Differential effects of anticoagulants on the activation of platelets ex vivo

Development of a super-hydrophilic anaerobic tube for the optimization of platelet-rich fibrin

Horizontal platelet-rich fibrin (H-PRF) contains a variety of bioactive growth factors and cytokines that play a key role in the process of tissue healing and regeneration. The blood collection tubes used to produce Solid-PRF (plasmatrix (PM) tubes) have previously been shown to have a great impact on the morphology, strength and composition of the final H-PRF clot. Therefore, modification to PM tubes is an important step toward the future optimization of PRF. To this end, we innovatively modified the inner wall surface of the PM tubes with plasma and adjusted the gas environment inside the PM tubes to prepare super-hydrophilic anaerobic plasmatrix tubes (SHAP tubes). It was made anaerobic for the preparation of H-PRF with the aim of improving mechanical strength and bioactivity. The findings demonstrated that an anaerobic environment stimulated platelet activation within the PRF tubes. After compression, the prepared H-PRF membrane formed a fibrous cross-linked network with high fracture strength, ideal degradation characteristics, in addition to a significant increase in size. Thereafter, the H-PRF membranes prepared by the SHAP tubes significantly promoted collagen synthesis of gingival fibroblast and the mineralization of osteoblasts while maintaining excellent biocompatibility, and advantageous antibacterial properties. In conclusion, the newly modified PRF tubes had better platelet activation properties leading to better mechanical strength, a longer degradation period, and better regenerative properties in oral cell types including gingival fibroblast and alveolar osteoblasts. It also improves the success rate of H-PRF preparation in patients with coagulation dysfunction and expands the clinical application scenario.

Mepacrine Flow Cytometry Assay for the Diagnosis of Platelet δ-granule Defects: Literature Review on Methods-Towards a Shared Detailed Protocol

Accurate assessment of platelet secretion is essential for the diagnosis of inherited or acquired platelet function disorders and more specifically in identifying δ-storage pool disease. Mepacrine, a fluorescent dye, specifically accumulates in platelet δ-granules. The mepacrine flow cytometry (mepacrine FCM) assay has been used for more than half a century in the clinical laboratory as a diagnostic tool for platelet δ-granule disorders. The assay requires a small volume of blood, can be performed in thrombocytopenic patients, provides rapid assessment of δ-granule content and secretion, and, thus, enables differentiation between storage and release defects. There is however a broad heterogeneity in methods, reagents, and equipment used. Lack of standardization and limited data on analytical and clinical performances have led the 2022 ISTH SSC (International Society on Thrombosis and Haemostasis Scientific and Standardization Committee) Subcommittee on Platelet Physiology expert consensus to rate this assay as simple but of uncertain value. Yet, the data used by experts to formulate the recommendations were not discussed and even not mentioned. Guidance for laboratory studies of platelet secretion assay would be very helpful for clinical laboratories and health authorities especially considering the implications of the new In Vitro Diagnostic Regulation in Europe. The purpose of the present work was to review the reported methodologies for the mepacrine FCM assay and to offer an example of detailed protocol. This would help standardization and pave the way for more rigorous comparative studies.

Peripheral blood to next-generation sequencing ready DNA library: a novel engineering design for automation

Whole genome sequencing (WGS) has become a gold standard for diagnosing genomic variation. Peripheral blood is a common sample source for the extraction of nucleic acids for Next-Generation Sequencing (NGS) applications. Here, we present an integrated and fully automated device design that uses new concepts of fluid mechanics, heat-mass transfer, and thermodynamics of enzymatic reactions to extract nucleic acids from the blood and perform DNA library preparation from a pre-filled plate. We demonstrate that the presented device effectively extracts dsDNA with an average of 25.03 µg/mL and 25.91 µg/mL yield from citrate-stabilized human peripheral blood stored in Fresh (4 °C) and Frozen (-20 °C) conditions, respectively. Furthermore, our method automatically extracts nucleic acids and creates a high-quality sequence-ready DNA library from blood stabilized with citrate and EDTA for 8 samples simultaneously in a single run with a total operation time of ~ 7 h. Our results show the required coverage and depth of the genome, highlighting an essential application of this device in processing blood samples for genome sequencing.

Assessing prognosis by quantifying FcγRIIa on fixed platelets

Introduction: FcγRIIa amplifies platelet activation and higher platelet FcγRIIa identifies patients at greater risk of subsequent cardiovascular events. We report the accuracy and precision of a modified test to quantify FcγRIIa on previously fixed platelets (pFCG test).Methods & results: An antibody clone (5G1) was developed after exposure of mice to formaldehyde treated FcγRIIa. Accuracy and precision of the modified test was evaluated with biologic specimens (platelets) and engineered synthetic cells conjugated with FcγRIIa (Slingshot Biosciences). The modified pFCG test on fixed platelets (using 5G1) consistently identified modestly more (∼300 molecules) of FcγRIIa on platelets compared with the pFCG test on nonfixed platelets (using clone FL18.26). With biologic specimens, the intra-assay coefficient of variation (CV) was 2.1 ± 0.1% (standard error of the mean, n = 750). The interassay CV was assessed intraday (4.5 ± 1%) and interday (up to 5 days after fixation, 6.5 ± 0.4%, n = 50). The pFCG test performed on Slingshot Synthetic cells conjugated with FcγRIIa demonstrated accuracy, linearity (R2 = 0.984) and similar interassay CV both intraday (2% ± 0.6%) and interday (20 nonconsecutive days, 9.9% ± 2.1%).Conclusion: In summary, modification of the pFCG test to be performed on fixed platelets allows accurate quantification of pFCG with high precision.

Point-of-Care Testing in Patients with Hereditary Disorders of Primary Hemostasis: A Narrative Review

Inherited disorders of primary hemostasis, such as von Willebrand disease and congenital platelet disorders, can cause extensive, typically mucocutaneous bleeding. Assays to diagnose and monitor these disorders, such as von Willebrand factor activity assays and light transmission aggregometry, are performed in specialized hemostasis laboratories but are commonly not available in local hospitals. Due to the complexity and relative scarcity of these conventional assays, point-of-care tests (POCT) might be an attractive alternative in patients with hereditary bleeding disorders. POCTs, such as thromboelastography, are increasingly used to assess hemostasis in patients with acquired hemostatic defects, aiding clinical decision-making in critical situations, such as during surgery or childbirth. In comparison, the use of these assays in patients with hereditary hemostasis defects remains relatively unexplored. This review aims to give an overview of point-of-care hemostasis tests in patients with hereditary disorders of primary hemostasis. A summary of the literature reporting on the performance of currently available and experimental POCTs in these disorders is given, and the potential utility of the assays in various use scenarios is discussed. Altogether, the studies included in this review reveal that several POCTs are capable of identifying and monitoring severe defects in the primary hemostasis, while a POCT that can reliably detect milder defects of primary hemostasis is currently lacking. A better understanding of the strengths and limitations of POCTs in assessing hereditary defects of primary hemostasis is needed, after which these tests may become available for clinical practice, potentially targeting a large group of patients with milder defects of primary hemostasis.

Platelet FcγRIIA: An emerging regulator and biomarker in cardiovascular disease and cancer

Platelets, anucleate blood cells derive from megakaryocytes, are involved in cardiovascular diseases and tumors. FcγRIIA, the only FcγR expressed on human platelets, is known for its role in immune-related diseases. A growing body of evidence reveals that platelet FcγRIIA is a potential target for the prevention and control of cardiovascular disease and cancer, and is an advantageous biomarker. In this review, we describe the structure and physiological function of platelet FcγRIIA, its regulatory role in cardiovascular disease and cancer, and its potential clinical application.

Preanalytical conditions for multiparameter platelet flow cytometry

Background

Flow cytometry is an important technique for understanding multiple aspects of blood platelet biology. Despite the widespread use of the platform for assessing platelet function, the optimization and careful consideration of preanalytical conditions, sample processing techniques, and data analysis strategies should be regularly assessed. When set up and designed with optimal conditions, it can ensure the acquisition of robust and reproducible flow cytometry data. However, these parameters are rarely described despite their importance.

Objectives

We aimed to characterize the effects of several preanalytical variables on the analysis of blood platelets by multiparameter fluorescent flow cytometry.

Methods

We assessed anticoagulant choice, sample material, sample processing, and storage times on 4 distinct and commonly used markers of platelet activation, including fibrinogen binding, expression of CD62P and CD42b, and phosphatidylserine exposure.

Results

The use of suboptimal conditions led to increases in basal platelet activity and reduced sensitivities to stimulation; however, the use of optimal conditions protected the platelets from artifactual stimulation and preserved basal activity and sensitivity to activation.

Conclusion

The optimal preanalytical conditions identified here for the measurement of platelet phenotype by flow cytometry suggest a framework for future development of multiparameter platelet assays for high-quality data sets and advanced analysis.

BDNF as a biomarker for neuropathic pain: Consideration of mechanisms of action and associated measurement challenges

INTRODUCTION

The primary objective of this paper is to (1) provide a summary of human studies that have used brain derived neurotrophic factor (BDNF) as a biomarker, (2) review animal studies that help to elucidate the mechanistic involvement of BDNF in the development and maintenance of neuropathic pain (NP), and (3) provide a critique of the existing measurement techniques to highlight the limitations of the methods utilized to quantify BDNF in different biofluids in the blood (i.e., serum and plasma) with the intention of presenting a case for the most reliable and valid technique. Lastly, this review also explores potential moderators that can influence the measurement of BDNF and provides recommendations to standardize its quantification to reduce the inconsistencies across studies.

METHODS

In this manuscript we examined the literature on BDNF, focusing on its role as a biomarker, its mechanism of action in NP, and critically analyzed its measurement in serum and plasma to identify factors that contribute to the discrepancy in results between plasma and serum BDNF values.

RESULTS

A large heterogenous literature was reviewed that detailed BDNF's utility as a potential biomarker in healthy volunteers, patients with chronic pain, and patients with neuropsychiatric disorders but demonstrated inconsistent findings. The literature provides insight into the mechanism of action of BDNF at different levels of the central nervous system using animal studies. We identified multiple factors that influence the measurement of BDNF in serum and plasma and based on current evidence, we recommend assessing serum BDNF levels to quantify peripheral BDNF as they are more stable and sensitive to changes than plasma BDNF.

CONCLUSION

Although mechanistic studies clearly explain the role of BDNF, results from human studies are inconsistent. More studies are needed to evaluate the methodological challenges in using serum BDNF as a biomarker in NP.

Impact of surface coating and systemic anticoagulants on hemostasis and inflammation in a human whole blood model

BACKGROUND

Surface compatibility with blood is critical both for scientific investigations on hemostasis and clinical applications. Regarding in vitro and ex vivo investigations, minimal alteration in physiological hemostasis is of particular importance to draw reliable conclusions on the human coagulation system. At the same time, artificial coagulation activation must be avoided, which is relevant for the patient, for example to prevent stent graft occlusion. The aim was to evaluate the advantages and disadvantages of antithrombotic and antifouling surface coatings in the context of their suitability for ex vivo incubation and the study of coagulation properties.

METHODS

We investigated the impact of different protocols for surface coating of synthetic material and different anticoagulants on hemostasis and platelet activation in ex vivo human whole blood. Blood samples from healthy donors were incubated in coated microtubes on a rotating wheel at 37°C. Two protocols for surface coating were analyzed for hemostatic parameters and metabolic status, a heparin-based coating (CHC, Corline Heparin Conjugate) without further anticoagulation and a passivating coating (MPC, 2-methacryloyloxethyl phosphorylcholine) with added anticoagulants (enoxaparin, ENOX; or fondaparinux, FPX). Employing the MPC-based coating, the anticoagulants enoxaparin and fondaparinux were compared regarding their differential effects on plasmatic coagulation by thrombelastometry and on platelet activation by flowcytometry and platelet function assays.

RESULTS

Using the CHC coating, significant coagulation cascade activation was observed, whereas parameters remained mostly unchanged with MPC-based protocols. Extended incubation caused significantly elevated levels of the soluble membrane attack complex. Neither ENOX nor FPX caused a relevant impairment of platelet function or activation capacity and thrombelastometric parameters remained unchanged with both protocols. For translational purposes, we additionally modeled endotoxemia with the MPC-based protocols by incubating with lipopolysaccharide plus/minus thrombin. While coagulation parameters remained unchanged, elevated Interleukin 8 and Matrix Metalloproteinase 9 demonstrated preserved immune cell responsiveness.

CONCLUSIONS

The MPC-based protocols demonstrated better hemocompatibility compared to CHC, and ENOX and FPX proved useful for additional anticoagulation. Furthermore, this simple-to-use whole blood model may be useful for experimental analyses of the early coagulatory and immunological response without decalcification.

Non-cardiac surgery in patients with coronary artery disease: risk evaluation and periprocedural management

Perioperative cardiovascular complications are important causes of morbidity and mortality associated with non-cardiac surgery, particularly in patients with coronary artery disease (CAD). Although preoperative cardiac risk assessment can facilitate the identification of vulnerable patients and implementation of adequate preventive measures, excessive evaluation might lead to undue resource utilization and surgical delay. Owing to conflicting data, there remains some uncertainty regarding the most beneficial perioperative strategy for patients with CAD. Antithrombotic agents are the cornerstone of secondary prevention of ischaemic events but substantially increase the risk of bleeding. Given that 5-25% of patients undergoing coronary stent implantation require non-cardiac surgery within 2 years, surgery is the most common reason for premature cessation of dual antiplatelet therapy. Perioperative management of antiplatelet therapy, which necessitates concomitant evaluation of the individual thrombotic and bleeding risks related to both clinical and procedural factors, poses a recurring dilemma in clinical practice. Current guidelines do not provide detailed recommendations on this topic, and the optimal approach in these patients is yet to be determined. This Review summarizes the current data guiding preoperative risk stratification as well as periprocedural management of patients with CAD undergoing non-cardiac surgery, including those treated with stents.

Variation in platelet expression of FcγRIIa after myocardial infarction

FcγRIIa amplifies platelet activation and greater platelet expression of FcγRIIa identifies patients at greater risk of subsequent cardiovascular events. Thus, platelet expression of FcγRIIa may be useful to guide therapy. Because platelet function tests are impacted by preparative procedures and substantial intra-individual variability, we examined the impact of these factors on platelet expression of FcγRIIa in blood from healthy subjects and in patients after myocardial infarction (MI). Platelet expression of FcγRIIa was quantified with the use of flow cytometry. Blood was taken from healthy subjects and 114 patients after a MI in whom platelet expression of FcγRIIa was quantified before discharge and at 6 ± 1 months. Neither anticoagulants nor the antiplatelet agent cangrelor changed platelet expression of FcγRIIa. Intra-individual variation in platelet FcγRIIa expression was 8.5% ± 5% over the course of 1 month in healthy subjects. Platelet FcγRIIa expression was within 20% of the baseline value after 6 months in 71% of patients after MI. In summary, because FcγRIIa is a protein on the surface of platelets, assay conditions and antiplatelet agents do not change expression. Intra-individual variability in platelet expression of FcγRIIa is modest. Accordingly, platelet expression of FcγRIIa is a marker of increased platelet reactivity that can be reliably and repeatedly measured.Clinical Trial Registration: NCT02505217.

Vascular Endothelial Growth Factor Levels in Serum and Plasma following Esophageal Cancer Resection - Relationship to Platelet Count

In patients with cancer circulating vascular endothelial growth factor (VEGF) may be tumor-derived and have prognostic significance. Activated platelets may also be a source of VEGF, releasing it in serum formation. Debate exists as to whether serum or plasma VEGF (S-VEGF, P-VEGF) is the most appropriate surrogate marker of tumor angiogenesis. As healing wounds produce VEGF that can spill over into the circulation, we aimed to investigate the potential confounding effects of cancer surgery on both perioperative S-VEGF and P-VEGF levels and to evaluate their relationship with platelet count. S-VEGF, P-VEGF and platelet counts were measured in 23 patients undergoing esophageal cancer resection. Samples were taken preoperatively and six weeks following surgery. Seven patients were also sampled on postoperative days 1, 5 and 10. VEGF was assayed using a commercial enzyme linked immunosorbent assay. S-VEGF and P-VEGF both rose after surgery (S-VEGF; day 5: 1017 [446–1224] pg/mL and day 10: 1231 [626–2046] pg/mL versus pre-op: 329 [189–599] pg/mL. P-VEGF; day 1: 55 [46–104] pg/mL and day 10: 58 [20–154] pg/mL versus pre-op: 23 [13–46] pg/mL), falling towards pre-operative levels by six weeks. Platelet count correlated with S-VEGF (rho=0.281; p<0.05, Spearman's rank) and P-VEGF (rho=0.330; p<0.01, Spearman's rank). Platelets may contribute to VEGF levels in plasma as well as in serum. The effects of surgery on S-VEGF or P-VEGF levels are mainly transient. Care must be exercised when interpreting circulating VEGF levels in the early postoperative period.

Influence of erythrocyte aggregation on radial migration of platelet-sized spherical particles in shear flow

Blood platelets when activated are involved in the mechanisms of hemostasis and thrombosis, and their migration toward injured vascular endothelium necessitates interaction with red blood cells (RBCs). Rheology co-factors such as a high hematocrit and a high shear rate are known to promote platelet mass transport toward the vessel wall. Hemodynamic conditions promoting RBC aggregation may also favor platelet migration, particularly in the venous system at low shear rates. The aim of this study was to confirm experimentally the impact of RBC aggregation on platelet-sized micro particle migration in a Couette flow apparatus. Biotin coated micro particles were mixed with saline or blood with different aggregation tendencies, at two shear rates of 2 and 10s^-1 and three hematocrits ranging from 20 to 60%. Streptavidin membranes were respectively positioned on the Couette static and rotating cylinders upon which the number of adhered fluorescent particles was quantified. The platelet-sized particle adhesion on both walls was progressively enhanced by increasing the hematocrit (p<0.001), reducing the shear rate (p<0.001), and rising the aggregation of RBCs (p<0.001). Particle count was minimum on the stationary cylinder when suspended in saline at 2s^-1 (57±33), and maximum on the rotating cylinder at 60% hematocrit, 2s^-1 and the maximum dextran-induced RBC aggregation (2840±152). This fundamental study is confirming recent hypotheses on the role of RBC aggregation on venous thrombosis, and may guide molecular imaging protocols requiring injecting active labeled micro particles in the venous flow system to probe human diseases.

The effect of centrifugation speed and time on pre-analytical platelet activation

BACKGROUND

The results of laboratory analyses are affected by pre-analytical variables, and in particular can platelets be activated by shear handling stress and secrete granular substances. We therefore evaluated the effect of centrifugation speed and time on pre-analytical platelet activation.

METHODS

Citrate- and EDTA-anticoagulated blood from healthy volunteers were centrifuged at 80-10,000 g for 5-15 min to prepare plasma and platelet-rich plasma. Pre-analytical platelet activation was assessed by flow cytometric measurement of platelet P-selectin (CD62p) expression. Blood cell counts, mean platelet volume (MPV), immature platelet fraction (IPF), and platelet distribution width (PDW) were measured. Platelet aggregation in platelet-rich plasma induced by arachidonic acid (AA), ADP or thrombin receptor activator peptide-6 (TRAP) was tested by 96-well aggregometry.

RESULTS

The median percentage of platelets expressing P-selectin in citrate- and EDTA-plasma centrifuged at 2000 g for 10 min were 43% [interquartile range (IQR), 38%-53%] and 56% (IQR, 31%-78%), respectively (p=0.82). Platelet-rich plasma prepared at 100-250 g for 10 min had significantly lower platelet P-selectin expression (11%-15%), p<0.001. Platelet count in plasma samples decreased with increasing speed but platelets were only completely removed if plasma was re-centrifuged. In platelet-rich plasma, increasing centrifugation speed significantly increased platelet yield but decreased contamination from other blood cells, platelet composition was altered as platelet parameters (MPV, IPF, and PDW) was lowered. Platelet aggregation was not affected by the centrifugation speed platelet-rich plasma was prepared.

CONCLUSIONS

Proportional to centrifugation speed, platelets in plasma and platelet-rich plasma were activated with centrifugation speed, cell content and composition changed while platelet aggregation was unaltered.

Platelet Activation in Bypass Surgery for Critical Limb Ischemia

Platelet activation contributes to graft occlusion after bypass surgery. This study investigated platelet activation status before, during, and after bypass. Blood was taken preoperatively from patients undergoing femoro-popliteal bypass and at incision, after dissection, after ischemia, after reperfusion, 24 hours after surgery, and almost 2 years after bypass (and given aspirin or warfarin). Platelet aggregation was measured using a turbidimetric method and platelet activation with flow cytometry. Statistical analysis was performed using Mann-Whitney U and Wilcoxon's tests. Resting platelet activation was similar between controls and patients undergoing bypass. Platelet activation decreased at incision but remained highly reactive. Platelet aggregation increased after dissection and the ischemic phase but significantly decreased after reperfusion. Platelet aggregation and activation were increased at 24 hours and subsequently after bypass. Platelets in critical limb ischemia exist in the primed state and become activated by minimum stimuli. Increased platelet activation occurs after bypass grafting for critical limb ischemia despite adjunctive therapy.

Impact of timing from blood sampling to pharmacodynamic assessment on measures of platelet reactivity in patients treated with P2Y12 receptor inhibitors

Several platelet function tests (PFT) are available to assess the pharmacodynamic (PD) effects of P2Y₁₂ inhibitors. However, there are technical variances between PFT, and P2Y₁₂ inhibitors differ in pharmacological properties. Manufactures of PFT recommend a time-frame within which assessments needs to be executed. However, if the timing from blood sampling to processing affects PD results is unknown. We conducted a prospective study assessing the impact of timing from blood sampling to processing on PD measures using three different PFT. We studied 60 aspirin-treated patients with coronary artery disease (CAD) on maintenance P2Y₁₂ inhibiting therapy [clopidogrel 75 mg/day (n=20), prasugrel 10 mg/day (n=20) and ticagrelor 90 mg bid (n=20)]. PD assessments (trough levels) were performed by VerifyNow P2Y12 (VN), light transmittance aggregometry (LTA) and vasodilator-stimulated phosphoprotein (VASP) at 30 minutes, 2 and 4 hours post-sampling; VASP was also performed at 24 hours. P2Y₁₂ reaction units (PRU) by VN significantly decreased over time with all P2Y₁₂ inhibitors (clopidogrel p<0.001; prasugrel p=0.016; ticagrelor p<0.001). PRU at 30 minutes and 2 hours were similar, but decreased at 4 hours. LTA showed consistent findings with VN. Conversely, PD measures as assessed by VASP were stable over time (p>0.1 for all P2Y₁₂ inhibitors). In conclusion, in CAD patients on maintenance therapy with P2Y₁₂ inhibitors, timing from blood sampling to processing significantly influences PD measures as assessed by VN and LTA, but not by VASP.

Stirred, shaken, or stagnant: What goes on at the blood-biomaterial interface

There is a widely recognized need to improve the performance of vascular implants and external medical devices that come into contact with blood by reducing adverse reactions they cause, such as thrombosis and inflammation. These reactions lead to major adverse cardiovascular events such as heart attacks and strokes. Currently, they are managed therapeutically. This need remains unmet by the biomaterials research community. Recognized stagnation of the blood-biomaterial interface research translates into waning interest from clinicians, funding agencies, and practitioners of adjacent fields. The purpose of this contribution is to stir things up. It follows the 2014 BloodSurf meeting (74th International IUVSTA Workshop on Blood-Biomaterial Interactions), offers reflections on the situation in the field, and a three-pronged strategy integrating different perspectives on the biological mechanisms underlying blood-biomaterial interactions. The success of this strategy depends on reengaging clinicians and on the renewed cooperation of the funding agencies to support long-term efforts.

Methodological considerations to determine the effect of exercise on brain-derived neurotrophic factor levels

OBJECTIVES

Physical exercise up-regulates brain-derived neurotrophic factor (BDNF) in the brain and blood. However, there is yet no consensus about the adequate blood processing conditions to standardize its assessment. We aimed to find a reliable blood sample processing method to determine changes in BDNF due to exercise.

DESIGN AND METHODS

Twelve healthy university students performed an incremental cycling test to exhaustion. At baseline, immediately after exercise, and 30 and 60 min of recovery, venous blood was drawn and processed under different conditions, i.e. whole blood, serum coagulated for 10 min and 24 h, total plasma, and platelet-free plasma. BDNF concentration was measured by ELISA.

RESULTS

Exercise increased BDNF in whole blood and in serum coagulated for 24 h when corrected by hemoconcentration. We did not find effects of exercise on BDNF in serum coagulated for 10 min or in plasma samples. Plasma shows heterogeneous BDNF values in response to exercise that are not prevented when platelets are eliminated while homogeneous BDNF levels were found in whole blood or serum coagulated for 24 hour samples.

CONCLUSIONS

In exercise studies, BDNF levels should be adjusted by hemoconcentration. Our data highlight the importance of blood sample selection since the differences between each one affect significantly the BDNF factor changes due to exercise.

Reference range determination for whole-blood platelet aggregation using the Multiplate analyzer

OBJECTIVES

To develop reference ranges for platelet aggregation using the Multiplate analyzer (Roche Diagnostics, Mannheim, Germany) in blood anticoagulated with sodium citrate (Na-citrate), lithium heparin (Li-heparin), or hirudin.

METHODS

The study was performed at three sites on consented, healthy adults (n = 193) not taking antiplatelet medication. Platelet aggregation was evaluated in response to adenosine-5'-diphosphate, arachidonic acid, collagen, thrombin receptor activating peptide, ristocetin, and adenosine-5'-diphosphate combined with prostaglandin E1. Precision testing was conducted using healthy donors and donors taking aspirin.

RESULTS

Whole-blood platelet aggregation showed anticoagulant-dependent differences in platelet responses to all agonists. Samples collected in Na-citrate demonstrated the lowest responses to all agonists. The highest responses were obtained using Li-heparin. Precision testing revealed high variability in platelet aggregation at lower agonist doses, regardless of anticoagulant. Highest platelet response variations occurred in response to arachidonic acid in blood anticoagulated with hirudin from participants taking aspirin.

CONCLUSIONS

These data demonstrate the importance of establishing locally relevant reference ranges.

The effect of corn trypsin inhibitor and inhibiting antibodies for FXIa and FXIIa on coagulation of plasma and whole blood

BACKGROUND

Corn trypsin inhibitor (CTI), an inhibitor of FXIIa, is used to prevent plasma coagulation by contact activation, to specifically investigate tissue factor (TF)-initiated coagulation.

OBJECTIVE

In the present work the specificity of CTI for factor (F) XIIa is questioned.

METHODS AND RESULTS

In the commercial available plasma coagulation assays CTI was found to double activated partial thromboplastin time (APTT) at a plasma concentration of 7.3 ± 1.5 μm CTI (assay concentration 2.4 μm). No effect was found on the prothrombin time (PT) when high TF concentrations were used. Also, with specific antibodies for FXIIa and for FXIa only APTT was found to be extended but not PT. With specific enzyme assays using chromogenic substrates CTI was shown to be a strong inhibitor of FXIIa and a competitive inhibitor of FXIa with Ki  = 8.1 ± 0.3 μm, without effect on the coagulation factors FVIIa, FIXa, FXa and thrombin. In thrombin generation and coagulation (free oscillation rheometry, FOR) assays, initiated with low TF concentrations, no effect of CTI (plasma concentrations of 4.4 and 13.6 μm CTI, 25 resp. 100 mg L(-1) in blood) was found with ≥ 1 pm TF. At ≤ 0.1 pm TF in the FOR whole blood assay the coagulation time (CT) concentration dependently increased while the plasma CT became longer than the observation time.

CONCLUSION

To avoid inhibition of FXIa and the thrombin feedback loop we recommend that for coagulation assays the concentration of CTI in blood should be below 20 mg L(-1) (1.6 μm) and in plasma below 3 μm.

Effects on platelet function of a direct acting antagonist of coagulation factor Xa

Because novel direct acting anticoagulants are being tested in the secondary prevention of cardiovascular events, we assessed potential effects of a direct acting antagonist of Factor Xa on platelet function. Blood from patients with known coronary artery disease who were treated with aspirin but no other antithrombotic agent was spiked in vitro with rivaroxaban alone or in combination with a direct acting P2Y12 antagonist (cangrelor). To limit cofounding effects of anticoagulants and to enable interaction between coagulation factors, blood was anticoagulated only with a specific inhibitor of Factor XIIa, corn trypsin inhibitor. Polymerization of fibrin was prevented with the peptide GPRP. Activation of platelets was determined with the use of flow cytometry in response to lipidated tissue factor, thrombin, the collagen mimetic convulxin, and adenosine diphosphate (ADP). Rivaroxaban inhibited the activation of platelets induced by tissue factor and to a lesser extent activation induced by thrombin, effects that were accentuated when combined with cangrelor. Rivaroxaban did not attenuate convulxin-induced activation of platelets; however, a limited but consistent attenuation of ADP-induced platelet activation was seen with blood anticoagulated with rivaroxaban. Effects of rivaroxaban on ADP-induced platelet activation were not mediated by thrombin, tissue factor, or platelet-leukocyte aggregation. In conclusion, rivaroxaban attenuated in vitro the activation of platelets mediated by thrombin. In light of the pivotal role of thrombin in platelet activation after rupture of an atherosclerotic plaque, rivaroxaban should attenuate platelet activation in vivo, an effect that is accentuated by combination with a P2Y12 antagonist.

The effect of selected pre-analytical phase variables on plasma thromboxane A₂ measurements in humans

AIMS

Platelet function testing is often affected by the existence of different pre-analytical variables that can cause platelet activation. The aim of this study was to assess the effect of such variables that are present when samples are taken (different anticoagulants, incubation temperature, and storage conditions) to select those which enable to reach optimal range of measured plasma concentrations of the two stable thromboxane A₂ metabolites, that is, thromboxane B₂ (TxB₂) and 11-dehydrothromboxane B₂ (11-dTxB₂).

MATERIALS AND METHODS

For the purpose of this study, whole blood samples obtained from 20 volunteers were screened for TxB₂ and 11-dTxB₂ concentrations using commercial EIA kits (Cayman Chemicals™; Neogen™) in relation to the effect of different anticoagulants, using different incubation temperatures and storage conditions.

RESULTS

Trisodium citrate has been shown not to be affecting the TxB₂ and 11-dTxB₂ concentrations compared with the values measured in the serum. Incubation of the samples for 1 h at 37 °C and freezing at -20 °C or -80 °C give the most suitable concentration range of both thromboxanes in the used EIA measurement.

CONCLUSION

This study describes the setup of such pre-analytical phase conditions that enable the screening of platelet function in terms of the plasma concentrations of TxB₂ and 11-dTxB₂ in selected EIA measurement.

Enhanced soluble expression of recombinant Flavobacterium heparinum heparinase I in Escherichia coli by fusing it with various soluble partners

Heparinase I (HepA) was originally isolated from Flavobacterium heparinum (F. heparinum) and specifically cleaves heparin/heparan sulfate in a site-dependent manner, showing great promise for producing low molecular weight heparin (LMWH). However, expressing recombinant HepA is extremely difficult in Escherichia coli because it suffers from low yields, insufficient purity and insolubility. In this paper, we systematically cloned and fused the HepA gene to the C-terminus of five soluble partners, including translation initiation factor 2 domain I (IF2), glutathione S-transferase (GST), maltose-binding protein (MBP), small ubiquitin modifying protein (SUMO) and N-utilization substance A (NusA), to screen for their abilities to improve the solubility of recombinant HepA when expressed in E. coli. A convenient two-step immobilized metal affinity chromatography (IMAC) method was utilized to purify these fused HepA hybrids. We show that, except for NusA, the fusion partners dramatically improved the soluble expression of recombinant HepA, with IF2-HepA and SUMO-HepA creating almost completely soluble HepA (98% and 94% of expressed HepA fusions are soluble, respectively), which is the highest yield rate published to the best of our knowledge. Moreover, all of the fusion proteins show comparable biological activity to their unfused counterparts and could be used directly without removing the fusion tags. Together, our results provide a viable option to produce large amounts of soluble and active recombinant HepA for manufacturing.

Anti-platelet therapy: glycoprotein IIb-IIIa antagonists

Glycoprotein (GP) IIb-IIIa antagonists inhibit the aggregation of activated platelets. Three agents are approved for clinical use. In this review, the characteristics of each agent, their pharmacodynamic profile, results in pivotal clinical trials and the associated clinical implications are discussed. GP IIb-IIIa antagonists have greatest benefit when used as adjunctive therapy during percutaneous coronary intervention (PCI) when the patient has intra-coronary thrombosis. These agents appear to provide greatest benefit when used in combination with heparin. The clinical niche for parenteral GP IIb-IIIa antagonists is evolving. The rapid onset and offset of GP IIb-IIIa antagonists plus dosing designed to inhibit extensively platelet aggregation differentiates them from oral agents. The contemporary niche appears to include patients in transition, such as individuals requiring emergent PCI before oral agents are fully active and for unstable patients requiring transport to PCI centres, particularly in patients likely to have intracoronary thrombus. Subsequent studies should evaluate the optimal duration of therapy with GP IIb-IIIa antagonists.

Heparin but not citrate anticoagulation of blood preserves platelet function for prolonged periods

BACKGROUND

Current guidelines state that platelet aggregation studies should be conducted within 4 h of venepuncture because of the decline in sensitivity to platelet agonists. This constrains studies of platelet activity in clinical situations where samples need to be transported or there are unavoidable delays prior to assessment.

OBJECTIVES

The aim of the present study was to compare systematically the responses of platelets stored in the presence of either citrate or heparin, the two most widely used anti-coagulants, using a range of standard techniques.

METHODS

Blood was taken from healthy volunteers and either assessed immediately or stored at ambient temperature (18-25 degrees C) for 24 h. Platelet reactivity to a range of agonists was determined by a combination of 96-well plate techniques; light transmission aggregometry, thrombi adhesion, ATP and ADP release, and TxA(2) release; by whole blood aggregometry; and by PFA-100.

RESULTS AND CONCLUSIONS

Testing using 96-well plate techniques allowed for the simultaneous measurement of responses to multiple concentrations of multiple agonists. The responses of platelets from blood anti-coagulated with heparin were predominantly preserved in all assays after 24 h storage, whereas, responses of platelets stored in blood anti-coagulated with citrate were greatly diminished. Consequently, anti-coagulation with heparin, but not citrate, preserves platelet responses for up to 24 h as determined by a range of techniques.

Association between increased platelet P-selectin expression and obesity in patients with type 2 diabetes: a BARI 2D (Bypass Angioplasty Revascularization Investigation 2 Diabetes) substudy

OBJECTIVE

To determine whether obesity increases platelet reactivity and thrombin activity in patients with type 2 diabetes plus stable coronary artery disease.

RESEARCH DESIGN AND METHODS

We assessed platelet reactivity and markers of thrombin generation and activity in 193 patients from nine clinical sites of the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D). Blood taken at the time of enrollment was used for assay of the concentration of prothrombin fragment 1.2 (PT1.2, released when prothrombin is activated) and fibrinopeptide A (FPA, released when fibrinogen is cleaved). Platelet activation was identified with the use of flow cytometry in response to 0, 0.2, and 1 micromol/l adenosine diphosphate (ADP).

RESULTS

Concentrations of FPA, PT1.2, and platelet activation in the absence of agonist were low. Greater BMI was associated with higher platelet reactivity in response to 1 microm ADP as assessed by surface expression of P-selectin (r = 0.29, P < 0.0001) but not reflected by the binding of fibrinogen to activated glycoprotein IIb-IIIa. BMI was not associated with concentrations of FPA or PT1.2. Platelet reactivity correlated negatively with A1C (P < 0.04), was not related to the concentration of triglycerides in blood, and did not correlate with the concentration of C-reactive peptide. CONCLUSIONS Among patients enrolled in this substudy of BARI 2D, a greater BMI was associated with higher platelet reactivity at the time of enrollment. Our results suggest that obesity and insulin resistance that accompanies obesity may influence platelet reactivity in patients with type 2 diabetes.

The effect of ex vivo anticoagulants on whole blood platelet aggregation

Pre- and intraoperative platelet function monitoring is increasingly recommended in order to detect risk factors for bleeding and to target coagulation management. The ideal anticoagulant for accurate platelet aggregometry remains controversial. The aim of this experimental trial was to compare platelet aggregability in whole blood stored in citrate, heparin and direct thrombin inhibitors. Whole blood was drawn from 11 healthy adult volunteers who had not taken any medication in the previous 14 days. Blood was stored in trisodium citrate, unfractionated heparin, melagatran, lepirudin and argatroban. Platelet aggregation was performed using the impedance aggregometer Multiplate (Dynabyte, Munich, Germany) with adenosine diphosphate (ADP), thrombin receptor activating peptide (TRAP), collagen, arachidonic acid and ristocetin as agonists. Samples were analysed immediately after blood sampling (baseline), as well as 30 and 120 min afterwards. At baseline there were no significant differences in aggregability between samples containing direct thrombin inhibitors and heparin. In contrast, aggregation in response to all agonists except for ristocetin was significantly impaired in citrated blood. During storage the response to arachidonic acid and collagen was maintained by direct thrombin inhibitors and heparin, whereas ADP-, TRAP- and ristocetin-induced aggregation varied considerably over time in all ex vivo anticoagulants tested. Pre-analytical procedures should be standardized because storage duration and anticoagulants significantly affect platelet aggregability in whole blood. For point-of-care monitoring with immediate analysis after blood withdrawal all tested direct thrombin inhibitors as well as unfractionated heparin can be used as anticoagulants whereas citrate is not recommended.

Effects of enoxaparin and unfractionated heparin on platelet activity and reactivity during carotid endarterectomy

The aim of this study was to determine platelet activity and reactivity and the effects of unfractionated heparin (UFH) and enoxaparin on platelet function during carotid eversion endarterectomy under local anesthesia. Twenty symptomatic patients undergoing carotid endarterectomy were randomly assigned to either 5,000 units of UFH or body weight-adjusted enoxaparin (0.5 mg/kg body weight) as an intraoperative intravenous bolus. The activity of platelets was assessed by measuring the expression of CD62p and CD41 with flow cytometry. Additionally, platelet-leukocyte aggregates (PLAs) were enumerated. The reactivity of platelets was evaluated by measuring the expression of the same antigens after stimulation. In addition, platelet reactivity was also analyzed using a PFA-100 analyzer. A significant increase in platelet activity was observed during surgery for CD41 and CD62p (p = .002 and < .001, respectively). The number of PLAs showed no significant changes during surgery. Yet there was a significant difference between patients treated with UFH and patients treated with enoxaparin. No difference for platelet activity or reactivity for patients receiving either UFH or enoxaparin prior to cross-clamping of the carotid arteries was seen. The formation of PLAs after endarterectomy was significantly higher in the UFH group; thus, PLAs are probably a useful surrogate parameter for measuring platelet activity.

Influence of preparative procedures on assay of platelet function and apparent effects of antiplatelet agents

Previous studies have shown that anticoagulants alter platelet reactivity and the apparent effects of antiplatelet agents. This study was conducted to identify the impact of methods of preparation of blood samples on an assay of platelet function and the effects of antiplatelet agents. The activation of platelets was identified with the use of flow cytometry in response to thrombin (1 and 10 nmol/L), adenosine diphosphate (0.2 and 1 micromol/L), platelet activating factor (1 nmol/L), and convulxin (1 and 10 ng/ml). Antiplatelet effects were assessed after the addition in vitro of tirofiban (50 ng/ml) and cangrelor (10 nmol/L). Results were compared in whole blood and platelet-rich plasma (PRP) anticoagulated with corn trypsin inhibitor (32 microg/ml, a specific inhibitor of factor XIIa). The fraction of young platelets was quantified with thiazole orange, which identifies ribonucleic acid. The activation of platelets was consistently less in PRP compared with whole blood. Activation in PRP was 23 +/- 15% that in whole blood for thrombin, 65 +/- 26% for adenosine diphosphate, 40 +/- 20% for platelet activating factor, and 49 +/- 25% for convulxin (p <0.01 for each comparison). The fraction of young platelets in PRP was 39 +/- 11% that in whole blood (p <0.001). The effects of antiplatelet agents varied with agonist and antiplatelet agent but were generally greater in PRP compared with whole blood (p <0.05). In conclusion, platelet reactivity is lower and the effects of antiplatelet agents are greater and potentially misleading in PRP compared with whole blood. The accuracy of platelet function testing may be improved by performance in whole blood.

Increased platelet expression of FcGammaRIIa and its potential impact on platelet reactivity in patients with end stage renal disease

BACKGROUND

Increased platelet reactivity has been implicated in cardiovascular disease - the major cause of death in patients with end stage renal disease (ESRD). FcGammaRIIA is a component of glycoprotein VI and Ib-IX-V that mediate activation of platelets by collagen and von Willebrand factor. To determine whether expression of FcGammaRIIA impacts platelet reactivity we quantified its expression and platelet reactivity in 33 patients with ESRD who were undergoing hemodialysis.

METHODS

Blood samples were obtained from patients immediately before hemodialysis and before administration of heparin. Platelet expression of FcGammaRIIA and the activation of platelets in response to low concentrations of convulxin (1 ng/ml, selected to mimic effects of collagen), thrombin (1 nM), adenosine diphosphate (ADP, 0.2 microM), or platelet activating factor (PAF, 1 nM) were determined with the use of flow cytometry in samples of whole blood anticoagulated with corn trypsin inhibitor (a specific inhibitor of Factor XIIa).

RESULTS

Patients were stratified with respect to the median expression of FcGammaRIIA. Patients with high platelet expression of FcGammaRIIA exhibited 3-fold greater platelet reactivity compared with that in those with low expression in response to convulxin (p < 0.01) and 2-fold greater activation in response to thrombin, ADP, and PAF (p < 0.05 for each). For each agonist, expression of FcGammaRIIA correlated modestly but positively with platelet reactivity. The strongest correlation was with thrombin-induced activation (r = 0.6, p < 0.001).

CONCLUSION

Increased platelet reactivity in response to low concentrations of diverse agonists is associated with high expression of FcGammaRIIA and may contribute to an increased risk of thrombosis in patients with ESRD.

Greater inhibitory effects of bivalirudin compared with unfractionated heparin plus eptifibitide on thrombin-induced platelet activation

OBJECTIVES

The effects of antithrombotic agents on the activation of platelets by thrombin were determined in blood from patients (n=12) with symptomatic coronary artery disease.

METHODS

Blood obtained immediately before cardiac catheterization was incubated in vitro with therapeutic concentrations of unfractionated heparin (1.2 and 2.0 U/ml) alone and in combination with eptifibatide (unfractionated heparin 1.2 U/ml+eptifibatide, 1.7 microg/ml) or bivalirudin (8 and 14 microg/ml). An activated clotting time was determined. Platelet activation was induced with thrombin (0, 5, 15, and 40 U/ml) and assessed with the use of flow cytometry. Fibrin polymerization was prevented by the peptide Gly-Pro-Arg-Pro. The activation of glycoprotein IIb-IIIa and surface expression of P-selectin were identified with antibodies (PAC-1 and anti-CD62).

RESULTS

The activated clotting time was 258+/-13 s with 1.2 U/ml unfractionated heparin alone, 396+/-8 s with unfractionated heparin+eptifibatide, and 348+/-9 s with 8 microg/ml bivalirudin. The binding of PAC-1 (reflecting the potential to aggregate) was decreased most effectively by bivalirudin (percentage of platelets binding PAC-1 in response to 15 U/ml thrombin-unfractionated heparin=54+/-7%, unfractionated heparin+eptifibatide=12+/-4%, bivalirudin=1+/-0.3% of platelets, P<0.05 for bivalirudin compared with unfractionated heparin or unfractionated heparin+eptifibatide and unfractionated heparin+eptifibatide compared with unfractionated heparin). Bivalirudin prevented thrombin-induced surface expression of P-selectin more effectively than unfractionated heparin alone or unfractionated heparin+eptifibatide (percentage of platelets expressing P-selectin in response to 15 U/ml thrombin-unfractionated heparin alone=74+/-5%, unfractionated heparin+eptifibatide=53+/-7%, bivalirudin=1+/-0.3%, P<0.05 for bivalirudin compared with unfractionated heparin or unfractionated heparin+eptifibatide).

CONCLUSION

Comparison between pharmacologic concentrations shown to be therapeutic demonstrated that bivalirudin inhibited thrombin-induced activation of platelets to a greater extent than unfractionated heparin alone or in combination with eptifibatide.

Increased expression of platelet P-selectin and formation of platelet–leukocyte aggregates in blood from patients treated with unfractionated heparin plus eptifibatide compared with bivalirudin

INTRODUCTION

Platelet-leukocyte aggregates have been implicated in atherogenesis. This study was designed to determine the influence in vivo of a direct thrombin inhibitor, bivalirudin, compared with unfractionated heparin (UFH) plus the GP IIb-IIIa inhibitor eptifibatide (E) on platelet reactivity, the formation of platelet-leukocyte aggregates, and leukocyte activation.

MATERIALS AND METHODS

Blood was taken before and after percutaneous coronary intervention (PCI) from 60 patients randomized to UFH+E (n=26) or bivalirudin (n=34). Platelet function and the formation in vivo of platelet-monocyte aggregates (PMA) and platelet-neutrophil aggregates (PNA) were assessed with the use of flow cytometry. Myeloperoxidase (MPO) elaborated during leukocyte activation was measured by ELISA.

RESULTS

Compared with those treated with bivalirudin, patients treated with UFH+E exhibited a 45% decrease in the capacity of platelets to bind fibrinogen (p=0.006) but a 2-fold increase in platelet surface expression of P-selectin (p=0.04) in samples taken from the coronary ostium before PCI. Platelet-leukocyte aggregation in vivo was greater (PMA=2-fold, p=0.04; PNA=3-fold, p=0.006) with UFH+E as was the concentration in blood of MPO (1.5-fold, p=0.007).

CONCLUSIONS

Increased platelet surface expression of P-selectin, augmented platelet-leukocyte aggregation in vivo, and consequent activation of leukocytes was seen before PCI in blood from patients treated with UFH+E compared with bivalirudin. Benefits associated with decreased platelet aggregation when PCI is performed with UFH plus GP IIb-IIIa inhibition may be partially offset by increased platelet-leukocyte aggregation.

Matching the Evaluation of the Clinical Efficacy of Clopidogrel to Platelet Function Tests Relevant to the Biological Properties of the Drug

OBJECTIVES

This study aimed to explore platelet function tests relevant to the biological effects of clopidogrel that could help the clinical monitoring of drug efficacy.

BACKGROUND

Clopidogrel selectively inhibits the P2Y12 receptor, the major role of which is stabilization of aggregation, whereas initiation of aggregation depends on activity of both P2Y1 and P2Y12 receptors.

METHODS

Tests used were peak aggregation (Agg(max)) and late aggregation (Agg(6min)), and disaggregation, relating to P2Y1 and P2Y12 activity, respectively; and monoclonal antibody binding activated glycoprotein (GP) IIb/IIIa receptors (PAC-1) and P-selectin, measuring activation and secretion. A first study compared hirudin/PPACK (r-hirudin and D-phenylalanyl-prolyl-arginine chloromethyl ketone) with citrate as blood anticoagulant (16 patients), and a second control study compared the effects of clopidogrel, aspirin, or both (20 normal controls).

RESULTS

Clopidogrel similarly inhibited adenosine 5'-diphosphate (ADP)-induced Agg(max) with either anticoagulant, but significantly more Agg(6min) (75% vs. 31%), P-selectin (72% vs. 53%), and PAC-1 (62% vs. 24%) in hirudin/PPACK. In the control study, it inhibited Agg(max) by 22%, and Agg(6min), P-selectin, and PAC-1, by 69%, 66%, and 55%, respectively (all p < 0.05). Disaggregation at six min reached 62% with clopidogrel, but was virtually absent with placebo and aspirin. Non-responsiveness as evaluated by inhibition of Agg(max) in citrate was diagnosed in 35% of patients; in half this rate by Agg(6min), P-selectin, and PAC-1; and in 6% to 12% with the latter tests performed in hirudin/PPACK.

CONCLUSIONS

The evaluation of clopidogrel responsiveness by platelet function tests is largely influenced by the choice of blood preservative and functional tests. Measures of aggregation stabilization, and of consequent secretion and activation, identified most patients as responders, contrasting with measures of peak aggregation, by likely reflecting better the interactions clopidogrel and the P2Y12 receptor.

Tenecteplase and tirofiban in ST-segment elevation acute myocardial infarction: results of a randomized trial

BACKGROUND

The combination of older reduced-dose fibrinolytic agents and platelet glycoprotein IIb/IIIa inhibitors has shown modest improvements in reperfusion and more striking improvements in ST-segment resolution after acute myocardial infarction. We performed a multicenter dose-ranging study of reduced doses of a newer fibrinolytic (tenecteplase) combined with tirofiban, a glycoprotein IIb/IIIa inhibitor.

METHODS

The first goal of the trial was to identify a dose or doses of tirofiban that, when combined with reduced-dose tenecteplase, would result in a higher incidence of Thrombolysis In Myocardial Infarction (TIMI) grade 3 flow at 60 minutes versus full-dose tenecteplase alone. The second goal was to assess whether the optimum dose(s) from the first stage also would result in greater resolution of ST-segment elevation.

RESULTS

In all, 409 patients aged 18 to 75 years with myocardial infarction were enrolled. The incidence of TIMI grade 3 flow at 60 minutes did not differ significantly among dose groups, ranging from 50% to 68%. The corrected TIMI frame count likewise did not differ substantially (range 34-42). More patients given combined therapy had complete resolution of ST-segment elevation at 60 minutes compared with patients given tenecteplase alone. Major bleeding was infrequent, and no strokes occurred. Based on angiographic results of the first stage, the second planned stage of the study was not performed.

CONCLUSIONS

Although combination therapies were not associated with increased reperfusion compared with full-dose tenecteplase alone, similar TIMI flow grades were achieved despite reductions in tenecteplase doses. ST-segment resolution was more rapid and complete with combination therapy versus full-dose tenecteplase, suggesting enhanced microcirculatory perfusion to the infarct zone in this dose-ranging trial.

Hypotensive and toxicological study of citric acid and other constituents from Tagetes patula roots

Study of the effects of the methanolic extract of Tagetes patula roots on blood pressure led to the isolation of well known citric (1) and malic acid (7) as hypotensive, and pyridine hydrochloride (4) as hypertensive constituents of the plant along with a new constituent, 2-hydroxy, 5-hydroxymethyl furan (9). Citric acid and malic acid caused 71% and 43% fall in Mean Arterial Blood Pressure (MABP) of rats at the doses of 15 mg/kg and 30 mg/kg respectively while pyridine hydrochloride produced 34% rise in the MABP of rats at the dose of 30 mg/kg. LD50 and LD100 of citric acid in mice have been determined as 545 mg/kg and 1000 mg/kg, respectively.

Whole blood coagulation on protein adsorption-resistant PEG and peptide functionalised PEG-coated titanium surfaces

The aim of this study was to investigate whole blood coagulation on low blood plasma protein adsorbing surfaces. For this purpose, the polycationic graft copolymer poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG), PLL-g-PEG grafted with a cell adhesive peptide containing the amino acid sequence -Arg-Gly-Asp- (RGD), and PLL-g-PEG with a control peptide -Arg-Asp-Gly- (RDG) were adsorbed onto titanium (oxide), forming stable monomolecular adlayers through electrostatic attraction. Free oscillation rheometry and complementary techniques were used to measure the coagulation time (CT) and other interactions of the surfaces with native whole blood, recalcified platelet-rich plasma (PRP), and recalcified citrated platelet-free plasma (PFP). The results show that the uncoated titanium surfaces (reference) activated platelets and quickly triggered the coagulation cascade via the intrinsic pathway, whereas the PLL-g-PEG surfaces displayed a prolonged CT, approximately 2-3 times longer compared to uncoated titanium. We hypothesise that blood coagulates outside the vascular system independent of low protein adsorption to or activation by surfaces, due to the absence of an active down-regulation of procoagulative processes by the vascular endothelium.

Environmental influences on endovascular stent platelet reactivity: an in vitro comparison of stainless steel and gold surfaces

Thrombosis is an initiating reaction to vascular injury that follows the placement of vascular devices. Platelets play a crucial role in this response. Their interaction with endovascular devices is not solely a function of device properties, but a multifaceted response dependent on several biological factors that interact in the context of a hemodynamic environment. We sought to investigate the role of local environmental variations on determining indices of biocompatibility. Using a recently described in vitro flow apparatus, we separately studied the platelet and coagulative component responses to stainless steel endovascular stents with and without gold coating. When allowed to interact, these biological mediators of thrombosis enabled varied biocompatibility outcomes in a manner that was dependent on flow. Using platelet reactivity as an index, the stainless steel faired better under some conditions, while under other conditions, gold was superior. Considering such impacts of local environment on biocompatibility is important, both in the interpretation of experimental findings, as well as the continued use and optimized development of vascular devices.

Clinical measurement of thrombin generation by calibrated automated thrombography requires contact factor inhibition

BACKGROUND

Measurement of thrombin generation by calibrated automated thrombography (CAT) could fulfill the requirements of a global test of coagulability and is potentially applicable to routine clinical laboratory practice. The purpose of this study was to determine if corn trypsin inhibitor (CTI) could be used to abolish contact factor activation in this assay, thus allowing accurate measurement of low tissue factor (TF) concentration-triggered thrombin generation on samples taken in a routine clinical setting.

METHODS

The endogenous thrombin potential (ETP) was measured by CAT.

RESULTS

The study demonstrated that addition of CTI after plasma separation is not sufficient and blood must be drawn into tubes containing CTI if in-vitro contact factor-activated thrombin generation is to be abolished. Contact factor-activated thrombin generation is completely inhibited at a CTI concentration of 18.3 microg mL(-1) whole blood. Increasing the CTI concentration above this level does not lead to suppression of the TF-triggered ETP. At a TF concentration of 2 pmol, ETPs were significantly lower in the presence of CTI (P < 0.001). The difference (no CTI minus CTI) between results ranged from - 1 to 2159 nM min(-1) (median - 754). Whilst the low concentration TF-ETP assay was not optimized to distinguish degrees of coagulability between patient samples, there was a significant difference in ETP between normal and hemophilia samples and samples from patients with a clinical prothrombotic tendency.

CONCLUSIONS

CTI can be applied to ETP measurement by CAT. This permits the use of CAT in a low TF-triggered thrombin generation assay without concern for the effect of interference from in-vitro contact factor activation and the optimum reagent conditions for using CAT as a global test of coagulability in clinical practice can now be defined.