Microfluidic assay of antiplatelet agents for inhibition of shear-induced platelet adhesion and activation

The rapid change of shear rate gradient is beneficial to platelet activation

Fluid shear plays a key role in hemostasis and thrombosis, and the purpose of this study was to investigate the effect of shear gradient change rate (SGCR) on platelet reactivity and von Willebrand factor (vWF) activity and its mechanism. In this study, we developed a set of microfluidic chips capable of generating different shear gradients and simulated the shear rate distribution in the flow field by COMSOL Multiphysics software. Molecular markers of platelet activation (P-selectin, activated GPIIb/IIIa, phosphatidylserine exposure, and monocyte-platelet aggregate formation) were analyzed by flow cytometry. Platelet aggregation induced by shear gradient was studied by a microfluidic experimental platform, and plasma vWF ristocetin cofactor (vWF: RCO) activity was investigated by flow cytometry. The expression of p-Akt was studied by Western blotting. The results showed that the faster the SGCR, the higher the expression of platelet p-Akt, and the stronger the platelet reactivity and vWF activity. This indicates that fluid shear stress can activate platelets and vWF in a shear gradient-dependent manner through the PI3K/AKT signal pathway, and the faster the SGCR, the more significant the activation effect.

Recent advances in microfluidic technology of arterial thrombosis investigations

Microfluidic technology has emerged as a powerful tool in studying arterial thrombosis, allowing researchers to construct artificial blood vessels and replicate the hemodynamics of blood flow. This technology has led to significant advancements in understanding thrombosis and platelet adhesion and aggregation. Microfluidic models have various types and functions, and by studying the fabrication methods and working principles of microfluidic chips, applicable methods can be selected according to specific needs. The rapid development of microfluidic integrated system and modular microfluidic system makes arterial thrombosis research more diversified and automated, but its standardization still needs to be solved urgently. One key advantage of microfluidic technology is the ability to precisely control fluid flow in microchannels and to analyze platelet behavior under different shear forces and flow rates. This allows researchers to study the physiological and pathological processes of blood flow, shedding light on the underlying mechanisms of arterial thrombosis. In conclusion, microfluidic technology has revolutionized the study of arterial thrombosis by enabling the construction of artificial blood vessels and accurately reproducing hemodynamics. In the future, microfluidics will place greater emphasis on versatility and automation, holding great promise for advancing antithrombotic therapeutic and prophylactic measures.

Investigation of the role of von Willebrand factor in shear-induced platelet activation and functional alteration under high non-physiological shear stress

BACKGROUND

von Willebrand factor (vWF) plays a crucial role in physiological hemostasis through platelet and subendothelial collagen adhesion. However, its role in shear-induced platelet activation and functional alteration under non-physiological conditions common to blood-contacting medical devices (BCMDs) is not well investigated.

METHODS

Fresh healthy human blood was treated with an anti-vWF antibody to block vWF-GPIbα interaction. Untreated blood was used as a control. They were exposed to three levels of non-physiological shear stress (NPSS) (75, 125, and 175 Pa) through a shearing device with an exposure time of 0.5 s to mimic typical shear conditions in BCMDs. Flow cytometric assays were used to measure the expression levels of PAC-1 and P-Selectin and platelet aggregates for platelet activation and the expression levels of GPIbα, GPIIb/IIIa, and GPVI for receptor shedding. Collagen/ristocetin-induced platelet aggregation capacity was characterized by aggregometry.

RESULTS

The levels of platelet activation and aggregates increased with increasing NPSS in the untreated blood. More receptors were lost with increasing NPSS, resulting in a decreased capacity of collagen/ristocetin-induced platelet aggregation. In contrast, the increase in platelet activation and aggregates after exposure to NPSS, even at the highest level of NPSS, was significantly lower in treated blood. Nevertheless, there was no notable difference in receptor shedding, especially for GPIIb/IIIa and GPVI, between the two blood groups at the same level of NPSS. The block of vWF exacerbated the decreased capacity of collagen/ristocetin-induced platelet aggregation.

CONCLUSIONS

High NPSS activates platelets mainly by enhancing the vWF-GPIbα interaction. Platelet activation and receptor shedding induced by high NPSS likely occur through different pathways.

Impact of rise and fall phases of shear on platelet activation and aggregation using microfluidics

Blood flow disorders are often the result of the non-physiological narrowing of blood arteries caused by atherosclerosis and thrombus. The blood then proceeds through rising-peak-decreasing phases as it passes through the narrow area. Although abnormally high shear is known to activate platelets, the shear process that platelets undergo in small arteries is complex. Thus, understanding how each shear phase affects platelet activation can be used to improve antiplatelet therapy and decrease the risk of side effects like bleeding. Blood samples were sheared (68.8 ms,5200 s-1) in vitro by the microfluidic technique, and platelet activation levels (P-selectin and integrin αIIbβ3) and von Willebrand factor (vWF) binding to platelets were analyzed by flow cytometry. Post-stenosis platelet aggregation was dynamically detected using microfluidic technology. We studied TXA2, P2Y12-ADP, and integrin αIIbβ3-fibrinogen receptor pathways by adding antiplatelet drugs, such as acetylsalicylic acid (ASA, an active ingredient of aspirin that inhibits platelet metabolism), ticagrelor (hinders platelet activation), and tirofiban (blocks integrin αIIbβ3 receptor) in vitro, respectively, to determine platelet activation function mediated by transient non-physiological high shear rates. We demonstrated that platelets can be activated under transient pathological high shear rates. The shear rise and fall phases influenced shear-induced platelet activation by regulating the binding of vWF to platelets. The degree of platelet activation and aggregation increased with multiple shear rise and fall phases. ASA did not inhibit shear-mediated platelet activation, but ticagrelor and tirofiban effectively inhibited shear-mediated platelet activation. Our data demonstrated that the shear rise and fall phases play an important role in shear-mediated platelet activation and promote platelet activation and aggregation in a vWF-dependent manner. Blocking integrin αIIbβ3 receptor and hindering P2Y12-ADP were beneficial to reducing shear-mediated platelet activation.

Antiplatelet Agents Inhibit Platelet Adhesion and Aggregation on Glass Surface Under Physiological Flow Conditions: Toward a Microfluidic Platelet Functional Assay Without Additional Adhesion Protein Modification

ABSTRACT

As the pathogenesis of arterial thrombosis often includes platelet adhesion and aggregation, antiplatelet agents are commonly used to prevent thromboembolic events. Here, a new microfluidic method without additional adhesion protein modification was developed to quantify the inhibitory effect of antiplatelet drugs on the adhesion and aggregation behavior of platelets on glass surfaces under physiological flow conditions. Polydimethylsiloxane-glass microfluidic chips were fabricated by soft photolithography. Blood samples from healthy volunteers or patients before and after taking antiplatelet drugs flowed through the microchannels at wall shear rates of 300 and 1500 second -1 , respectively. The time to reach 2.5% platelet aggregation surface coverage (Ti), surface coverage (A 150s ), and mean fluorescence intensity (F 150s ) were used as quantitative indicators. Aspirin (80 μM) prolonged Ti and reduced F 150s . Alprostadil, ticagrelor, eptifibatide, and tirofiban prolonged Ti and reduced A 150s and F 150s in a concentration-dependent manner, whereas high concentrations of alprostadil did not completely inhibit platelet aggregation. Aspirin combined with ticagrelor synergistically inhibited platelet adhesion and aggregation; GPIb-IX-von Willebrand factor inhibitors partially inhibited platelet aggregation, and the inhibition was more pronounced at 1500 than at 300 second -1 . Patient administration of aspirin or (and) clopidogrel inhibited platelet adhesion and aggregation on the glass surface under flow conditions. This technology is capable of distinguishing the pharmacological effects of various antiplatelet drugs on inhibition of platelet adhesion aggregation on glass surface under physiological flow conditions, which providing a new way to develop microfluidic platelet function detection method without additional adhesive protein modification for determining the inhibitory effects of antiplatelet drugs in the clinical setting.

Insights in the Prothrombotic Changes After Implantation of a Left Ventricular Assist Device in Patients With End-Stage Heart Failure: A Longitudinal Observational Study

Thrombus formation is a common complication during left ventricular assist device (LVAD) therapy, despite anticoagulation with vitamin K antagonists (VKA) and a platelet inhibitor. Plasma levels of markers for primary and secondary hemostasis and contact activation were determined before LVAD implantation and 6 and 12 months thereafter in 37 adults with end-stage heart failure. Twelve patients received a HeartMate 3, 7 patients received a HeartWare, and 18 patients received a HeartMate II. At baseline, patients had elevated plasma levels of the platelet protein upon activation, β-thromboglobulin, and active von Willebrand factor in thrombogenic state (VWFa), which remained high after LVAD implantation. Von Willebrand factor levels and VWF activity were elevated at baseline but normalized 12 months after LVAD implantation. High D -dimer plasma levels, at baseline, remained elevated after 12 months. This was associated with an increase in plasma thrombin-antithrombin-complex levels and plasma levels of contact activation marker-cleaved H-kininogen after LVAD implantation. Considering these results it could be concluded that LVAD patients show significant coagulation activation despite antithrombotic therapy, which could explain why patients are at high risk for LVAD-induced thrombosis. Continuous low-grade systemic platelet activation and contact activation may contribute to prothrombotic effects of LVAD.

Studying the efficacy of antiplatelet drugs on atherosclerosis by optofluidic imaging on a chip

Vascular stenosis caused by atherosclerosis instigates activation and aggregation of platelets, eventually resulting in thrombus formation. Although antiplatelet drugs are commonly used to inhibit platelet activation and aggregation, they unfortunately cannot prevent recurrent thrombotic events in patients with atherosclerosis. This is partially due to the limited understanding of the efficacy of antiplatelet drugs in the complex hemodynamic environment of vascular stenosis. Conventional methods for evaluating the efficacy of antiplatelet drugs under stenosis either fail to simulate the hemodynamic environment of vascular stenosis characterized by high shear stress and recirculatory flow or lack spatial resolution in their analytical techniques to statistically identify and characterize platelet aggregates. Here we propose and experimentally demonstrate a method comprising an in vitro 3D stenosis microfluidic chip and an optical time-stretch quantitative phase imaging system for studying the efficacy of antiplatelet drugs under stenosis. Our method simulates the atherogenic flow environment of vascular stenosis while enabling high-resolution and statistical analysis of platelet aggregates. Using our method, we distinguished the efficacy of three antiplatelet drugs, acetylsalicylic acid (ASA), cangrelor, and eptifibatide, for inhibiting platelet aggregation induced by stenosis. Specifically, ASA failed to inhibit stenosis-induced platelet aggregation, while eptifibatide and cangrelor showed high and moderate efficacy, respectively. Furthermore, we demonstrated that the drugs tested also differed in their efficacy for inhibiting platelet aggregation synergistically induced by stenosis and agonists (e.g., adenosine diphosphate, and collagen). Taken together, our method is an effective tool for investigating the efficacy of antiplatelet drugs under vascular stenosis, which could assist the development of optimal pharmacologic strategies for patients with atherosclerosis.

Application of microfluidic chip technology to study the inhibitory effect of tetramethylpyrazine on platelet aggregation, activation, and phosphatidylserine exposure mediated by pathological high shear rate

OBJECTIVE

In order to study the antithrombotic effect and mechanism of tetramethylpyrazine (TMA).

METHODS

In this study, we developed a microfluidic chip model that can mimic normal arteries and stenotic arterial vessels, and studied the inhibitory effects of TMA on platelet aggregation, activation (P-selectin, GPIIb/IIIa, monocyte-platelet aggregates) and phosphatidyl serine (PS) exposure. In addition, we also investigated the effect of TMA on ADP and ristocetin-induced platelet aggregation by turbidimetry.

RESULTS

The results showed that TMA significantly inhibited the platelet aggregation, activation and PS exposure induced by pathological high shear rate. Under static conditions, TMA can inhibit ADP and ristocetin-induced platelet aggregation.

CONCLUSION

The results indicated that TMA mainly inhibited platelet aggregation, activation and PS exposure by inhibiting the binding of von Willebrand factor (vWF) to the GPIb/IX/V complex, and partially inhibited platelet aggregation through the platelet P2Y 12 -ADP receptor pathway.

Patient specific approach to analysis of shear-induced platelet activation in haemodialysis arteriovenous fistula

Shear-induced platelet activation (SIPAct) is an important mechanism of thrombosis initiation under high blood flow. This mechanism relies on the interaction of platelets with the von Willebrand factor (VWF) capable of unfolding under high shear stress. High shear stress occurs in the arteriovenous fistula (AVF) commonly used for haemodialysis. A novel patient-specific approach for the modelling of SIPAct in the AVF was proposed. This enabled us to estimate the SIPAct level via computational fluid dynamics. The suggested approach was applied for the SIPAct analysis in AVF geometries reconstructed from medical images. The approach facilitates the determination of the SIPAct level dependence on both biomechanical (AVF flow rate) and biochemical factors (VWF multimer size). It was found that the dependence of the SIPAct level on the AVF flow rate can be approximated by a power law. The critical flow rate was a decreasing function of the VWF multimer size. Moreover, the critical AVF flow rate highly depended on patient-specific factors, e.g., the vessel geometry. This indicates that the approach may be adopted to elucidate patient-specific thrombosis risk factors in haemodialysis patients.

Fully automated light transmission aggregometry on a disc for platelet function tests

Platelet function tests, a group of assays that measure the ability of platelets to aggregate and promote clotting in a sample of blood, are performed in various medical fields to assess inherited platelet function disorders and monitor antiplatelet therapies. Light transmission aggregometry (LTA) is considered the gold standard for platelet function assessment. However, the lack of a standardized protocol is a major drawback when applied at the point of care. Moreover, it is a time-consuming and labor-intensive assay that requires a large volume of blood. Here, we describe the design, fabrication, and operation of a centrifugal microfluidic disc that can perform a fully automated LTA assay from a small volume of a whole blood sample (<1 mL), achieving highly reproducible results (3.2% coefficient of variation) within a short period (<25 min). The assays performed with this device yield more precise and accurate results than traditional LTA because of the automation of the reaction steps, minimal human operation, robust detection strategy via the distinctive structure of the microfluidic chamber, and quick analysis that minimizes the adverse effects of platelet instability.

Shear Stress Accumulation Enhances von Willebrand Factor-Induced Platelet P-Selectin Translocation in a PI3K/Akt Pathway-Dependent Manner

Platelet adhesion and activation through the interaction of von Willebrand factor (VWF) with platelet glycoprotein (GP) Ibα are the early key events in hemostasis and thrombosis especially under high blood shear stress. P-selectin translocation from α granule to the cell surface is a typical platelet function phenotype, which makes the platelet-induced inflammatory response of flowing leukocytes possible and can be induced by either chemical agonists (thrombin, ADP, etc.) or high blood shear stress, but regulations of VWF mutation and blood shear stress on VWF-induced P-selectin translocation remain unclear. With flow cytometry, parallel plate flow chamber, and immunofluorescence staining techniques, we examined the P-selectin translocation of platelets on immobilized wild-type (WT) VWF-A1 domain and its two mutants, the gain-of-function (GOF) mutant R1308L and the loss-of-function (LOF) mutant G1324S, respectively. The results showed that the VWF-A1-induced platelet P-selectin translocation was triggered, accelerated, and enhanced by fluid shear stress and could be correlated with shear stress accumulation (SSA, the product of fluid shear stress and mechanical stimulus time), and the PI3K/Akt axis was involved in the platelet P-selectin translocation. The force-triggered P-selectin translocation occurred quickly on partial platelet surface first and then extended gradually to the whole platelet surface as SSA increased. The P-selectin translocation process would be promoted by the GOF mutation (R1308L) but slowed down by the LOF mutation (G1324S). These findings demonstrated a force-enhanced regulation mechanism for the VWF-induced platelet P-selectin translocation through the PI3K/Akt pathway and provided a novel insight into the mechano-chemical regulation mechanism for the key events, such as platelet activation and functional phenotype change in hemostasis and thrombosis.

Assessment of therapeutic platelet inhibition in cardiac patients: Comparative study between VerifyNow-P2Y12 and Anysis-P2Y12 assay

BACKGROUND

Analyzing responsiveness to P2Y12 therapy is vital to preventing thrombotic and hemorrhagic complications in patients with cardiovascular diseases.

OBJECTIVE

This study evaluates a new Anysis-P2Y12 assay system against VerifyNow-P2Y12 in cardiac patients and analyzes the P2Y12 low-response rates of the two devices with various cutoff values.

METHODS

In total, 125 citrated blood samples were collected from cardiac patients referred for a P2Y12 antiplatelet response test. In the Anysis assay, the test result was the migration distance (MD) until the blood flow stops, which is comparable to both P2Y12 reaction units and percent inhibition obtained using VerifyNow.

RESULTS

The MDs without and with P2Y12 were 182±30 and 264±12 mm, respectively (p <  0.0001). Compared to VerifyNow-P2Y12, the sensitivity and specificity of Anysis-200 were 96.8%and 88.7%, respectively. Cohen's kappa coefficient between the two devices was 0.761, indicating a high agreement. However, there was an apparent difference in the low-response rate to P2Y12, which was 36.5%for VerifyNow and 5.9%for Anysis.

CONCLUSIONS

The performance of the newly developed platelet function assay, Anysis-P2Y12 was equivalent to that of VerifyNow-P2Y12 in terms of sensitivity and specificity. The Anysis-P2Y12 assay may help screen patients with abnormal P2Y12 non-responsiveness.