| 1. |
- Boknäs, Niklas, et al.
(författare)
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Flow cytometry-based platelet function testing is predictive of symptom burden in a cohort of bleeders
- 2018
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Ingår i: Platelets. - : Taylor & Francis. - 0953-7104 .- 1369-1635. ; 29:5, s. 512-519
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Tidskriftsartikel (refereegranskat)abstract
- Platelet function disorders (PFDs) are common in patients with mild bleeding disorders (MBDs), yet the significance of laboratory findings suggestive of a PFD remain unclear due to the lack of evidence for a clinical correlation between the test results and the patient phenotype. Herein, we present the results from a study evaluating the potential utility of platelet function testing using whole-blood flow cytometry in a cohort of 105 patients undergoing investigation for MBD. Subjects were evaluated with a test panel comprising two different activation markers (fibrinogen binding and P-selectin exposure) and four physiologically relevant platelet agonists (ADP, PAR1-AP, PAR4-AP, and CRP-XL). Abnormal test results were identified by comparison with reference ranges constructed from 24 healthy controls or with the fifth percentile of the entire patient cohort. We found that the abnormal test results are predictive of bleeding symptom severity, and that the greatest predictive strength was achieved using a subset of the panel, comparing measurements of fibrinogen binding after activation with all four agonists with the fifth percentile of the patient cohort (p = 0.00008, hazard ratio 8.7; 95% CI 2.5-40). Our results suggest that whole-blood flow cytometry-based platelet function testing could become a feasible alternative for the investigation of MBDs. We also show that platelet function testing using whole-blood flow cytometry could provide a clinically relevant quantitative assessment of platelet-related hemostasis.
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| 2. |
- Boknäs, Niklas, 1979-, et al.
(författare)
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Platelet function testing at low platelet counts : When can you trust your analysis?
- 2019
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Ingår i: Research and Practice in Thrombosis and Haemostasis. - : Wiley-Blackwell. - 2475-0379. ; 3:2, s. 285-290
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Tidskriftsartikel (refereegranskat)abstract
- Background: Although flow cytometry is often brought forward as a preferable method in the setting of thrombocytopenia, the relative effects of low sample counts on results from flow cytometry-based platelet function testing (FC-PFT) in comparison with light transmission aggregometry (LTA) and multiple electrode aggregometry (MEA) has not been reported.Objectives: To compare the effects of different sample platelet counts (10, 50, 100, and 200x10(9)L(-1)) on platelet activation measured with FC-PFT, LTA, and MEA using the same anticoagulant and agonist concentrations as for the commercial MEA test.Methods: Platelets were stimulated with two commonly used platelet agonists (ADP [6.5 mu molL(-1)] and PAR1-AP [TRAP, 32 mu molL(-1)]). The specified sample platelet counts were obtained by combining platelet-rich and platelet poor hirudinized plasma in different proportions with or without red blood cells.Results: For FC, P-selectin exposure and PAC-1 binding was reduced at 10x10(9)L(-1) after stimulation with PAR1-AP (by approximately 20% and 50%, respectively), but remained relatively unchanged when ADP was used as agonist (n=9). The platelet count-dependent effects observed with PAR1-AP were eliminated when samples were pre-incubated with apyrase, implying that reduced purinergic signaling was the main underlying factor (n=5). Both aggregometry-based PFTs showed a 50% reduction at 50x10(9)L(-1) and more than 80% reduction at 10x10(9)L(-1), irrespective of agonist used (n=7).Conclusions: Although FC-PFT is generally preferable to aggregometry-based PFTs in situations with low sample platelet counts, a careful optimization of experimental parameters is still required in order to eliminate platelet count-related effects.
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| 3. |
- Connolly-Andersen, Anne-Marie, et al.
(författare)
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Increased Thrombopoiesis and Platelet Activation in Hantavirus-Infected Patients
- 2015
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Ingår i: Journal of Infectious Diseases. - : Oxford University Press. - 0022-1899 .- 1537-6613. ; 212:7, s. 1061-1069
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Tidskriftsartikel (refereegranskat)abstract
- Background. Thrombocytopenia is a common finding during viral hemorrhagic fever, which includes hemorrhagic fever with renal syndrome (HFRS). The 2 main causes for thrombocytopenia are impaired thrombopoiesis and/or increased peripheral destruction of platelets. In addition, there is an increased intravascular coagulation risk during HFRS, which could be due to platelet activation. Methods. Thrombopoiesis was determined by quantification of platelet counts, thrombopoietin, immature platelet fraction, and mean platelet volume during HFRS. The in vivo platelet activation was determined by quantification of soluble P-selectin (sP-selectin) and glycoprotein VI (sGPVI). The function of circulating platelets was determined by ex vivo stimulation followed by flow cytometry analysis of platelet surface-bound fibrinogen and P-selectin exposure. Intravascular coagulation during disease was determined by scoring for disseminated intravascular coagulation (DIC) and recording thromboembolic complications. Results. The levels of thrombopoietin, immature platelet fraction, and mean platelet volume all indicate increased thrombopoiesis during HFRS. Circulating platelets had reduced ex vivo function during disease compared to follow-up. Most interestingly, we observed significantly increased in vivo platelet activation in HFRS patients with intravascular coagulation (DIC and thromboembolic complications) as shown by sP-selectin and sGPVI levels. Conclusions. HFRS patients have increased thrombopoiesis and platelet activation, which contributes to intravascular coagulation.
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| 4. |
- Deb, S., et al.
(författare)
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Individual variation in hemostatic alterations caused by tyrosine kinase inhibitors : a way to improve personalized cancer therapy?
- 2016
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Ingår i: Thrombosis Research. - : Elsevier. - 0049-3848 .- 1879-2472. ; 140:Suppl. 1, s. S196-S197
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: During the last two decades, Bcr-Abl tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of chronic myelogenous leukemia (CML), and are now considered standard treatment for this disease. However, TKIs can induce serious hemostatic side effects including cardiovascular disease and bleeding disorders. Blood platelet aggregation and formation of pro-coagulant platelets are important to allow a well-balanced hemostatic response. Therefore, a detailed understanding of what effect different TKIs exert on platelets and hemostasis could help to understand if there are differences of importance to minimize the risk of bleeding complications in treated patients.AIM: To investigate how TKIs used in CML (imatinib, dasatinib, nilotinib, bosutinib, and ponatinib) affect platelet activation and hemostasis.MATERIALS AND METHODS: We have developed a multi-parameter six color flow cytometry protocol to study different aspects of platelet function upon activation, e.g. formation of aggregatory (PAC-1-positive) and pro-coagulant (phosphatidylserine-exposing) platelets, exocytosis of alpha- and lysosomal granules and mitochondrial membrane potential.This protocol was performed in presence or absence of TKIs in blood from normal donors and in treated patients. Whole blood aggregometry (Multiplate®), thrombin generation in platelet-rich plasma and in vitro thrombus formation by free oscillation rheometry (ReoRox G2) was further evaluated in some situations.RESULTS: At clinically relevant concentrations, dasatinib significantly decreased the formation of procoagulant platelets. Ponatinib induced a slight decrease in formation of procoagulant platelets, whereas bosutinib and nilotinib showed opposite tendencies (n=7). Dasatinib also decreased platelet aggregation (n=4-6) and in vitro thrombus formation (n=3). Thrombin generation was not significantly affected by therapeutic levels of TKIs, whereas higher doses of dasatinib, bosutinib, ponatinib and imatinib significantly changed one or several of the thrombin generation parameters (n=7-8). Interestingly, large differences in response to the drugs were observed among the healthy donors, especially for dasatinib and bosutinib. Major inter-individual variations were also observed in dasatinib-treated patients, see Figure 1.CONCLUSIONS: Different TKIs show varying potency to affect platelet-based hemostasis. In addition, we found large inter-individual variations in how some drugs affected platelet function. Therefore, we suggest that development of a clinically useful protocol for platelet function testing could help to identify patients more susceptible to adverse drug reactions. Such a protocol could potentially help clinicians to gain insight into the risk of side effects, which could help to choose the most suitable drug for each individual patient.
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| 5. |
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| 6. |
- Lindahl, Tomas, et al.
(författare)
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Caveats in studies of the physiological role of polyphosphates in coagulation
- 2016
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Ingår i: Biochemical Society Transactions. - : Portland Press. - 0300-5127 .- 1470-8752. ; 44:1, s. 35-39
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Tidskriftsartikel (refereegranskat)abstract
- Platelet-derived polyphosphates (polyP), stored in dense granule and released upon platelet activation, have been claimed to enhance thrombin activation of coagulation factor XI (FXI) and to activate FXII directly. The latter claim is controversial and principal results leading to these conclusions are probably influenced by methodological problems. It is important to consider that low-grade contact activation is initiated by all surfaces and is greatly amplified by the presence of phospholipids simulating the procoagulant membranes of activated platelets. Thus, proper use of inhibitors of the contact pathway and a careful choice of materials for plates and tubes is important to avoid artefacts. The use of phosphatases used to degrade polyP has an important drawback as it also degrades the secondary activators ADP and ATP, which are released from activated platelets. In addition, the use of positively charged inhibitors, such as polymyxin B, to inhibit polyP in platelet-rich plasma and blood is problematic, as polymyxin B also slows coagulation in the absence of polyP. In conclusion we hope awareness of the above caveats may improve research on the physiological roles of polyP in coagulation.
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| 7. |
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| 8. |
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| 9. |
- Macwan, Ankit, et al.
(författare)
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Gradient-dependent inhibition of stimulatory signaling from platelet G protein-coupled receptors
- 2019
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Ingår i: Haematologica. - : Ferrata Storti Foundation. - 0390-6078 .- 1592-8721. ; 104:7
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Tidskriftsartikel (refereegranskat)abstract
- As platelet activation is an irreversible and potentially harmful event, platelet stimulatory signaling must be tightly regulated to ensure the filtering-out of inconsequential fluctuations of agonist concentrations in the vascular milieu. Herein, we show that platelet activation via G protein-coupled receptors is gradient-dependent that is determined not only by agonist concentrations per se but also by how rapidly concentrations change over time. We demonstrate that gradient-dependent inhibition is a common feature of all major platelet stimulatory G protein-coupled receptors, while platelet activation via the non- G protein-coupled receptor glycoprotein VI is strictly concentration-dependent. By systematically characterizing the effects of variations in temporal agonist concentration gradients on different aspects of platelet activation, we demonstrate that gradient-dependent inhibition of protease-activated receptors exhibit different kinetics, with platelet activation occurring at lower agonist gradients for protease-activated receptor 4 than for protease-activated receptor 1, but share a characteristic bimodal effect distribution, as gradient-dependent inhibition increases over a narrow range of gradients, below which aggregation and granule secretion is effectively shut off. In contrast, the effects of gradient-dependent inhibition on platelet activation via adenosine diphosphate and thromboxane receptors increase incrementally over a large range of gradients. Further, depending on the affected activation pathway, gradient-dependent inhibition results in different degrees of refractoriness to subsequent autologous agonist stimulation. Mechanistically, our study identifies an important role for the cyclic adenosine monophosphate-dependent pathway in gradient-dependent inhibition. Together, our findings suggest that gradient-dependent inhibition may represent a new general mechanism for hemostatic regulation in platelets.
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