patients, a bicytopenia in 27 patients and a pancytopenia in 9 patients. Isolated anaemia (Hb < 12 g/dL) was found in 60 patients and isolated thrombocytopenia (< 150 x 10(9)/L) in 4. Macrocytosis (MCV > 100 fL) was observed in 21 % of the cases. According to the FAB criteria, the 100 patients were classified as follows: refractory anaemia (RA): 79%; RA with ringed sideroblasts (RARS): 8%; RA with excess of blasts (RAEB): 8%; RAEB in transformation: 1%; chronic myelomonocytic leukaemia: 4%. According to the WHO classification, the patients were reclassified as follows: RA (unilineage) (with or without ringed sideroblasts): 10%; refractory cytopenia with multilineage dysplasia with or without ringed sideroblasts (RCMD): 73%; RAEB: 7% (RAEB-1 6%, RAEB-21%); MDS/Myeloproliferative disorder: 4%; unclassified (hypocellularity): 5%; acute leukaemia: 1%. In order to estimate prognosis at the time of the bone marrow aspirate, we calculated the Bournemouth'score: 8 patients scored 0,57 scored 1,25 scored 2,8 scored 3 and 2 scored 4. In this geriatric population, 83% cases of MDS are RA or RCMD (with or without sideroblasts); MDS with excess of blasts are uncommon. Thus, elderly patients under study with MDS were diagnosed at an earlier stage of the disease than younger ones from series published in the literature. Due to frequent comorbidities, geriatric patients may be symptomatic for a slight decrease of haemoglobin level. Therefore, elderly patients are investigated as soon as they present with moderate anaemia that may explain the early MDS diagnosis.

Implication of protein S thrombin-sensitive region with membrane binding via conformational changes in the gamma-carboxyglutamic acid-rich domain

In the vitamin K-dependent protein family, only protein S (PS) contains a thrombin-sensitive region (TSR), located between the domain containing the gamma-carboxyglutamic acid and the first epidermal growth factor-like domain. To better define the role of TSR in the PS molecule, we expressed a recombinant human PS (rHPS) and its analogue lacking TSR (rTSR-less), and prepared factor Xa- and thrombin-cleaved rHPS. A peptide reproducing TSR (TSR-peptide) was also synthesized in an attempt to obtain direct evidence of the domain involvement in PS anticoagulant activity. In a coagulation assay, both rTSR-less and factor Xa-cleaved PS were devoid of activated protein C cofactor activity. The TSR-peptide did not inhibit rHPS activity, showing that TSR must be embedded in the native protein to promote interaction with activated protein C. The binding of rHPS to activated platelets and to phospholipid vesicles was not modified after factor Xa- or thrombin-mediated TSR cleavage, whereas the binding of rTSR-less was markedly reduced. This suggested a role for TSR in conferring to PS a strong affinity for phospholipid membranes. TSR-peptide did not directly bind to activated platelets or compete with rHPS for phospholipid binding. The results of the present study show that TSR may not interact directly with membranes, but probably constrains the gamma-carboxyglutamic acid-rich domain in a conformation allowing optimal interaction with phospholipids.

Delivery management in a woman with thrombocytopenia of the May-Hegglin anomaly type

Thrombocytopenia of the May-Hegglin anomaly type was diagnosed in a woman with no past history of bleeding diathesis, who had been followed during her three pregnancies. No abnormal bleeding occurred although no platelet transfusion was administered during the second and third cesarean sections. Routine platelets transfusion is unnecessary but platelets should be available for use if abnormal bleeding occurs.

[Monitoring of tinzaparin in a ten day treatment dose in elderly patients]

PURPOSE

Renal impairment, which is frequently observed in elderly patients, raises the question of low molecular weight heparins treatment dose adjustment in this population. Thus, we conducted a prospective study to determine whether tinzaparin, administered subcutaneously at treatment dose (175 anti-Xa IU/kg) once daily for 10 days, does accumulate in patients older than 70 years of age.

METHODS

Accumulation criteria were an increase of plasma anti-Xa and anti-IIa levels determined prior to the first injection and on days 2, 5, 7 and 10. The characteristics of the 30 consecutive included patients receiving tinzaparin at treatment dose (six men, 24 women) were: age 87.0 +/- 5.9 years (range: 71-96 years), body weight: 62.7 +/- 14.6 kg (range: 38-90 kg) and creatinine clearance 40.6 +/- 15.3 mL/min (range: 20-72 mL/min).

RESULTS

None of the patients required a dose adjustment of tinzaparin over the 10-day treatment period. Anti-Xa and anti-IIa activity levels on day 2 were 0.66 +/- 0.20 IU/mL (range: 0.26-1.04 IU/mL) and 0.33 +/- 0.10 IU/mL (range: 0.18-0.55 IU/mL), respectively. These levels did not significantly change over the 10 days. These results favor the absence of the accumulation effect of tinzaparin. There was no correlation between anti-Xa and anti-IIa activities and age, weight, or creatinine clearance. Concerning the side-effects, only one minor hematoma at the injection site was reported.

CONCLUSION

Tinzaparin may thus be administered in older patients with renal impairment, at a treatment dose (175 anti-Xa IU/kg/d) for a 10-day treatment period, without accumulation effect nor hemorrhagic side-effect in patients with creatinine clearance greater than 20 mL/min.

Elderly patients treated with tinzaparin (Innohep) administered once daily (175 anti-Xa IU/kg): anti-Xa and anti-IIa activities over 10 days

Since low molecular weight heparins (LMWH) are partly eliminated by renal excretion, their pharmacodynamic profile may be modified in very elderly patients with age-related renal impairment. The aim of this prospective study was to determine whether tinzaparin (Innohep) 175 anti-Xa IU/kg administered subcutaneously once daily over 10 days does accumulate in hospital patients greater than 70 years of age. Plasma anti-Xa and anti-IIa amidolytic levels and APTT were determined prior to the first injection (day 0), and then, at peak level i.e. 5 h after the second injection (day 2) and subsequently on days 5, 7 and 10. Thirty consecutive inpatients (6 men, 24 women) requiring LMWHs at a curative dose for acute thromboembolic disease were included. Patients' characteristics (mean +/- SD) were: age 87.0+/-5.9 years (range 71-96), body weight 62.7+/-14.6 kg (range 38-90) and creatinine clearance 40.6+/-15.3 mL/min (range 20-72). The mean actual dose of tinzaparin delivered was 174.8 anti-Xa IU/kg. Since no patient had an anti-Xa activity above 1.5 IU/mL, the dose of tinzaparin remained fixed over 10 days. Anti-Xa and anti-IIa peak levels measured on day 2 were 0.66+/-0.20 IU/mL (range 0.26-1.04) and 0.33+/-0.10 IU/mL (range 0.18-0.55), respectively. Ex vivo anti-Xa/anti-IIa ratios were close to 2.1. APTT ratios (patient/control) were strongly correlated with anti-IIa activity (p <0.01). There was no progressive increase of the anti-Xa and anti-IIa activities after repeated administration of tinzaparin over the 10 day treatment period. No correlation was found between anti-Xa and anti-IIa activities and age, weight, or creatinine clearance. No major bleeding occurred during the study and only one minor haematoma at the injection site was reported. No thrombo-embolic complication or death occurred. Tinzaparin may thus be administered safely at a treatment dose (175 anti-Xa IU/kg) in older patients with age-related renal impairment. Neither dose adjustment, nor serial anti-Xa activity monitoring seems to be required in patients with creatinine clearance above 20 mL/min during the first ten day treatment.

Characterization of cleaved plasma protein S with a monoclonal antibody-based assay

A monoclonal antibody (mAb 5A5G2) recognized cleaved plasma protein S (PS) but not uncleaved PS. Interestingly, mAb 5A5G2 did not recognize thrombin-cleaved recombinant PS. Microsequencing of cleaved plasma PS showed a Q-S-T-N amino-terminal sequence, inferring cleavage after the Arg 60 residue. The mAb epitope was located within the sequence encompassing residues 61 to 73, i.e. the carboxy-terminal part of the thrombin-sensitive region (TSR). We used this mAb to develop an ELISA assay to quantify in vivo cleaved PS. In plasma from 10 normal subjects, about 10% of PS was cleaved (7.1% to 15.4%), with a more than 2-fold increase in the corresponding sera. We found increased levels of cleaved PS in 8 patients with disseminated intravascular coagulation (DIC) and decreased levels in 22 patients on long-term oral anticoagulant therapy, whereas cleaved PS levels were similar in 8 hemophiliacs and the 10 normal subjects. Cleaved PS levels did not correlate with prothrombin fragment 1+2 levels released after cleavage by FXa in any of the groups, suggesting that circulating FXa is not the main factor involved in the production of cleaved PS in vivo.

Expression and characterization of recombinant protein S with the Ser 460 Pro mutation

To characterize the putative biochemical modifications induced by the Ser 460 to Pro (Heerlen) mutation in protein S (PS), we expressed both wild-type (wt) and mutated recombinant PS in HEK cells. In SDS-polyacrylamide gels, r-PS Heerlen migrated at 71 kDa whereas r-wt PS migrated at 73 kDa, a difference abolished after deglycosylation by N-glycosidase, suggesting that the Ser 460 Pro mutation abolishes N-glycosylation of Asn 458. The affinity of r-wt PS and r-PS Heerlen for C4b-binding protein (C4b-BP) and for phospholipid vesicles was similar. Neither the enhancement of APC-dependent prolongation of the APTT, nor the specific enhancement of FVa and FVIIIa proteolysis by APC in purified systems was affected by the mutation. However, the Ser 460 Pro mutation induced a slight conformational change in the SHBG domain of the PS molecule, as shown by reduced binding affinity for monoclonal antibodies. The type III phenotype associated with the Heerlen mutation might thus result from a slightly modified rate of synthesis or catabolism. The resulting moderate decrease in the circulating PS concentration may modify the equilibrium between free PS and C4b-BP/PS complexes.

[Myelodysplastic syndromes]

Myelodysplastic syndromes (MDS) are clonal disorders of pluripotent hematopoietic stem cells. MDS occur predominantly over the age of 60 years. The diagnosis of MDS is based on the examination of both blood films and bone marrow aspirate. Diseases such as vitamin B12 and/or folate deficiency, or cytotoxic therapy leading to a marrow dysplasia should be ruled out. Five subtypes are described in the FAB classification : refractory anaemia or refractory cytopenia, refractory sideroblastic anaemia, refractory anaemia with excess of blasts, refractory anaemia with excess of blasts in transformation, chronic myelomonocytic leukaemia. This FAB classification is based on a small number of parameters: percentage of blood and marrow blasts, percentage of ringed sideroblasts and blood monocytes. The anaemia is typically normo- or macrocytic, non regenerative, and in half cases is associated with neutropenia and/or thrombocytopenia. During blood film examination, cell abnormalities have to be notified, i.e. anisocytosis, poikilocytosis of red cells, morphological abnormalities of neutrophils including hypogranulation, hypolobulation, abnormal large platelets. The prognostic and the treatment of MDS depend on the subtype of the FAB classification, the patient's age, the percentage of marrow blasts, the importance of cytopenia, the presence or not of cytogenetic abnormalities and the existence or not of HLA-identical donor.