Small aggregates of platelets can be detected sensitively by a flow cytometer equipped with an imaging device: mechanisms of epinephrine-induced aggregation and antiplatelet effects of beraprost

Convolutional neuronal network for identifying single-cell-platelet-platelet-aggregates in human whole blood using imaging flow cytometry

Imaging flow cytometry is an attractive method to investigate individual cells by optical properties. However, imaging flow cytometry applications with clinical relevance are scarce so far. Platelet aggregation naturally occurs during blood coagulation to form a clot. However, aberrant platelet aggregation is associated with cardiovascular disease under steady-state conditions in the blood. Several types of so-called antiplatelet drugs are frequently described to reduce the risk of stroke or cardiovascular diseases. However, an efficient monitoring method is missing to identify the presence and frequency of platelet-platelet aggregates in whole blood on a single cell level. In this work, we employed imaging flow cytometry to identify fluorescently labeled platelets in whole blood with a conditional gating strategy. Images were post-processed and aligned. A convolutional neural network was designed to identify platelet-platelet aggregates of two, three, and more than three platelets, and results were validated against various data set properties. In addition, the neural network excluded erythrocyte-platelet aggregates from the results. Based on the results, a parameter for detecting platelet-platelet aggregates, the weighted platelet aggregation, was developed. If employed on a broad scale with proband and patient samples, our method could aid in building a future diagnostic marker for cardiovascular disease and monitoring parameters to optimize drug prescriptions in such patient groups.

Intelligent Platelet Morphometry

Technological advances in image-based platelet analysis or platelet morphometry are critical for a better understanding of the structure and function of platelets in biological research as well as for the development of better clinical strategies in medical practice. Recently, the advent of high-throughput optical imaging and deep learning has boosted platelet morphometry to the next level by providing a new set of capabilities beyond what is achievable with traditional platelet morphometry, shedding light on the unexplored domain of platelet analysis. This Opinion article introduces emerging opportunities in 'intelligent' platelet morphometry, which are expected to pave the way for a new class of diagnostics, pharmacometrics, and therapeutics.

Precise Quantitative Analysis of Cell Targeting by Particle-Based Agents Using Imaging Flow Cytometry and Convolutional Neural Network

Understanding the intricacies of particle-cell interactions is essential for many applications such as imaging, phototherapy, and drug/gene delivery, because it is the key to accurate control of the particle properties for the improvement of their therapeutic and diagnostic efficiency. Recently, high-throughput methods have emerged for the detailed investigation of these interactions. For example, imaging flow cytometry (IFC) collects up to 60,000 images of cells per second (in 12 optical channels) and provides information about morphology and organelle localization in combination with fluorescence and side scatter intensity data. However, analysis of IFC data is extremely difficult to perform using conventional methods that calculate integral parameters or use mask-based object recognition. Here, we show application of a convolutional neural network (CNN) for precise quantitative analysis of particle targeting of cells using IFC data. CNN provides high-throughput object detection with almost human precision but avoids the subjective choice of image processing parameters that often leads to incorrect data interpretation. The method allows accurate counting of cell-bound particles with reliable discrimination from the nonbound particles in the field of view. The proposed method expands capabilities of spot counting applications (such as organelle counting, quantification of cell-cell and cell-bacteria interactions) and is going to be useful not only for high-throughput analysis of IFC data but also for other imaging techniques. © 2019 International Society for Advancement of Cytometry.

A microchip flow-chamber system for quantitative assessment of the platelet thrombus formation process

As the pathogenesis of arterial thrombosis often includes platelet thrombus formation (PTF), antiplatelet agents are commonly used for the prevention of thromboembolic events. Here, using a novel microchip flow-chamber system we developed to quantitatively analyze the PTF process, we evaluated the pharmacological efficacies of antiplatelet agents under different arterial shear rates. Hirudin-anticoagulated whole blood was perfused over a collagen-coated microchip at shear rates of 1000, 1500, and 2000s(-1), and PTF in the absence and presence of various antiplatelet agents was observed microscopically and quantified by measuring flow-pressure changes. The onset of PTF was measured as T(10) (time to reach 10 kPa), and AUC(10) (area under the flow pressure curve for the first 10 min) was calculated to quantify the overall stability of the formed thrombus. Aspirin and AR-C66096 (P2Y(12)-antagonist) at high concentrations (50 μM and 1000 nM, respectively) prolonged T(10) only modestly (AR-C66096>aspirin), but effectively decreased AUC(10), resulting in unstable PTF at all examined shear rates. With dual inhibition using both aspirin (25 μM) and ARC-66096 (250 nM), AUC(10) was drastically reduced. Nearly complete suppression of AUC(10) was also observed with abciximab (2 μg ml(-1)) and beraprost (PGI(2)-analog; 4 nM). Although OS-1 (GPIbα-antagonist; 100 nM) prevented complete capillary occlusion, significant amounts of microscopic thrombi were observed on the collagen surface. In contrast to abciximab and beraprost, OS-1 differentially affected PTF under higher shear conditions. Our novel analytical system is capable of distinguishing the pharmacological effects of various antiplatelet agents under physiological shear rates, suggesting that this system may aid in the determination of the appropriate type and dose of antiplatelet agent in the clinical setting.

Flow cytometric assessment of platelet aspirin resistance using light scattering

BACKGROUND

A simple and reliable assay is needed for the prediction of the clinical efficacy of antiplatelet aspirin therapy. We have devised another method for the evaluation of platelet function and aspirin resistance (AR), via conventional flow cytometry (FCM).

METHODS

To devise an optimized protocol for the assessment of platelet AR, various analytic variables of FCM were investigated. Using this devised protocol, AR was assessed in healthy subjects as an example.

RESULTS

The protocol utilized herein is as follows: citrate-anticoagulated platelet-rich plasma was mixed 1:1 with HEPES-buffered saline in two tubes, one of which is treated with aspirin. During the acquisition of FCM, arachidonate is added to the tube. The response of the aspirin-treated platelets is then compared with those of nontreated ones on a time/forward scatter plot. In the 61 total subjects, none was identified as aspirin resistant by this assay.

CONCLUSIONS

Using light scattering, platelet aggregation and aspirin's antiplatelet effects can be readily and cost-effectively detected. According to this assay, biochemical AR appears to be rare. This new protocol may prove useful in a clinical setting or as a research tool.

Past and Future Approaches to Assess the Quality of Platelets for Transfusion

No automated test exists to routinely measure platelet quality. Currently, the short, 5-day shelf life of platelet concentrates is largely dictated by the risk associated with bacterial contamination and not by platelet quality. With the implementation of bacterial testing and pathogen inactivation, platelet quality will become the major determinant for the shelf life of platelet concentrates. However, extended use of platelet concentrates stored beyond 5 days will require quality testing. In addition, high platelet quality would be expected to result in improved clinical efficacy, determined by count increment, improved hemostasis, and lower risk for adverse reactions in recipients. No in vitro quality test has yet demonstrated a good correlation with clinical efficacy or improved hemostasis. This review focuses on those tests of platelet quality that are based on platelet morphology. These include visual inspection of swirling, microscopic morphology score, measurement of light transmission through platelet concentrates, and platelet light scattering techniques. Recently, a new test for platelet quality has been introduced that uses dynamic light scattering. The advantages and remaining challenges for dynamic light scattering before it can become a routine platelet quality test are discussed.

Collagen-induced generation of platelet-derived microparticles in whole blood is dependent on ADP released from red blood cells and calcium ions

We have evaluated the effects of different anti-coagulants or agonists on the generation of platelet-derived microparticles (PMPs) using flow cytometry. Twenty microg/ml of collagen induced significantly greater PMP formation in whole blood anti-coagulated with argatroban, a selective thrombin inhibitor, as compared with platelet-rich plasma, or whole blood anti-coagulated with citrate. Thus, whole blood kept at the physiological Ca2+ concentration provides an optimal condition for the formation of PMP. Convulxin, a GPVI-selective agonist, also induced PMP formation at the magnitude which far exceeds those of other agonists, such as thrombin receptor-activating peptide, ADP or epinephrine. These findings suggest that GPVI-mediated platelet activation plays a key role in the formation of PMP in the presence of physiological Ca2+ in whole blood. The addition of red blood cells to PRP potentiated PMP formation induced by collagen. Pretreatment of whole blood with the combination of creatine phosphate and creatine phosphokinase reduced PMP formation induced by collagen. Blockade of ADP receptors, P2Y12 with AR-C69931MX and P2Y1 with A3P5P, respectively, further suppressed collagen-induced PMP formation. We conclude that ADP released from red blood cells enhances PMP formation induced by collagen, and that both P2Y12 and P2Y1 contribute to ADP-potentiation of PMP generation induced by collagen.