Ristocetin-induced Platelet Aggregation Research Articles

Balancing the Expression and Production of a Heterodimeric Protein: Recombinant Agkisacutacin as a Novel Antithrombotic Drug Candidate

Agkisacucetin extracted from the venom of Agkistrodon acutus has been demonstrated to be a promising antithrombotic drug candidate in clinical studies due to its function as a novel platelet membrane glycoprotein (GP) Ib inhibitor. Agkisacucetin is a heterodimeric protein composed of α- and β-subunits with seven disulphide bonds. Both subunits form inactive homodimeric products, which cause difficulties for recombinant production. In this study, Agkisacucetin α- and β-subunits were inserted sequentially into the chromosome of Pichia pastoris at the mutant histidinol dehydrogenase gene and ribosomal DNA repeat sites, respectively. By optimizing the gene copies and productivity of each subunit by drug screening, we successfully obtained a recombinant strain with balanced expression of the two subunits. Using this strain, a yield greater than 100 mg/L recombinant Agkisacucetin in fed-batch fermentation was reached. The recombinant Agkisacucetin possessed extremely similar binding affinity to recombinant GPIb and human platelets in in vitro assays, and its ristocetin-induced platelet aggregation activity ex vivo was identical to that of the extracted native Agkisacucetin, demonstrating that the yeast-derived Agkisacucetin could be an effective alternative to native Agkisacucetin. Moreover, this study provides an effective strategy for balancing the expression and production of heterodimeric proteins in P. pastoris.

A Study on the Safety of Liver Biopsy Inpatients with Von Willebrand’s Disease

Objectives: Liver biopsy remains the gold standard for diagnosis of chronic liver diseases. Outpatient percutaneous biopsy is generally safe with a mortality rate of 0.17% and hospitalization rate for bleeding of 3%. Von Willebrand disease (vWD) syndrome is the most common inherited hematological disorder with a prevalence of 1% - 3% globally. We sought to study whether vWD increases the risk of bleeding for liver biopsies. Methods: All patients (n = 120) who underwent outpatient percutaneous liver biopsies from 1997 to 2007 were analyzed. Demographics, PT/INR, platelet count, vW antigen and ristocetin induced platelet aggregation were studied. Results: No vWD patients had major bleeding that required transfusion, hospitalization or surgery but 9 (75%) had minor local bleeding and all had ecchymosis, which resolved spontaneously within 24 hours. Conclusions: Patients with vW factor deficiency can undergo percutaneous liver biopsy without major bleeding. Minor bleeding may occur at a slightly higher rate. vWD is not a contraindication to percutaneous liver biopsy.

Laboratory Assessment of Anti-Coagulant Properties of a Von Willebrand Factor Targeted Aptamer

Introduction: Many cardiovascular procedures including percutaneous coronary intervention, coronary bypass surgery, and peripheral vascular surgery require antithrombotic therapy during the procedure. Heparin is frequently used, due to low cost, ease of monitoring and reversibility with protamine. Antiplatelet agents such as aspirin and clopidogrel are also frequently used but these agents are not reversible. Alternative reversible antithrombotic strategies that interfere with platelet-mediated thrombosis are needed. We are investigating the use of a reversible agent that is specific for von Willebrand factor (VWF) for use during cardiovascular procedures.We previously developed an antidote-controlled 80 oligonucleotide RNA aptamer Ch-9.14-T10 (T10). (Nimjee, S.M., Lohrmann, Wang, H, et al. Molecular Therapy 2012; 2:391-397). T10 bound to VWF with high affinity and inhibited thrombosis in a murine carotid artery damage model. The aptamer also greatly increased bleeding in mice that were surgically challenged by tail transection and blood loss decreased when complementary antidote oligonucleotides were administered. In addition, T10 inhibited primary hemostasis in the PFA-100 assay and this inhibition was completely reversed by the antidote. This study further characterizes the T10 aptamer, as well as a truncated version of the T10 aptamer, using clinical laboratory assays that would be used to monitor antithrombotic therapies during cardiovascular procedures.Methods: We initiated our study with T10 and then developed a truncated version, T25, a 60 oligonucleotide with which we performed additional investigations. We recruited normal donors for analysis of aptamer and antidotes. All participants had normal platelet counts, VWF activity and antigen levels, and were not taking antiplatelet agents. Laboratory tests included: ristocetin induced platelet agglutination (RIPA), VWF activity, ristocetin cofactor activity, cone and plate(let) analyzer, thromboelastography (TEG) and thromboelastometry (ROTEM).Results: We first determined the effects of the VWF aptamers on RIPA, VWF activity, and ristocetin cofactor activity to confirm functional inhibition of VWF. We found that T10 (500-750 nM) and T25 (250-750nM) completely inhibited RIPA depending on the donor. T25 also inhibited VWF activity with a Ki of 160-320 nM and ristocetin cofactor activity with an IC50 of 3000 nM. Employing a cone and plate(let) analyzer we found that T25 (750 nm) reduced platelet adhesion by 33-49% on a polystyrene surface under arterial flow conditions (1800 s-1, for 2 minutes). The aggregate size was also reduced by 30%.As ACT and TEG are frequently used during cardiovascular procedures, we performed several measures with our VWF aptamer. T10 had no effect on the ACT (730-2000nM), TEG (1600 nM), or ROTEM (750 nM). Standard methods were used for the TEG (Kaolin activation followed by CaCl2) and ROTEM (EXTEM assay) Topf et al. reported a modified ROTEM protocol where they found that incubating citrated whole blood with ristocetin decreased the clot strength as measured by the maximum amplitude (Thromb.Haemost 2011; 105:1091). We reasoned that an aptamer that bound to VWF would inhibit the effect of ristocetin on the maximum amplitude. We found that T25 did inhibit the effect of ristocetin and titration studies showed that 200-400 nM T25 was needed to restore the maximum amplitude to at least 80% of its original value. An example of the ROTEM tracings is shown in figure 1.Conclusion: The VWF-specific aptamer T25 can be detected by several clinical assays, including the RIPA, VWF activity assays, and the cone and plate(let) analyzer. It is not detectable by an ACT or standard TEG or ROTEM, however. We are able to detect the aptamer using a modified ROTEM and are further defining the adaptability of this assay to facilitate monitoring during cardiovascular procedures.Citrated whole blood from was incubated with buffer or ristocetin (0.7 mg/ml) or ristocetin and T25 (300 nM) as indicated. Clotting was initiated with EXTEM (tissue factor pathway activation) and CaCl2. [Display omitted] DisclosuresBecker:Regado Biosciences: Membership on an entity’s Board of Directors or advisory committees.

Clinical and laboratory diagnosis of VWD.

VWD is the most common inherited bleeding disorder and is due to a deficiency and/or abnormality of VWF. VWD is inherited in an autosomal-dominant or autosomal-recessive pattern, but women are apparently more symptomatic. Three main criteria are required for correct diagnoses of VWD: (1) positive bleeding history since childhood, (2) reduced VWF activity in plasma, and (3) history of bleeding in the family. The bleeding score, together with baseline VWF levels and family history, have been proposed as more evidence-based criteria for VWD. Measurements of a reduced VWF activity in plasma are essential for the diagnosis of VWD; assays for the evaluation of the interactions between VWF and platelet glycoprotein Ib receptor with or without ristocetin, as well as VWF collagen binding, are currently in use. However, other tests such as VWF antigen, factor VIII, ristocetin-induced platelet agglutination, multimeric analysis, VWF propeptide, VWF/FVIII binding assay, and assessment of biological response to desmopressin are necessary to characterize VWD types. Levels of VWF activities <30 U/dL have been associated with a bleeding phenotype and the presence of mutations in the VWF gene.

Assessment of platelet function with light transmission aggregometry in 24 patients supported with a continuous-flow left ventricular assist device: A single-center experience

This study evaluated platelet function for an extended period of time in patients with a HeartMate II continuous-flow left ventricular assist device (Thoratec Corporation, Pleasanton, Calif) with light transmission aggregometry and investigated the potential role of this test in clinical management. Twenty-four patients were studied prospectively after implantation. Mean duration of support was 8.5 months. Platelet functions were assessed with light transmission aggregometry induced by thrombin receptor agonist peptide, ristocetin, or arachidonic acid. All patients received an aspirin regimen that was progressively increased until arachidonic acid-triggered platelet aggregation dropped lower than 20%. Plasma levels of von Willebrand factor were also determined when ristocetin-induced platelet agglutination was impaired. Intensity of platelet aggregation with thrombin receptor agonist peptide was little changed in patients with a HeartMate II relative to control subjects. Aspirin dose greater than 160 mg/d was progressively required in 46% of patients. Ristocetin-induced platelet agglutination was impaired in 4 patients in association with a lack of high molecular weight von Willebrand factor multimers. Three patients had thromboembolic events (12.5%) and 8 (33%) suffered from major bleeding complications. High platelet reactivity during treatment with aspirin is common in patients with a HeartMate II. Moreover, light transmission aggregometry may detect impaired ristocetin-induced platelet agglutination, enabling dosage of aspirin to be adjusted. Our strategy showed no major improvements in terms of thrombosis rate when compared with published data, although bleeding frequency was somewhat reduced. Benefits of light transmission aggregometry testing need to be assessed in a larger randomized study with a longer follow-up.

Abstract 499: Development of a Novel Antithrombotic Therapy Targeting Platelet GPIbα: Assessment of Anfibatide In Vitro and in Phase I Clinical Trial

Platelet adhesion and aggregation are critical for hemostasis and atherothrombosis. Interaction between the GPIb complex and VWF initiates platelet adhesion and contributes to complete vessel occlusion, particularly at sites of stenosis. However, no therapeutic targeting this pathway has been developed. Previously, we demonstrated in murine thrombosis models that Anfibatide, a snake venom-derived GPIbα antagonist, inhibited botrocetin-induced VWF-GPIbα binding and inhibited thrombus formation in vitro and in vivo, without significantly activating platelets or changing bleeding. We subsequently hypothesized that Anfibatide would be a safe and potent anti-thrombotic agent in humans. We tested Anfibatide with human platelets in vitro and conducted the first anti-GPIbα phase I clinical trial with 94 healthy volunteers. In vitro, Anfibatide inhibited ristocetin-induced and low dose thrombin-induced human platelet aggregation. Surface plasmon resonance studies showed that Anfibatide binds to GPIbα and blocks binding of both VWF A1 domain and thrombin. In ex vivo perfusion chambers, Anfibatide strongly inhibited human platelet adhesion, aggregation, and thrombus formation on a collagen-coated surface, especially at high shear flow conditions. Importantly, Anfibatide effectively dissolved the preformed thrombi in perfusion chambers. Anfibatide incubation with human whole blood did not significantly change coagulation parameters measured by thromboelastography. After treating volunteers with Anfibatide, no serious adverse events, premature discontinuations due to adverse events, or deaths occurred during the study. Anfibatide bound to 95% of GPIb and inhibited 90% of platelet aggregation without prolonging activated partial thromboplastin time, prothrombin time, thrombin time, or bleeding time. There was no bleeding tendency, no alteration of platelet count, and no detectable anti-Anfibatide antibodies. In conclusion, Anfibatide provides anti-thrombotic effects through inhibition of both GPIbα-VWF and GPIbα-thrombin interactions. These results demonstrate that Anfibatide is a safe and potent anti-platelet reagent with great potential for future anti-thrombotic therapy.

Enhanced platelet apoptosis in chronic uremic patients

Background: There is a paucity of research on platelet apoptosis and its contribution to platelet dysfunction in uremic patients. The present study sought to analyze platelets apoptosis in uremic patients who underwent different dialysis modalities. Methods: Sixteen chronic uremic patients (5 on hemodialysis, 6 on peritoneal dialysis and 5 on non-dialysis) and 16 controls were studied. Platelet-rich plasma was detected for apoptotic events including depolarization of mitochondrial inner membrane potential (ΔΨm), phosphatidylserine (PS) exposure, activation of caspases-3 and Bcl-2 family proteins variations by Flow Cytometry or by Western-Blot. Washed normal platelets were incubated with normal or uremic platelet poor plasma and then were detected apoptotic events. Platelets function was assessed by ristocetin induced aggregative function test. Results: Compared to controls, uremic platelets demonstrated greater apoptosis for the ΔΨm depolarization (43.48 ± 9.58 vs. 52.76 ± 15.36, p = 0.005) as well as PS exposure (1.36 ± 0.51 vs. 0.99 ± 0.27, p < 0.001). There was no significant difference among different treatment groups (for the ΔΨm depolarization f = 0.16, p = 0.85; for the PS exposure f = 1.06, p = 0.36). Western Blot analyses showed caspase-3 activation and pro-apoptotic Bcl-2 family proteins expression. Platelets exposed to uremic plasma exhibited distinct apoptosis phenomena. Ristocetin induced platelet aggregation was markedly diminished in uremic patients and treated platelets. Conclusions: These findings indicate that platelets are incurred apoptosis in uremia patients. Uremic plasma accelerates apoptosis of normal platelets, resulting in a dysfunctional pattern of platelets in uremia. Uremic platelets apoptosis has no relationship with dialysis modality.

Platelet-Type von Willebrand Disease: Toward an Improved Understanding of the “Sticky Situation”

We are pleased to highlight in this issue of Seminars in Thrombosis & Hemostasis, the study by Wood et al,1 wherein the authors describe a novel mutation in the platelet GP1BA gene creating a hyperresponsive GPIbα protein—a receptor for von Willebrand factor (VWF)—and causing platelet-type von Willebrand disease (PT-VWD). This is a new naturally occurring mutation in a 23-year-old male patient and is considered the sixth reported mutation thus far in patients described with this disease worldwide. Despite being a rare bleeding disorder, PT-VWD represents a significant challenging clinical problem as it may cause life-threatening bleeding, if not appropriately treated, particularly in situations related to surgeries and childbirth. The clinical diagnosis challenge stems from the close similarity of PT-VWD to the more common bleeding disorder, type 2BVWD.2,3 The discrimination and correct diagnosis can only be made after carefully assessing less commonly performed laboratory tests,3–8 and confirmed only after DNA analysis of the binding regions in the two genes VWF and GP1BA9 has been performed. The report by Woods et al1 highlights some important issues that add to our understanding of this rare but potentially life-threatening bleeding disorder. First, the patient presented with severe bleeding symptoms (rather than mild/moderate bleeding symptoms, and unlike previously reported cases) while also showing other typical laboratory phenotypic data known in this disease such as macrothrombocytopenia, mild spontaneous platelet aggregation, absence from plasma of high-molecular-weight VWF multimers, positive ristocetin-induced platelet aggregation (RIPA) at 0.3 and 0.4 mg/mL, VWF ristocetin cofactor (VWF:RCo) T GP1BA gene mutation that predicted the protein change Try246Leu. This mutation was absent in the unaffected mother and also in 100 healthy control subjects. Second, in that report,1 an attempt was made to quantify the bleeding symptoms in a patient with PT-VWD (bleeding score of 13). The knowledge about variation in bleeding symptoms and the ability to objectively assess these symptoms have proven to be important inmanagement of bleeding disorders and can help predict disease outcome and also aid in treatment.10 The only other such attempt was in a small case series reported recently. This series showed considerable variability in bleeding severity among PT-VWD that is independent of age or gender. The phenotypic variability in type 2B VWD has been reviewed in relation to various mutations and different patients’ cohorts.12 However, a systematic analysis of PT-VWD phenotype and the genotype–phenotype relationship remains to be investigated. Third, for the first time, the level of VWF propeptide (VWFpp) and VWFpp/VWF:Ag ratio was reported in a patient with PT-VWD.1 VWFpp is a 741 amino acid portion that gets cleaved from mature VWF by proteolysis. After cleavage, the VWFpp remains in noncovalent association with the VWF multimers, and both are stored together in the α-granules (megakaryocytes/platelets) or Weibel–Palade bodies (endothelial cells). Upon release and under physiologic pH, the VWF multimers and VWFpp dissociate and are secreted in 1:1 stoichiometric amounts.13 Studies have shown a regulatory role for VWFpp as an intramolecular chaperone for the mature VWF protein and an aid to its storage and multimerization.14,15 The VWFpp circulates in the plasma for a short time, with a half-life of approximately 2 to 3 hours and plasma levels of approximately 1 μg/mL, whereas multimeric VWF circulates with a half-life of approximately 8 to 12 hours and plasma levels of approximately 10 μg/mL.16,17 Recent

Identification of p.W246L As a Novel Mutation in the GP1BA Gene Responsible for Platelet-Type von Willebrand Disease

Platelet-type von Willebrand disease (PT-VWD) and type 2B von Willebrand disease (2B-VWD) are rare bleeding disorders characterized by increased ristocetin-induced platelet aggregation (RIPA) at low concentrations of ristocetin. Diagnosis of either condition is not easy and the differential diagnosis between the two entities is especially challenging as evidenced by high levels of misdiagnosis of both conditions, but particularly PT-VWD. Five mutations in the GP1BA gene related to PT-VWD and less than 50 patients are currently reported worldwide. We herein describe a patient with severe bleeding symptoms, macrothrombocytopenia, mild spontaneous platelet aggregation, positive RIPA at 0.3 and 0.4 mg/mL, von Willebrand factor ristocetin cofactor (VWF:RCo) to antigen (VWF:Ag) < 0.2, normal VWF propeptide/VWF:Ag ratio, and RIPA mixing tests and cryoprecipitate challenge positive for PT-VWD. GP1BA gene was studied in the patient, in his mother, and in 100 healthy control subjects. We identified a heterozygous substitution G > T located at nucleotide 3805 in the g.DNA of the patient's GP1BA gene, resulting in a Trp to Leu amino acid change at residue 246 (p.W246L). This mutation was absent in his unaffected mother and also in the 100 controls, and was predicted as damaging by in silico analysis. The residue W246 is located within the VWF-binding region and exists in a strongly conserved position in the phylogenetic tree, which is expected to be unable to tolerate substitutions without changing its functional characteristics. These findings argue strongly in favor of the view that this substitution does not represent a polymorphism and is therefore responsible for the PT-VWD phenotype of the patient.

As a Rare Disease Bernard–Soulier Syndrome in Differential Diagnosis of Immune Thrombocytopenic Purpura: A Case Report

Introduction: Bernard–Soulier syndrome is a rare autosomal recessive disease that causes a deficiency of glycoprotein Ib, the receptor for von Willebrand factor, which is important for clot formation. It is estimated to occur in fewer than 1 per 1 million persons. The differential diagnosis includes von Willebrand disease, immune thrombocytopenic purpura, May–Hegglin anomaly, thrombocytopenia-absent radius syndrome, grey platelet syndrome, and other inherited giant platelet disorders. Case Presentation: A 30-year-old Turkish woman was admitted to the Department of Heamatology for evaluation of thrombocytopenia. Because she had repeated epistaxis during admission, she was assessed to evaluate for haemorrhagic diathesis. She had been diagnosed with immune thrombocytopenic purpura and given steroid therapy at different times. Peripheral blood smear was characterized by neutrophils 75%, lymphocytes 20%, monocytes 5%, giant platelets and platelets forming three to four clusters, a normal red blood cell morphology. A decreased ristocetin-induced platelet aggregation was detected in low and high concentration. On the basis of these findings, Bernard–Soulier syndrome was screened with flow cytometry and genetic mutation. CD41a 86.2%, CD42a 92.9%, CD42b 92.5%, and CD61 87.8% were detected in flow cytometry. Normal platelet GPIb/IX levels by flow cytometry turned down the suspected diagnosis. genetic analysis, we have applied to our patient and her parents. We detected same mutation in patient and her mother. Laboratuar parameters and flow cytometry of mother did not support diagnosis of Bernard–Soulier syndrome. Conclusion: Bernard–Soulier syndrome should be considered before a young patient is diagnosed with immune thrombocytopenia purpura and peripheral blood smear should be examined for giant platelets.

The caspase-3 inhibitor (peptide Z-DEVD-FMK) affects the survival and function of platelets in platelet concentrate during storage

BackgroundAlthough apoptosis occurs in nucleated cells, studies show that this event also occurs in some anucleated cells such as platelets. During storage of platelets, the viability of platelets decreased, storage lesions were observed, and cells underwent apoptosis. We investigated the effects of caspase-3 inhibitor on the survival and function of platelets after different periods of storage.MethodsPlatelet concentrates were obtained from the Iranian Blood Transfusion Organization in plastic blood bags. Caspase-3 inhibitor (Z-DEVD-FMK) was added to the bags. These bags along with control bags to which no inhibitor was added were stored in a shaking incubator at 22℃ for 7 days. The effects of Z-DEVD-FMK on the functionality of platelets were analyzed by assessing their ability to bind to von Willebrand factor (vWF) and to aggregate in the presence of arachidonic acid and ristocetin. Cell survival was surveyed by MTT assay.ResultsAt day 4 of storage, ristocetin-induced platelet aggregation was significantly higher in the inhibitor-treated (test) than in control samples; the difference was not significant at day 7. There was no significant difference in arachidonic acid-induced platelet aggregation between test and control samples. However, at day 7 of storage, the binding of platelets to vWF was significantly higher in test than in control samples. The MTT assay revealed significantly higher viability in test than in control samples at both days of study.ConclusionTreatment of platelets with caspase-3 inhibitor could increase their functionality and survival.

Rapid purification of a new P-I class metalloproteinase from Bothrops moojeni venom with antiplatelet activity.

The present study aimed to evaluate the proteolytic and biological activities of a new metalloproteinase from B. moojeni venom. The purification of BmooMPα-II was carried out through two chromatographic steps (ion-exchange and affinity). BmooMPα-II is a monomeric protein with an apparent molecular mass of 22.5 kDa on SDS-PAGE 14% under nonreducing conditions. The N-terminal sequence (FSPRYIELVVVADHGMFTKYKSNLN) revealed homology with other snake venom metalloproteinases, mainly among P-I class. BmooMPα-II cleaves Aα-chain of fibrinogen followed by Bβ-chain, and does not show any effect on the γ-chain. Its optimum temperature and pH for the fibrinogenolytic activity were 30–50°C and pH 8, respectively. The inhibitory effects of EDTA and 1,10-phenantroline on the fibrinogenolytic activity suggest that BmooMPα-II is a metalloproteinase. This proteinase was devoid of haemorrhagic, coagulant, or anticoagulant activities. BmooMPα-II caused morphological alterations in liver, lung, kidney, and muscle of Swiss mice. The enzymatically active protein yet inhibited collagen, ADP, and ristocetin-induced platelet aggregation in a concentration-dependent manner. Our results suggest that BmooMPα-II contributes to the toxic effect of the envenomation and that more investigations to elucidate the mechanisms of inhibition of platelet aggregation may contribute to the studies of snake venom on thrombotic disorders.

Addition of in-vitro generated endothelial microparticles to von-Willebrand plasma improves primary and secondary hemostasis

Increased endothelial microparticles (EMP) as markers for endothelial activation have been associated with worse outcomes in clinical prothrombotic situations. The procoagulant properties of EMP can be attributed to the expression of phospholipids, tissue factor and von-Willebrand factor on their surface. We therefore investigated whether addition of in-vitro generated EMP modifies hemostasis in plasma from patients with severe von-Willebrand disease (VWD). A large EMP pool was obtained from stimulated endothelial cell lines and EMP concentration was quantified by flow cytometry. The influence of EMP on primary and secondary hemostasis in VWD plasma was assessed using ristocetin-induced platelet aggregation (RIPA) and thrombin generation in a calibrated automated thrombogram (CAT), respectively. After addition of EMP, there was a significant increase in the maximal aggregation level in RIPA as well as a significant shortening of lag time and time-to-peak in CAT in comparison to control buffer. In summary, in vitro-generated EMP have the potential to improve hemostasis in severe VWD plasma and these results warrant further clinical reseach regarding their contribution to the clinical bleeding phenotype as well as their potential to improve replacement therapy.

Adenovirus type 3 induces platelet activation in vitro

In the present study, we aimed to investigate platelet activation induced by adenovirus type 3 (HAdV3) invitro. Platelet-rich plasma (PRP) or whole blood was incubated with or without HAdV at various concentrations. Platelet aggregation, platelet counting, fibrinogen and expression of platelet membrane antigens (CD41a and CD62P) were determined following incubation with HAdV for different periods of time. The results demonstrated that HAdV at the concentrations of 109-1011vp/ml enhanced adenosine diphosphate (ADP) or ristocetin-induced platelet aggregation, however did not alter the platelet count. Infection with HAdVs also reduced fibrinogen level. P-selectin and CD41a appeared rapidly on the surface after platelets were incubated with HAdVs invitro for 30min. In conclusion, HAdVs may induce activation of platelets and lead to a pre-thrombotic state of peripheral blood. This finding may aid in the development of measures to prevent severe HAdV infection.

Anti-platelet activity of a three-finger toxin (3FTx) from Indian monocled cobra (Naja kaouthia) venom

A low molecular weight anti-platelet peptide (6.9kDa) has been purified from Naja kaouthia venom and was named KT-6.9. MALDI-TOF/TOF mass spectrometry analysis revealed the homology of KT-6.9 peptide sequence with many three finger toxin family members. KT-6.9 inhibited human platelet aggregation process in a dose dependent manner. It has inhibited ADP, thrombin and arachidonic acid induced platelet aggregation process in dose dependent manner, but did not inhibit collagen and ristocetin induced platelet aggregation. Strong inhibition (70%) of the ADP induced platelet aggregation by KT-6.9 suggests competition with ADP for its receptors on platelet surface. Anti-platelet activity of KT-6.9 was found to be 25 times stronger than that of anti-platelet drug clopidogrel. Binding of KT-6.9 to platelet surface was confirmed by surface plasma resonance analysis using BIAcore X100. Binding was also observed by a modified sandwich ELISA method using anti-KT-6.9 antibodies. KT-6.9 is probably the first 3FTx from Indian monocled cobra venom reported as a platelet aggregation inhibitor.

Quick Recertification Series

Quick Recertification Series

Novel Bernard-Soulier syndrome variants caused by compound heterozygous mutations (case I) or a cytoplasmic tail truncation (case II) of GPIbα

A defective platelet glycoprotein (GP) Ib/IX/V complex [von Willebrand factor (VWF) receptor] results in Bernard-Soulier syndrome (BSS), which is characterized by macrothrombocytopenia and impaired ristocetin- and thrombin-induced platelet aggregation. We found 2 independent BSS-variant families: Case I [compound heterozygous mutations, p.Glu331X and a frame shift by a deletion at c.1444delA of GPIbα (GP1BA) terminating at a premature stop codon (p.Thr452ProfsX58)], and case II [homozygous nonsense mutation at c.1723C>T, p.Gln545X]. Case I platelets expressed no GPIbα, resulting in absence of ristocetin-induced platelet aggregation (RIPA) and 50% reduction in thrombin-induced aggregation with no shape change. The mother's platelets had 50% the expression level of A-type GPIbα (4-repeated VNTR: variable number of tandem repeats, p.[Thr145Met; Ser399_Pro411[4]]); the father's platelets had the same expression level of C-type GPIbα (2-repeated VNTR, p.Ser399_Pro411dup) as the mother's platelets. The mother's RIPA was significantly higher than the father's. Thrombin-induced aggregation was normal in both parents. Case II platelets expressed a GPIbα with an abnormal cytoplasmic tail, p.Gln545X-truncated GPIbα, which complexed with GPIX and GPV on the cell surface; its expression level of the complex was normal. Case II platelets had reversible RIPA, with no ATP release, and weak thrombin-induced aggregation without shape change. These results suggest that a signaling process through the GPIbα cytoplasmic tail required for full platelet activation is defective in BSS variant case II and a length polymorphism of GPIbα is associated with a modified level of RIPA heterozygous BSS case I.

Acquired von Willebrand syndrome

Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder that mimics the inherited form of von Willebrand disease (VWD) in terms of laboratory findings and clinical presentation. To study the etiology of acquired VWD. The patients referred from various hospitals in and out of Mumbai were included in the study. Six patients with AVWS diagnosed at this center over the last 10 years were analyzed against 171 patients with inherited VWD. The differential diagnosis of AVWS was made based on reduced levels of von Willebrand antigen and von Willebrand ristocetin cofactor, decrease in ristocetin induced platelet aggregation, absence of correction in mixing studies with no prior history of bleeding problems and a negative family history for bleeding disorders. In three patients, the disease was associated with systematic lupus erythematosus, out of which one was also associated with Kikuchi lymphadenitis and second with autoimmune hemolytic anemia. Fourth case was associated with hypothyroidism and fifth was a case of dermatitis and vitiligo. The last patient was a case of hemophilia A with Burkitts lymphoma, who developed autoantibodies to von Willebrand factor. Except two patients, all other patients responded to immune suppressive therapy with corticosteroids, while the patient with hypothyroidism responded to oral thyroxine. AVWS is a rare condition and may often be missed or diagnosed as inherited disease associated with heterogeneous disease conditions.

Primary hemostatic capacity of whole blood: a comprehensive analysis of pathogen reduction and refrigeration effects over time

Whole blood (WB) has been used in combat since World War I as it is readily available and replaces every element of shed blood. Component therapy has become standard; however, recent military successes with WB resuscitation have revived the debate regarding wider WB use. Characterization of optimal WB storage is needed. We hypothesized that refrigeration preserves WB function and that a pathogen reduction technology (PRT) based on riboflavin and ultraviolet light has no deleterious effect over 21 days of storage. WB units were stored for 21 days either at 4°C or 22°C. Half of each temperature group underwent PRT, yielding four final treatment groups (n = 8 each): CON 4 (WB at 4°C); CON 22 (WB at 22°C); PRT 4 (PRT WB at 4°C); and PRT 22 (PRT WB at 22°C). Testing was at baseline, Days 1-7, 10, 14, and 21. Assays included coagulation factors; platelet activation, aggregation, and adhesion; and thromboelastography (TEG). Prothrombin time (PT) and partial thromboplastin time increased over time; refrigeration attenuated the effects on PT (p ≤ 0.009). Aggregation decreased over time (p ≤ 0.001); losses were attenuated by refrigeration (p ≤ 0.001). Refrigeration preserved TEG parameters (p ≤ 0.001) and PRT 4 samples remained within normal limits throughout the study. Refrigeration in combination with PRT inhibited fibrinolysis (p ≤ 0.001) and microparticle formation (p ≤ 0.031). Cold storage increased shear-induced platelet aggregation and ristocetin-induced platelet agglutination (p ≥ 0.032), as well as GPIb-expressing platelets (p ≤ 0.009). The in vitro hemostatic function of WB is largely unaffected by PRT treatment and better preserved by cold storage over 21 days. Refrigerated PRT WB may be suitable for trauma resuscitation. Clinical studies are warranted.

Effect of statins on platelet function in patients with hyperlipidemia

IntroductionIt is generally assumed that cholesterol reduction by statins is the predominant therapeutic result underlying their beneficial effects in cardiovascular disease. However, the action of statins may be partially independent of their effects on plasma cholesterol levels, as they combine lipid lowering with positive effects on hemorheological conditions and endothelial function. We evaluated the impact of statin treatment on platelet adhesion to fibrinogen (spontaneous and ADP-activated), along with ADP, collagen or ristocetin-induced aggregation in type II hyperlipidemic patients.Material and methodsThe study group included 70 persons: 50 patients affected by type II hyperlipidemia without concomitant diseases and 20 healthy volunteers. The effects of 8-week statin treatment (atorvastatin 10 mg/day, simvastatin 20 mg/day, or pravastatin 20 mg/day) on platelet activation were evaluated.ResultsRegardless of the type of statin, a significant decrease in ADP-induced platelet aggregation was observed: for atorvastatin 50.6 ±12.8% vs. 41.1 ±15.8% (p < 0.05), for simvastatin 57.2 ±18.0% vs. 44.7 ±22.1% (p = 0.05), and for pravastatin 55.8 ±19.5% vs. 38.8 ±23.3% (p < 0.05). There was no significant effect of statins on collagen or ristocetin-induced platelet aggregation and adhesion.ConclusionsTherapy with statins beneficially modifies ADP-induced platelet aggregation in patients with hyperlipidemia and does not affect spontaneous or ADP-induced platelet adhesion to fibrinogen and platelet aggregation induced by collagen or ristocetin.