Enhanced cell viscosity: A new phenotype associated with lamin A/C alterations

Lamin A/C is a well-established key contributor to nuclear stiffness and its role in nucleus mechanical properties has been extensively studied. However, its impact on whole-cell mechanics has been poorly addressed, particularly concerning measurable physical parameters. In this study, we combined microfluidic experiments with theoretical analyses to quantitatively estimate the whole-cell mechanical properties. This allowed us to characterize the mechanical changes induced in cells by lamin A/C alterations and prelamin A accumulation resulting from atazanavir treatment or lipodystrophy-associated LMNA R482W pathogenic variant. Our results reveal a distinctive increase in long-time viscosity as a signature of cells affected by lamin A/C alterations. Furthermore, they show that the whole-cell response to mechanical stress is driven not only by the nucleus but also by the nucleo-cytoskeleton links and the microtubule network. The enhanced cell viscosity assessed with our microfluidic assay could serve as a valuable diagnosis marker for lamin-related diseases.

Hemostatic abnormalities in patients with Ehlers-Danlos syndrome

Essentials Ehlers-Danlos Syndrome (EDS) is a rare heterogeneous group of inherited collagen disorders. A cohort of EDS patients was investigated for bleeding tendency and hemostatic abnormalities. EDS is associated with an increased risk of bleeding. EDS patients have platelet function abnormalities, whose severity correlates with bleeding risk. SUMMARY: Background Ehlers-Danlos syndrome (EDS) includes a heterogeneous group of connective tissue disorders affecting skin, bones, vessels, and other organs. Patients with EDS have an increased risk of bleeding, but a comprehensive study of hemostasis in EDS patients is lacking. Objective To investigate the bleeding tendency of a cohort of patients with EDS by using the Bleeding Assessment Tool of the ISTH, the bleeding severity score (BSS). Methods The BSS was defined as abnormal when it was ≥ 4 in men and ≥ 6 in women. Patients with a bleeding tendency were compared with those without in terms of type and number of hemostatic abnormalities. Results Fifty-nine of 141 patients with EDS (41.7%) had an abnormal BSS. Prothrombin time and activated partial thromboplastin time were slightly prolonged in 10 patients (7.1%) because of mild coagulation factor deficiencies, which were not responsible for the bleeding diathesis. von Willebrand factor antigen, ristocetin cofactor, endogenous thrombin potential and platelet count were normal in all patients. At least one platelet function abnormality was found in 53 patients (90%) with an abnormal BSS and in 64 (78%) with a normal BSS (adjusted odds ratio [OR] 2.55, 95% confidence interval [CI] 0.87-7.48). The risk of bleeding progressively increased with the number of platelet function abnormalities, reaching an OR of 5.19 (95% CI 1.32-20.45) when more than three abnormalities were detected. Conclusions Our results show that nearly half of patients with EDS have an abnormal BSS, which, in 90% of cases, appear, at least in part, to be attributable to platelet function abnormalities. Abnormalities of primary hemostasis may contribute to the risk of bleeding in patients with EDS.

Weighing polyelectrolytes packaged in viruslike particles

This Letter reports on the remarkable selectivity of capsid proteins for packaging synthetic polyelectrolytes in viruslike particles. By applying the contrast variation method in small-angle neutron scattering, we accurately estimated the mean mass of packaged polyelectrolytes ⟨Mp⟩ and that of the surrounding capsid ⟨Mcap⟩. Remarkably, the mass ratio ⟨Mp⟩/⟨Mcap⟩ was invariant for polyelectrolyte molecular weights spanning more than 2 orders of magnitude. To do so, capsids either packaged several chains simultaneously or selectively retained the shortest chains that could fit the capsid interior. Our data are in qualitative agreement with theoretical predictions based on free energy minimization and emphasize the importance of protein self-energy. These findings may give new insights into the nonspecific origin of genome selectivity for a number of viral systems.

Usefulness of PFA-100 testing in the diagnostic screening of patients with suspected abnormalities of hemostasis: comparison with the bleeding time

BACKGROUND

Global tests of hemostasis that are used to screen patients with clinical suspicion of bleeding disorders should help the physician to identify the phase of the hemostatic system that is abnormal and guide further diagnostic workup.

PATIENTS AND METHODS

We compared the performance of Platelet Function Analyzer-100 (PFA-100) closure time (CT) with bleeding time (BT), both of which are screening tests for primary hemostasis, in the diagnostic workup of 128 consecutive patients who were screened for bleeding disorders. The sensitivities of BT and PFA-100 CT for known defects of hemostasis were evaluated; in addition, we calculated their correlation with the levels of severity of the bleeding symptoms, which were recorded using a standardized questionnaire.

RESULTS

The sensitivity of PFA-100 testing was 71% for von Willebrand disease (VWD) [with both collagen-adenosine diphosphate (C-ADP) and collagen-epinephrine (C-EPI) cartridges]; 58% (C-EPI) and 8% (C-ADP) for platelet function disorders (PFDs); and the sensitivity of BT was 29% (VWD) and 33% (PFD). C-EPI CT was also prolonged in about 20% of patients with abnormalities of coagulation or fibrinolysis. Only the C-EPI CT was significantly associated with the levels of severity of the patients' bleeding scores.

CONCLUSIONS

BT and C-EPI are insufficiently sensitive to be recommended as hemostasis screening tests. The C-ADP cartridge, which is sensitive to VWD only, might prove useful in further diagnostic workup of defects of primary hemostasis. The association of C-EPI CT with the severity of bleeding symptoms as a useful predictor of risk of bleeding in clinical practise should be tested in properly designed studies.

Genetic characterization of patients with Bernard-Soulier syndrome and their relatives from Southern Iran

Bernard-Soulier syndrome (BSS) is a rare recessively inherited bleeding disorder caused by the deficiency of the platelet glycoprotein (Gp) complex Ib/IX/V that is the von Willebrand factor receptor on platelets. In patients suffering from BSS platelet adhesion is typically impaired, while platelet aggregation is normal; macrothrombocytopenia is a common feature. In this study three different families from Southern Iran were investigated. GpIb/IX/V platelet expression as detected by flow cytometry was less than 2% of normal in six cases and 12% in the remaining one. Platelet count was 35,000 platelets/microliter and iron deficiency anemia was common. All patients suffered from mucocutaneous bleeding at presentation and were born from consanguineous marriages. Genetic analysis demonstrated the presence of the same GpIX Phe55Ser missense mutation in two families and of a single base insertion (GP1BA C3221 ins), a never described mutation causing a frameshift in the GpIbalpha gene, in the third family. Among the family members studied several heterozygotes were identified. None of them, with one exception, had macrothrombocytopenia. In one family a slight reduction of GpIb/IX/V expression was observed.

Inhibition of the platelet P2Y12 receptor for adenosine diphosphate potentiates the antiplatelet effect of prostacyclin

BACKGROUND

Activation of two receptors for adenosine diphosphate (ADP), P2Y(1) and P2Y(12), is necessary for ADP-induced platelet aggregation (PA). It is generally believed that the antithrombotic effects of drugs inhibiting P2Y(12), such as clopidogrel, are uniquely mediated by inhibition of P2Y(12)-dependent PA. However, as P2Y(12) is negatively coupled to adenylyl cyclase (AC), its inhibition may also exert antithrombotic effects through the potentiation of prostacyclin (PGI(2)), which inhibit PA by stimulating AC.

OBJECTIVES

To test whether inhibition of P2Y(12) potentiates the antiplatelet effects of PGI(2).

METHODS

We measured the effects of PGI(2) (0.01-10 microm) on PA of washed human platelets induced by thrombin (0.5 U mL(-1)) in the presence or absence of ARC69931MX (anti-P2Y(12)) or MRS2500 (anti-P2Y(1)).

RESULTS

PGI(2) inhibited PA in the presence of anti-P2Y(12), but not in the presence of anti-P2Y(1) or in the absence of inhibitors. In contrast, dibutyryl-cyclicAMP inhibited PA both in the presence and absence of anti-P2Y(1) or anti-P2Y(12). PGI(2) increased platelet cyclicAMP levels only in the absence of thrombin or in the presence of thrombin plus anti-P2Y(12).

CONCLUSIONS

PGI(2) did not inhibit PA induced by thrombin, because its effect on AC was prevented by released ADP interacting with P2Y(12). Anti-P2Y(12) drugs, by rescuing AC activity, potentiate the antiplatelet effect of PGI(2), which may contribute to their antithrombotic effect.

New approaches for measuring coagulation

Although specific assays of coagulation factors are essential for diagnostic purposes they only give partial information about an individual's haemostatic state. This can be better assessed by various global tests, and recent developments and evaluations of five such tests are described in this symposium: the PFA-100; waveform analysis; thrombin generation; overall haemostasis potential; thrombelastography. Each test has advantages in various applications, but the thrombin generation test and waveform analysis have been found most useful in haemophilia, whilst the PFA-100 is helpful in von Willebrand's disease.

Low plasma levels of vitamin B(6) are independently associated with a heightened risk of deep-vein thrombosis

BACKGROUND

Elevated plasma levels of total homocysteine (tHcy) before and after an oral methionine load (PML) are associated with an elevated risk of deep-vein thrombosis (DVT). We investigated whether plasma levels of B vitamins that are involved in Hcy metabolism are associated with an elevated risk of DVT.

METHODS AND RESULTS

We compared 397 cases with previous DVT with 585 matched healthy controls. The plasma levels of folate, vitamin B(12), vitamin B(6,), and fasting and PML tHcy were measured. The ORs for DVT associated with high (>95th percentile) fasting levels and PML increases of tHcy were 2.1 (95% CI, 1.2 to 3.4) and 2.4 (95% CI, 1.5 to 3.9) after adjustment for established risk factors for DVT. Fasting plasma levels and PML increases in tHcy correlated negatively with vitamin levels. The crude OR for folate levels in the lowest quartile compared with the highest was 1.5 (95% CI, 1.1 to 2.1), and that for B(6) levels in the lowest and second quartiles compared with the highest was 1.5 (95% CI, 1.0 to 2.1). However, after adjustment for established risk factors and fasting and PML tHcy, the ORs for B(6) levels in the lowest and second quartiles only remained statistically significant (lowest quartile: OR, 1.8; 95% CI, 1.2 to 2.8; second quartile, OR, 1.9; 95% CI, 1.3 to 2.9).

CONCLUSIONS

High fasting and PML tHcy and low vitamin B(6) plasma levels are associated with an elevated risk for DVT independently of established risk factors for DVT. The association of low vitamin B(6) levels with the risk for DVT is independent of fasting and PML tHcy levels.

Multicenter study of homocysteine measurement--performance characteristics of different methods, influence of standards on interlaboratory agreement of results

After the demonstration that moderate hyperhomocysteinemia is associated with thrombosis, many hematological labs are becoming interested in total homocysteine (tHcy) measurement. This prompted us to organize a collaborative study to investigate the performance of methods used in this setting and to assess the between-lab comparability of results. Two pairs of pooled plasma (A1-A2 and B1-B2) were prepared at the coordinating Center. tHcy levels were normal in A1-A2 and moderately high in B1-B2. Within each pair tHcy levels were similar but not identical. Aliquots were taken from each pool to prepare sets of 100 samples (coded from 1 to 100). Each set consisted of 25 replicates for each pool. Samples were frozen and shipped in dry ice to 16 labs with a common frozen aqueous standard. Labs were asked to measure (in blind) tHcy with their methods and standards. Results were sent to the coordinating Center both as raw readings and as tHcy levels. The following methods were used: High Pressure Liquid Chromatography (HPLC) in 12 labs (home-made in 10 and commercial in 2); Enzyme Immuno Assays (EIA) in 2; Fluorescence Polarization Immunoassay (FPIA) in 2 and Capillary Electrophoresis (CE) in one. Results for paired pools (A1-A2 and B1-B2) were analyzed by the Student t test to assess for the ability to discriminate between similar but not identical tHcy levels. Results for each pool were used to assess within-lab reproducibility and between-lab comparability. Within-lab reproducibility expressed as median CV ranged from 12.6 to 13.9% (home-made HPLC); from 9.2 to 11.4% (commercial HPLC); from 21.8 to 24.2% (EIA); from 2.7 to 3.3% (FPIA) and from 11.2 to 22.0% (CE). All labs, except one using CE and 2 using home-made HPLC, were able to discriminate between similar tHcy levels in the normal range (pools A1-A2). Ten labs (4 using home-made HPLC, 2 commercial HPLC, 2 FPIA, one EIA and one CE) were able to discriminate between similar moderately high tHcy levels (pools B1-B2). Between-lab comparability expressed as CV was 14.0% 13.9%, 15.6% and 14.5% for pools A1, A2, B1, and B2. These values were considerably lower (CV values < 5.2%) when a common plasma standard was used for calculation of tHcy levels, while the use of a common aqueous standard failed to achieve the necessary harmonization. In conclusion, performance characteristics of the FPIA method compare favorably with the well-established HPLC methods. It is simpler and more suitable to be used by general hematological labs. Between-lab comparability of results is still a problem. The establishment of an international plasma standard would be of help to harmonize tHcy measurement across laboratories.

Platelets from a patient heterozygous for the defect of P2CYC receptors for ADP have a secretion defect despite normal thromboxane A2 production and normal granule stores: further evidence that some cases of platelet 'primary secretion defect' are heterozygous for a defect of P2CYC receptors

Two unrelated patients with a congenital bleeding diathesis associated with a severe defect of the platelet ADP receptor coupled to adenylate cyclase (P2(CYC)) have been described so far. In one of them, platelet secretion was shown to be abnormal. We recently showed that platelets with the primary secretion defect (PSD; characterized by abnormal secretion but normal granule stores, thromboxane A(2) production, and ADP-induced primary wave of aggregation) have a moderate defect of P2(CYC). Therefore, the interaction of ADP with the full complement of its receptors seems to be essential for normal platelet secretion, and PSD patients may be heterozygotes for the congenital severe defect of P2(CYC). In this study, we describe 2 new related patients with a severe defect of P2(CYC) and the son of one of them, who is to be considered an obligate heterozygote for the defect. The 2 patients with the severe defect had lifelong histories of abnormal bleeding, prolonged bleeding times, abnormalities of platelet aggregation and secretion, lack of inhibition of adenylate cyclase by ADP, and a deficiency of platelet-binding sites for [(33)P]2 MeS-ADP (240 and 225 sites per platelet; normal range, 530 to 1102). The son of one of them had a mildly prolonged bleeding time and abnormalities of platelet aggregation and secretion similar to those found in patients with PSD. In addition, his platelets showed a moderate defect of binding sites for [(33)P]2 MeS-ADP (430 sites per platelet) and of adenylate cyclase inhibition by ADP. This study of a family with the platelet disorder characterized by a defect of the platelet P2(CYC) receptor supports our hypothesis that the full complement of the platelet ADP receptors is essential for normal platelet secretion and that some patients with the common, ill-defined diagnosis of PSD are actually heterozygous for the defect.

A respiratory and allergy survey in textile workers employed in early stages of wool processing

OBJECTIVES

To determine frequency and type of respiratory and allergic symptoms in textile workers employed in early stages of wool processing.

METHODS

A cross-sectional study was carried out in four wool textile mills. 202 subjects (n. 148 males, 54 females, mean age 38.9 yrs, SD 9.5) employed in early stages (combing, n. 138, carding, n. 64) of wool processing were examined and an environmental survey was carried out to determine the level of wool dust exposure. All subjects were submitted to clinical interview, spirometry and measurement of serum specific IgE (s-IgE) against extracts of two wool lots (Australia and New Zealand) by means of RAST. In the subjects with a positive questionnaire for allergic symptoms serum specific IgE for common pneumoallergens were measured (PHADIATOP test).

RESULTS

We found higher air dust concentrations during carding operations (inspirable fraction-IF-: range 1.6-20 mg/m3; respirable fraction (RF): 0.5-6.9 mg/m3) and lower concentrations during combing (IF 0.3-0.7 mg/m3, RF 0.1-0.3 mg/m3). 70 out of 202 subjects (34.7%, n. 26 employed in carding and n. 44 in combing operations) reported work-related symptoms. Cutaneous itching was reported by 30 subjects, upper airway irritation by 24, ocular irritation by 17 and dyspnoea by 5. Globally 27 subjects (13.4%) had respiratory work-related symptoms. 12 subjects reported only seasonal respiratory symptoms not related to work. Within the group of 82 symptomatic subjects, 62 (75.6%) had serum specific IgE for common pneumoallergens. In the whole group (n. 202) mean basal FEV-1 was L 3.6, SD 0.9 (103.6% of predicted values). No significant difference was found in basal FEV-1 between carding and combing workers. No s-IgE against the two wool extracts was detectable in any of the 202 examined subjects.

CONCLUSIONS

Our data show that in early stages of wool processing: 1) the overall frequency of respiratory work-related symptoms is low and does not seem to be related to the stages of processing, 2) symptoms are mainly nasal and/or ocular; 3) serum s-IgE against wool extracts are not detectable. We conclude that respiratory allergy risk in wool textile mills is low.

Evaluation of platelet function with the PFA-100 system in patients with congenital defects of platelet secretion

The template bleeding time is still the screening test for defects of platelet function, although it is an invasive and poorly reproducible technique. The PFA-100 measures platelet function at high shear. Whole blood is aspirated through a capillary to an aperture of a membrane coated with platelet agonists. The system measures the time required to obtain occlusion of the aperture by a platelet plug (closure time). We measured the closure times in the PFA-100 system and the bleeding time in seven patients with delta-storage pool deficiency, 10 patients with "primary secretion defect" (not due to abnormalities of platelet granules or the arachidonate pathway), and 40 controls. Measurements were repeated I and 4 hours after intravenous infusion of desmopressin in six delta-storage pool deficiency and eight primary secretion defect patients. Baseline bleeding time and closure times with the collagen/epinephrine cartridge were longer in delta-storage pool deficiency and primary secretion defect patients than in controls. In contrast, closure times with the collagen/adenosine diphosphate cartridge were normal in both delta-storage pool deficiency and primary secretion defect patients. Treatment with desmopressin increased the plasma von Willebrand Factor levels, shortened the prolonged bleeding time, shortened the closure times with the collagen/adenosine diphosphate cartridge, and normalized the closure times with the collagen/ epinephrine cartridge. Therefore, the PFA-100 test may be a less invasive alternative to the bleeding time in the diagnosis and therapeutic monitoring of patients with platelet secretion defects. The collagen/epinephrine cartridge is more sensitive than the collagen/adenosine diphosphate cartridge to defects of platelet secretion.

Evaluation of the PFA-100 system in the diagnosis and therapeutic monitoring of patients with von Willebrand disease

We have evaluated platelet function at high shear with the PFA-100 system in different subtypes of von Willebrand disease (vWD), before and after the intravenous infusions of desmopressin or a factor-VIII/von Willebrand factor (vWF) concentrate. Closure times with the PFA-100 system were determined for both the collagen/ADP and the collagen/epinephrine cartridges in 52 patients with vWD (9 type 1 "platelet normal", 5 type 1 "platelet-discordant", 8 type 1 "platelet-low", 6 type 2A, 9 type 2B, 6 type 2M Vicenza. 6 type 3 and 3 acquired vWD) and 40 controls. Measurements were repeated 1 and 4 h after the i.v. infusion of desmopressin (0.3 microg/Kg) in 26 patients with types 1, type 2M Vicenza or type 2A vWD, or of a factorVIII/vWF concentrate (Alphanate HT, 60 U/Kg) in 4 patients with type 3 vWD. At all time points, vWF plasma levels and the bleeding time (Symplate II) were also determined. Baseline closure times were longer in vWD patients than in controls with both the collagen/ADP and the collagen/ epinephrine cartridges. The sensitivity of the PFA-100 system (88% and 87% with the two cartridges) was higher than that of the bleeding time (65%). Treatment with desmopressin normalized the closure times in patients with type 1 "platelet-normal" or type 2M Vicenza vWD, had no significant effects in patients with type 1 "platelet-low", type 1 "platelet-discordant" or type 2A vWD. Infusion of a factorVIII/vWF concentrate in patients with type 3 vWD slightly shortened their prolonged closure times. In general, changes in PFA-100 were paralleled by shortenings of the bleeding times and increases in plasma vWF levels. The PFA-100 test reflects vWF-dependent platelet function under high shear stress and could be useful in the diagnosis and therapeutic monitoring of patients with vWD.

The P2Y1 receptor is normal in a patient presenting a severe deficiency of ADP-induced platelet aggregation

ADP is a key stimulus inducing platelet shape change and aggregation, a rise in internal calcium and inhibition of adenylyl cyclase. These signaling pathways are thought to be activated by three independent receptors, but to date only the P2Y1 receptor responsible for calcium mobilization and the ionotropic P2X1 receptor have been identified. We report here the characteristics of the P2Y1 receptor in a patient presenting a selective deficiency of ADP-induced aggregation. Cloning of the P2Y1 gene revealed that the patient's DNA and mRNA were normal. Pharmacological studies showed that the P2Y1 receptor was expressed and functional in patient's platelets. Hence, the P2Y, receptor is not the cause of the impaired ADP-induced platelet aggregation in this patient. The P2X1 mRNA was also found to be present and normal. These findings add evidence to previous observations suggesting that a third P2 receptor coupled to adenylyl cyclase may be involved in ADP-induced platelet aggregation.

Plasma homocysteine levels in 10 patients with polycythemia

Polycythemia and hyperhomocysteinemia are risk factors for thrombosis. Since red blood cells actively metabolize methionine to homocysteine, we investigated whether or not patients with polycythemia have increased plasma levels of homocysteine, which might contribute to their increased thrombotic risk. In ten patients with polycythemia, the plasma homocysteine levels were measured before phlebotomy, three days after the procedure and 1-2 months later. The baseline mean plasma homocysteine levels in patients (9.7 +/- 1.6 mumol/L [+/-SD]) did not differ significantly from that found in 30 sex- and age-matched healthy controls (12.2 +/- 6.9). Despite a fall in the patients' mean [+/-SD] hematocrit from 0.50 +/- 0.02 at baseline to 0.47 +/- 0.03 three days after phlebotomy (significant at 95%) and to 0.48 +/- 0.02 after 1 to 2 months (not significant), the mean plasma homocysteine levels did not change significantly (9.9 +/- 2.3 mumol/L at 3 days and 9.7 +/- 2.1 mumol/L at 1-2 months). It is unlikely that high plasma homocysteine levels contribute to the increased thrombotic risk of polycythemic patients.

Partial inhibition of platelet aggregation by nebulized pentamidine in severe haemophiliacs

The antiparasite agent pentamidine has been shown to inhibit human platelet aggregation in vitro at concentrations that (potentially) may be attained in patient plasma after the administration of the drug by nebulizer. We measured platelet aggregation in platelet-rich plasma (PRP) before and after the administration of 300 mg nebulized pentamidine to 10 HIV-positive patients with severe haemophilia on prophylaxis against Pneumocystis carinii pneumonia. All patients had normal platelet counts. PAF-acether, U46619, collagen and ADP at different concentrations were used as agonists. Platelet aggregation was lower in PRP samples taken at the end of pentamidine administration and 1 h thereafter than in samples taken at the same time points in control experiments (without the administration of pentamidine). The inhibition of platelet aggregation was mild and tended to be overcome by higher concentrations of platelet agonists. The bleeding time was prolonged from 5 to 15 min in one patient but did not change in the remaining nine patients. In conclusion, this controlled study shows that nebulized pentamidine inhibits platelet aggregation in HIV-positive haemophiliacs without significantly affecting their bleeding times. Although this mild inhibitory effect may not be clinically relevant in haemophiliacs with normal platelet counts despite their defect in intrinsic coagulation, patients with HIV-related thrombocytopenia should be monitored to detect any excessive prolongation of their bleeding times after nebulized pentamidine.

Purinoceptors on blood platelets: further pharmacological and clinical evidence to suggest the presence of two ADP receptors

Platelet aggregation by ADP plays a major role in the development and extension of arterial thrombosis. The antithrombotic thienopyridine compounds ticlopidine and clopidogrel have proved useful tools to investigate the mechanisms of ADP-induced platelet activation. In essence, although clopidogrel has been shown to completely and selectively block ADP-induced platelet aggregation, G protein activation and inhibition of adenylyl cyclase, this drug does not affect shape change and Ca2+ influx. Binding studies, using the non-hydrolysable ligand [33P]2MeSADP, have shown that human platelets contain about 600 high-affinity binding sites for 2MeSADP (Kd approximately 5 nM). These sites present pharmacological characteristics of a P2T receptor. Clopidogrel treatment reduces the number of sites by 70% on rat platelets (from 1200 to 450) and leaves the residual binding sites resistant to clopidogrel. Moreover, patients with congenital impairment of ADP-induced platelet aggregation but normal shape change display very low levels of [33P]2MeSADP binding sites. The current data thus strongly suggest the presence of two ADP receptors, one responsible for shape change and rapid Ca2+ influx and the other a Gi protein-coupled receptor responsible for Ca2+ mobilization from internal stores, inhibition of adenylyl cyclase and platelet aggregation.

Platelet aggregation at high shear is impaired in patients with congenital defects of platelet secretion and is corrected by DDAVP: correlation with the bleeding time

Techniques measuring platelet aggregation in vitro under the high shear rate conditions that can be found in the microcirculation could reflect the status of primary hemostasis better than the turbidimetric technique. We studied platelet aggregation at high shear in patients with prolonged bleeding time caused by congenital platelet secretion defects such as delta-storage pool deficiency and primary secretion defect. Two different techniques were used: shear-induced platelet aggregation in a cone-and-plate viscometer and the filter aggregation test. With both techniques, platelet aggregation at high shear rate was defective in 14 patients with delta-storage pool deficiency and in 8 with primary secretion defect. There was a statistically significant correlation between platelet aggregation at high shear rate and the bleeding time. In patients with delta-storage pool deficiency, platelet aggregation at high shear rate and the bleeding time were significantly correlated with the platelet serotonin content. The intravenous infusion of 1-deamino-8-D-arginine vasopressin (DDAVP) (0.3 micrograms/kg) increased the plasma concentration of von Willebrand factor (vWf), shortened the bleeding time, and potentiated platelet aggregation at high shear rate in all patients. Because platelet aggregation at high shear rate requires vWf, the effect of DDAVP is probably due to the induced increase in plasma vWf. Therefore, platelet aggregation at high shear rate is defective in patients with congenital defects of platelet secretion and is potentiated by DDAVP. Potentiation of platelet aggregation at high shear rate may be one mechanism by which DDAVP shortens the prolonged bleeding time of patients with congenital defects of platelet secretion.

Shear-induced platelet aggregation is potentiated by desmopressin and inhibited by ticlopidine

Shear-induced platelet aggregation is important in physiological hemostasis and in the pathogenesis of arterial thrombosis. It requires extracellular Ca2+, platelet membrane glycoproteins Ib/IX and IIb/IIIa, von Willebrand factor (vWF), and ADP. We studied the effects of desmopressin (DDAVP), which increases plasma vWF levels and shortens the bleeding time, and of ticlopidine, which inhibits platelet responses to ADP, on shear-induced platelet aggregation. Eleven healthy volunteers were given oral ticlopidine (250 mg b.i.d.) for 7 days. The same subjects were infused intravenously with DDAVP (0.3 micrograms/kg body wt) before the first and after the last doses of ticlopidine. The degree of platelet aggregation induced by shear stress at 25, 50, 75, and 100 dyne/cm2 in a cone-and-plate viscometer, plasma vWF levels, and the bleeding time were measured before and after each DDAVP infusion. Plasma vWF levels and the extent of shear-induced platelet aggregation increased after DDAVP and were correlated. Ticlopidine partially inhibited shear-induced platelet aggregation both before and after DDAVP infusion. The bleeding time, prolonged by ticlopidine, was shortened by DDAVP. Potentiation by DDAVP of shear-induced platelet aggregation may be one mechanism by which the drug shortens the prolonged bleeding time. Since shear-induced platelet aggregation can cause thrombotic occlusions in stenotic arterial vessels, our findings may explain the therapeutic efficacy of ticlopidine in arterial thrombosis.

Identification of a new congenital defect of platelet function characterized by severe impairment of platelet responses to adenosine diphosphate

This study characterizes a congenital hemorrhagic disorder caused by a platelet function defect with the following features: (1) severely impaired platelet aggregation and fibrinogen or von Willebrand factor (vWF) binding induced by adenosine diphosphate (ADP); (2) defective aggregation, release reaction, and fibrinogen or vWF binding induced by other agonists; (3) normal aggregation and release reaction induced by high concentrations of thrombin or collagen; (4) no further inhibition by ADP scavengers of aggregation, release reaction, and fibrinogen or vWF binding, comparable with those observed for normal platelets in the presence of ADP scavengers; (5) normal membrane glycoprotein (GP) composition and normal binding of the anti-GP IIb/IIIa monoclonal antibody 10E5; (6) no acceleration by ADP of binding of the anti-GP IIb/IIIa monoclonal antibody 7E3; (7) normal platelet-fibrin clot retraction if induced by thrombin or reptilase plus epinephrine, absent if induced by reptilase plus ADP; (8) no inhibition by ADP of the prostaglandin E1-induced increase in platelet cyclic adenosine monophosphate, but normal inhibition by epinephrine; (9) defective mobilization of cytoplasmic Ca2+ by ADP; (10) normal binding of 14C-ADP to fresh platelets, but defective binding of [2-3H]-ADP to formalin-fixed platelets. This congenital platelet function defect is characterized by selective impairment of platelet responses to ADP, caused by either decreased number of platelet ADP receptors or abnormalities of the signal-transduction pathway of platelet activation by ADP.

Sustained correction of the bleeding time in an afibrinogenaemic patient after infusion of fresh frozen plasma

We have evaluated the duration of the effect of replacement therapy with two different doses of fibrinogen on the prolonged bleeding time of an afibrinogenaemic patient and the relationship between changes in bleeding time and plasma and platelet fibrinogen concentrations. The infusion of 40 mg/kg fibrinogen, as fresh frozen plasma (FFP), corrected the prolonged bleeding time of the patient from longer that 30 min to 8 min. The bleeding time was still normal 9 d after infusion, at a time when the plasma and platelet fibrinogen levels were low (0.13 g/l and 27 micrograms/10(9) platelets; normal ranges 1.6-4.0 and 60-190). Two months later, the infusion of a smaller dose of fibrinogen (4 mg/kg) also corrected the bleeding time, which remained normal until the second day after infusion, despite the fact that plasma and platelet fibrinogen were very low (0.02 g/l and 3.4 micrograms/10(9) platelets). The bleeding time returned to the prolonged baseline values only by day 6 post-infusion, when plasma and platelet fibrinogen levels were 4 x 10(-4) g/l and 1.4 micrograms/10(9) platelets. Therefore, sustained correction of the prolonged bleeding time may be obtained in afibrinogenaemic patients with a single infusion of fibrinogen at lower doses than usually recommended.

Ticlopidine selectively inhibits human platelet responses to adenosine diphosphate

Platelet aggregation and fibrinogen binding were studied in 15 individuals before and 7 days after the oral administration of ticlopidine (250 mg b.i.d.). Ticlopidine significantly inhibited platelet aggregation induced by adenosine diphosphate (ADP), the endoperoxide analogue U46619, collagen or low concentrations of thrombin, but did not inhibit platelet aggregation induced by epinephrine or high concentrations of thrombin. Ticlopidine inhibited 125I-fibrinogen binding induced by ADP, U46619 or thrombin (1 U/ml). The ADP scavengers apyrase or CP/CPK, added in vitro to platelet suspensions obtained before ticlopidine, caused the same pattern of aggregation and 125I-fibrinogen binding inhibition as did ticlopidine. Ticlopidine did not inhibit further platelet aggregation and 125I-fibrinogen binding induced in the presence of ADP scavengers. After ticlopidine administration, thrombin or U46619, but not ADP, increased the binding rate of the anti-GPII b/III a monoclonal antibody 7E3 to platelets. Ticlopidine inhibited clot retraction induced by reptilase plus ADP, but not that induced by thrombin or by reptilase plus epinephrine, and prevented the inhibitory effect of ADP, but not that of epinephrine, on the PGE1-induced increase in platelet cyclic AMP. The number of high- and low-affinity binding sites for 3H-ADP on formalin-fixed platelets and their Kd were not modified by ticlopidine. These findings indicate that ticlopidine selectively inhibits platelet responses to ADP.

In vitro effects of picotamide on human platelet aggregation, the release reaction and thromboxane B2 production

We studied the in vitro effects of picotamide (N,N' bis 3 picolyl-4-methoxy-isophthalamide) on human platelet aggregation, the release reaction and the production of thromboxane B2 (TxB2) induced by several platelet agonists. The effects of picotamide were compared to those of acetylsalicylic acid (ASA). Picotamide (0.5 mmol/l) inhibited platelet aggregation, the release of ATP and TxB2 production induced by ADP, arachidonic acid (AA), collagen or the prostaglandin endoperoxide (PE) analogue U46619. ASA (0.5 mmol/l) did not affect platelet aggregation and the release of ATP induced by U46619. Picotamide and ASA inhibited the AA-induced platelet TxB2 production both under stirring and non-stirring conditions, whereas the pure thromboxane A2 receptor antagonist BM13177 (0.5 mmol/l) was inhibitory only under stirring conditions. Since under non-stirring conditions platelet aggregation does not occur, picotamide directly inhibits TxB2 production, whereas BM13177 inhibits the potentiation of TxB2 production due to TxA2/PE-dependent platelet aggregation. Malondialdehyde (MDA) production by unstirred platelets stimulated with AA was not significantly inhibited by picotamide. In conclusion, picotamide inhibits the TxA2/PE-dependent platelet responses to agonists by a double mechanism: (i), TxA2/PE antagonism; (ii) inhibition of thromboxane synthase.

Released adenosine diphosphate stabilizes thrombin-induced human platelet aggregates

Normal human platelets aggregated by thrombin undergo the release reaction and are not readily deaggregated by the combination of inhibitors hirudin, chymotrypsin, and prostaglandin E1 (PGE1). In contrast, thrombin-induced aggregates of platelets from patients with delta-storage pool deficiency (delta-SPD), which lack releasable nucleotides, are readily deaggregated by the same combination of inhibitors. The ease with which delta-SPD platelets are deaggregated is caused by the lack of stabilizing effects of released ADP, since: (1) exogenous adenosine diphosphate (ADP) (10 mumol/L), but not serotonin (2 mumol/L), abolishes the ability of these inhibitors to deaggregate delta-SPD platelets; (2) thrombin-induced aggregates of platelets from a patient (V.R.) (whose platelets have a severe, selective impairment of sensitivity to ADP, but normal amounts of releasable nucleotides) can be readily deaggregated, and addition of ADP does not stabilize the platelet aggregates; (3) apyrase or creatine phosphate (CP)/creatine phosphokinase (CPK), added before thrombin, make control platelets more easily deaggregated by hirudin, chymotrypsin, and PGE1, and do not change the deaggregation response of delta-SPD platelets and of V.R.'s platelets. Thrombin-induced aggregation and release of beta-thromboglobulin in control, delta-SPD, and in V.R.'s platelets was similar and not inhibited by apyrase or CP/CPK. The stabilizing effect of ADP on platelet aggregates is specific, since epinephrine in the presence of apyrase to remove traces of released ADP does not stabilize the aggregates of control, delta-SPD, or of V.R.'s platelets. Because epinephrine increases fibrinogen binding to thrombin-stimulated platelets to a greater extent than ADP, but does not stabilize the aggregates, it is unlikely that the additional fibrinogen binding sites induced by ADP have a major role in inhibiting deaggregation by the combination of inhibitors.

Fibrinogen-independent aggregation and deaggregation of human platelets: studies in two afibrinogenemic patients

Platelets from two afibrinogenemic patients were used to determine whether fibrinogen is essential for platelet aggregation and to examine whether released fibrinogen contributes to the stabilization of platelet aggregates when platelets have been induced to aggregate and release their granule contents by stimulation with thrombin. The addition of adenosine diphosphate (ADP) to platelet-rich plasma (PRP) or to suspensions of washed platelets from the afibrinogenemic patients caused the formation of small aggregates, which was either not inhibited or only slightly inhibited by the F(ab')2 fragments of an antibody to fibrinogen but was inhibited by an antibody (10E5) to glycoprotein IIb/IIIa. Thus there is a component of ADP-induced platelet aggregation that is not dependent on fibrinogen or other plasma proteins but is dependent on glycoprotein IIb/IIIa. There was little difference in the extent of aggregation and the release of granule contents of normal and afibrinogenemic platelets in response to the release-inducing agents collagen, platelet-activating factor (PAF), sodium arachidonate, or thrombin. With normal or afibrinogenemic platelets, aggregation by thrombin (0.2 U/mL or higher) was not inhibited by the F(ab')2 fragments of an antibody to human fibrinogen. Deaggregation by combinations of inhibitors of platelets aggregated by 1 U/mL thrombin showed no difference between platelets from afibrinogenemic and control subjects, indicating that released fibrinogen does not make a major contribution to the stabilization of platelet aggregates formed by thrombin stimulation.

In vitro and ex vivo effects of indobufen on human platelet aggregation, the release reaction and thromboxane B2 production

We have done a comprehensive study in normal volunteers of the in vitro and ex vivo effects of the antiplatelet agent indobufen on platelet aggregation, the release reaction and thromboxane B2 (TxB2) production as induced by different concentrations of aggregating agents. At low concentrations (10 microM), indobufen completely inhibited secondary platelet aggregation, the release reaction and TxB2 production stimulated by ADP, epinephrine and low concentrations of platelet-activating factor (PAF acether). Higher concentrations of indobufen (100 microM) completely inhibited TxB2 production, platelet aggregation and ATP release induced by arachidonic acid (1 mM) or collagen (2 micrograms/ml). The inhibitory effect was partially overcome by higher concentrations of arachidonic acid (2 mM). Data obtained ex vivo 2 h after the oral administration of 200 mg indobufen to 8 normal volunteers were in keeping with those of the in vitro study. We conclude that indobufen inhibits platelet aggregation and the release reaction by inhibiting the platelet arachidonate pathway.