Imaging of structural changes in endothelial cells and thrombus formation at the site of FeCl(3)-induced injuries in mice cremasteric arteries

Acute pulmonary hypertension due to microthrombus formation following COVID-19 vaccination: a case report

BACKGROUND

Several side effects have been reported after mRNA COVID-19 vaccinations. Nonetheless, the risk of pulmonary hypertension (PH) is rarely reported. Most cases with acute PH following vaccination were due to macropulmonary embolism secondary to deep vein thrombosis. However, acute PH due to microthrombus formation after COVID-19 vaccination has not been reported before, although a microthrombus has been considered to lead to the dysfunction of multiple organs, particularly in patients infected with COVID-19.

CASE SUMMARY

A 63-year-old woman without any past medical history presented to our hospital with facial and bilateral pedal oedema and progressive dyspnoea on exertion. Her symptoms began the day after her second COVID-19 vaccination and developed gradually, which prompted her to seek consultation in our hospital 6 weeks later. An echocardiogram revealed substantially elevated right heart pressure, and cardiac catheterization revealed high pulmonary artery pressure (mean PAP, 30 mmHg). Contrast-enhanced computed tomography and venous echography revealed no apparent thrombus, and ventilation/perfusion (V/Q) scintigraphy revealed no V/Q mismatch. However, elevated D-dimer indicated the presence of a coagulation-fibrinolysis system in her body; thus, heparin therapy was initiated intravenously on Day 3 for 4 days, followed by direct oral anticoagulants ended on Day 16. Her symptoms substantially improved as her D-dimer level decreased, and a follow-up cardiac catheterization on Day 14 revealed a decline in mean PAP (15 mmHg).

DISCUSSION

Our case suggests that the presence of acute PH is likely due to microangiopathy. Further studies are required to reveal the relationship between immune responses and microthrombus formation after COVID-19 vaccination.

Multi-Scale Imaging of Vascular Pathologies in Cardiovascular Disease

Cardiovascular disease entails systemic changes in the vasculature. The endothelial cells lining the blood vessels are crucial in the pathogenesis of cardiovascular disease. Healthy endothelial cells direct the blood flow to tissues as vasodilators and act as the systemic interface between the blood and tissues, supplying nutrients for vital organs, and regulating the smooth traffic of leukocytes into tissues. In cardiovascular diseases, when inflammation is sensed, endothelial cells adjust to the local or systemic inflammatory state. As the inflamed vasculature adjusts, changes in the endothelial cells lead to endothelial dysfunction, altered blood flow and permeability, expression of adhesion molecules, vessel wall inflammation, thrombosis, angiogenic processes, and extracellular matrix production at the endothelial cell level. Preclinical multi-scale imaging of these endothelial changes using optical, acoustic, nuclear, MRI, and multimodal techniques has progressed, due to technical advances and enhanced biological understanding on the interaction between immune and endothelial cells. While this review highlights biological processes that are related to changes in the cardiac vasculature during cardiovascular diseases, it also summarizes state-of-the-art vascular imaging techniques. The advantages and disadvantages of the different imaging techniques are highlighted, as well as their principles, methodologies, and preclinical and clinical applications with potential future directions. These multi-scale approaches of vascular imaging carry great potential to further expand our understanding of basic vascular biology, to enable early diagnosis of vascular changes and to provide sensitive diagnostic imaging techniques in the management of cardiovascular disease.

Safety of antithrombotic therapy in East Asian patients

Antithrombotic agents are widely used on the globe for prevention of thrombotic events such as atherothrombotic events and thromboembolic stroke in atrial fibrillation or for prevention and treatment of venous thromboembolism. However, the net clinical benefit of antithrombotic intervention may differ substantially in various sub-population of patients. Here, the authors attempt to address the risk of serious bleeding in East Asian as compared to the other regions of the world. The community-based epidemiological data suggest numerically higher risk of hemorrhage stroke in East Asian as compared to the globe. Importantly, the life-time risk of ischemic stroke in East Asia is higher than that of the globe. Regarding the serious bleeding risk in East Asians with the use of antithrombotic agents, various clinical trials and international registries provided conflicting information. It is hard to draw generalized conclusion, but there are some specific sub-population in East Asian with higher risk of specific serious bleeding events with the use of specific antithrombotic agents such as the risk of intra-cranial bleeding (ICH) with Vitamin K antagonists. Specific characteristics in East Asian such as higher prevalence of lacunar stroke may contribute higher risk of ICH in East Asian, but the detailed mechanism is still to be elucidated. In conclusion, further investigations are necessary to clarify the specific conditions where the risk of serious bleeding events in East Asian patients differ substantially compared to the global. In addition, further understanding of the mechanisms causing the different bleeding response in specific conditions in East Asian is awaited.

New approaches for the assessment of platelet activation status in thrombus under flow condition using confocal microscopy

The goal of the study was the assessment of heterogeneous platelet activation status in thrombus. In a ferric(III) chloride (FeCl₃) thrombosis (intravital) model of C57BL/6 J mice, the area of irreversibly activated (phosphatidylserine (PS)-positive) platelets was assessed after 1-s exposure of a vessel to FeCl₃. In a laser-induced thrombosis (intravital) model of GFP mice, the area of the thrombus composed of PS-negative platelets was evaluated. The ratio of the area of PECAM-1 to the area of the thrombus was used as a marker to assess the activity of PS-negative platelets. In the in vitro flow chamber model, the thrombus area (PS-negative and PS-positive platelets) and the platelet activation index (ratio of the area of PS-positive platelets to the area of thrombus) were determined. To assess platelet activation status with these models, acetylsalicylic acid (ASA) and iloprost (Ilo) were used. In the FeCl₃ thrombosis, ASA (10 mg/kg, 100 mg/kg) decreased the area of PS-positive platelets. In the laser thrombosis, ASA (10 mg/kg) decreased the thrombus area, but the decrease in platelet activity was evident even at 3 mg/kg by an increased PECAM-1/thrombus ratio. In the flow chamber, ASA (0.02 mg/ml, 0.2 mg/ml) equally decreased the platelet activation index, whereas only at 0.2 mg/ml, it decreased the thrombus area. Ilo (3.6 ng/ml, 36 ng/ml) decreased the thrombus area but at 36 ng/ml increased the platelet activation index. We showed that intravital models and flow chamber provide a detailed assessment of platelet activation status and the mechanism of drug action.

Evaluation of commonly used tests to measure the effect of single-dose aspirin on mouse hemostasis

Discrepancies in preclinical studies of aspirin (ASA) antiplatelet activity in mouse models of bleeding and arterial thrombosis led us to evaluate commonly reported methods in order to propose a procedure for reliably measuring the effects of single dose ASA on mouse hemostasis. FVB and C57Bl6 mice received 100 mg/kg of ASA or vehicle orally 30 min or 3 h prior to investigate either hemostasis using the tail bleeding assay or carotid thrombosis induced by FeCl₃, or to blood sampling for isolated platelet aggregation and TXB₂ generation. Expected inhibition of COX1 by ASA was ascertained by a strong decrease in TXB₂ production, and its effect on platelet function and hemostasis, by decreased collagen-induced aggregation and increased bleeding time, respectively. Strikingly, we determined that anti-hemostatic effects of ASA were more predictable 30 min after administration than 3 h later. Conversely, ASA did not alter time to arterial occlusion of the carotid upon FeCl₃-induced thrombosis, suggesting ASA not to be used as reference inhibitor drug in this model of arterial thrombosis.

Potential different impact of inhibition of thrombin function and thrombin generation rate for the growth of thrombi formed at site of endothelial injury under blood flow condition

INTRODUCTION

Thrombin inhibitor and anti-Xa are now widely used in clinical practice. However, the difference between thrombin inhibitor and anti-Xa in prevention of thrombosis is still to be elucidated.

MATERIALS AND METHODS

Computer simulator implementing the function of platelet, coagulation, fibrinolysis and blood flow was developed. The function of thrombin is defined as to activated platelet at the rate of 0.01 s^-1 and to produce fibrin at the rate of 0.1 s^-1 in control. The effect of thrombin inhibitor was settled to reduce the rate of platelet activation and fibrin generation changed from 10 to 100% as compared to the control. The local thrombin generation rate on activated platelet was settled as 1.0 s^-1 as a control. The effect of anti-Xa was settled to reduce to thrombin generation rate on activated platelet from 10% to 100% as compared to the control. The sizes of thrombi formed at site of endothelial injury in the presence and absence of thrombin inhibitor and anti-Xa were compared.

RESULTS AND CONCLUSIONS

The size of thrombi formed by 30-s perfusion of blood at site of endothelial injury reduced both in the presence of thrombin inhibitor and anti-Xa. There was significant positive relationship between thrombin inhibitor effect and the size of formed thrombi with R value of 0.96. (p < 0.0001) However, the sizes of thrombi were not influence by anti-Xa until it decreased 30% or less as compared to control. There was no significant relationship between anti-Xa effect and the size of formed thrombi. (R = 0.39, p = 0.09) Our results suggest the different dose-dependent effects of thrombin inhibitor and anti-Xa on thrombus formation at least in specific conditions. Computer simulation may help to predict quantitative antithrombotic effects of various antithrombotic agents.

Platelet receptors as therapeutic targets: Past, present and future

Anti-platelet drugs reduce arterial thrombosis after plaque rupture and erosion, prevent stent thrombosis and are used to prevent and treat myocardial infarction and ischaemic stroke. Some of them may also be helpful in treating less frequent diseases such as thrombotic thrombocytopenic purpura. The present concise review aims to cover current and future developments of anti-platelet drugs interfering with the interaction of von Willebrand factor (VWF) with glycoprotein (GP) Ibα, and directed against GPVI, GPIIb/IIIa (integrin αIIbβ3), the thrombin receptor PAR-1, and the ADP receptor P2Y12. The high expectations of having novel antiplatelet drugs which selectively inhibit arterial thrombosis without interfering with normal haemostasis could possibly be met in the near future.

Prediction of Molecular Interaction between Platelet Glycoprotein Ibα and von Willebrand Factor using Molecular Dynamics Simulations

AIM

The molecular mechanism of the unique interaction between platelet membrane glycoprotein Ibα (GPIbα) and von Willebrand Factor (VWF), necessary for platelet adhesion under high shear stress, is yet to be clarified.

METHODS

The molecular dynamics simulation using NAMD (Nanoscale Molecular Dynamics) package with the CHARMM 22 (Chemistry at Harvard Macromolecular Mechanics) force field were used to predict dynamic structural changes occurring in the binding site of A1 domain of VWF and N terminus domain of GPIbα under water soluble condition.

RESULTS

The mean distance between the mass center of A1 domain of VWF and GPIbα in the stable form was predicted as 27.3 Å. The potential of mean force between the A1 domain of VWF and GPIbα were calculated in conditions of various distances of the mass center between them. All the calculated values were fitted to the Morse potential energy function curve. The maximum adhesive force between A1 domain of VWF and GPIbα was predicted as 62.3 pN by differentiating the potential of mean force with respect to the molecular distance.

CONCLUSIONS

The molecular dynamics simulation is useful for predicting the dynamic structure changes of protein bonds involved in platelet adhesion and for predicting the adhesive forces generated between their interactions.

Development of virtual platelets implementing the functions of three platelet membrane proteins with different adhesive characteristics

AIM

Computer simulation is a new method for understanding biological phenomena. In this report, we developed a simple platelet simulator representing platelet adhesion under blood flow conditions.

METHODS

We generated virtual platelets based on the functions of three key adhesive proteins: glycoprotein (GP) Ibα, GPIIb/IIIa and collagen receptors. The adhesive force between GPIbα and von Willebrand factor (VWF) was set to increase in association with increments in the fluid shear stress. GPIIb/IIIa acquires an adhesive force to bind with ligands only when platelets are activated following multiple GPIbα stimulation by VWF or collagen receptors.

RESULTS

Upon perfusion over the area of virtual endothelial injury, the virtual platelets adhered and became activated to form platelet thrombi. A total of 286/mm(2) of activated platelets was found to have accumulated downstream of the flow obstacle within 30 seconds, with 59/mm(2) platelets adhering upstream. The results obtained with the virtual model were consistent with those for real platelets in human blood in the presence of similarly shaped flow obstacles.

CONCLUSIONS

Our computer platelet simulator, which employs the functions of three key platelet membrane proteins, shows similar findings for adhesion in the presence and absence of blood flow obstacles.

Imaging fibrin formation and platelet and endothelial cell activation in vivo

Over the past six decades research employing in vitro assays has identified enzymes, cofactors, cell receptors and associated ligands important to the haemostatic process and its regulation. These studies have greatly advanced our understanding of the molecular and cellular bases of haemostasis and thrombosis. However, in vitro assays cannot simultaneously reproduce the interactions of all of the components of the haemostatic process that occur in vivo nor do they reflect the importance of haemodynamic factors resulting from blood flow. To overcome these limitations investigators have increasingly turned to animal models of haemostasis and thrombosis. In this article we describe some advances in the visualisation of platelet and endothelial cell activation and blood coagulation in vivo and review what we have learned from our intravital microscopy experiments using primarily the laser-induced injury model for thrombosis.

Permanent occlusion of feeding arteries and draining veins in solid mouse tumors by vascular targeted photodynamic therapy (VTP) with Tookad

Background

Antiangiogenic and anti-vascular therapies present intriguing alternatives to cancer therapy. However, despite promising preclinical results and significant delays in tumor progression, none have demonstrated long-term curative features to date. Here, we show that a single treatment session of Tookad-based vascular targeted photodynamic therapy (VTP) promotes permanent arrest of tumor blood supply by rapid occlusion of the tumor feeding arteries (FA) and draining veins (DV), leading to tumor necrosis and eradication within 24–48 h.

Methodology/Principal Findings

A mouse earlobe MADB106 tumor model was subjected to Tookad-VTP and monitored by three complementary, non-invasive online imaging techniques: Fluorescent intravital microscopy, Dynamic Light Scattering Imaging and photosensitized MRI. Tookad-VTP led to prompt tumor FA vasodilatation (a mean volume increase of 70%) with a transient increase (60%) in blood-flow rate. Rapid vasoconstriction, simultaneous blood clotting, vessel permeabilization and a sharp decline in the flow rates then followed, culminating in FA occlusion at 63.2 sec±1.5SEM. This blockage was deemed irreversible after 10 minutes of VTP treatment. A decrease in DV blood flow was demonstrated, with a slight lag from FA response, accompanied by frequent changes in flow direction before reaching a complete standstill. In contrast, neighboring, healthy tissue vessels of similar sizes remained intact and functional after Tookad-VTP.

Conclusion/Significance

Tookad-VTP selectively targets the tumor feeding and draining vessels. To the best of our knowledge, this is the first mono-therapeutic modality that primarily aims at the larger tumor vessels and leads to high cure rates, both in the preclinical and clinical arenas.