Transport Limitations of Nitric Oxide Inhibition of Platelet Aggregation under Flow

An "occlusive thrombosis-on-a-chip" microfluidic device for investigating the effect of anti-thrombotic drugs

Cardiovascular disease remains one of the world's leading causes of death. Myocardial infarction (heart attack) is triggered by occlusion of coronary arteries by platelet-rich thrombi (clots). The development of new anti-platelet drugs to prevent myocardial infarction continues to be an active area of research and is dependent on accurately modelling the process of clot formation. Occlusive thrombi can be generated in vivo in a range of species, but these models are limited by variability and lack of relevance to human disease. Although in vitro models using human blood can overcome species-specific differences and improve translatability, many models do not generate occlusive thrombi. In those models that do achieve occlusion, time to occlusion is difficult to measure in an unbiased and objective manner. In this study we developed a simple and robust approach to determine occlusion time of a novel in vitro microfluidic assay. This highlighted the potential for occlusion to occur in thrombosis microfluidic devices through off-site coagulation, obscuring the effect of anti-platelet drugs. We therefore designed a novel occlusive thrombosis-on-a-chip microfluidic device that reliably generates occlusive thrombi at arterial shear rates by quenching downstream coagulation. We further validated our device and methods by using the approved anti-platelet drug, eptifibatide, recording a significant difference in the "time to occlude" in treated devices compared to control conditions. These results demonstrate that this device can be used to monitor the effect of antithrombotic drugs on time to occlude, and, for the first time, delivers this essential data in an unbiased and objective manner.

The role of hyperbaric oxygen to platelet aggregation in noninsulin-dependent diabetes mellitus (NIDDM)

OBJECTIVES

Hyperglycemia in diabetes mellitus (DM) could cause rheological disorder, such as platelet aggregation and blood hyperviscosity. Hyperbaric oxygen (HBO) could decrease collagen as platelet aggregation agonist. This study aimed to explore the effect of HBO treatment to platelet aggregation parameters (latency time(LT), aggregation speed, aggregation index, and aggregation percentage) with the collagen aggregator in the noninsulin dependent diabetes mellitus (NIDDM).

METHODS

The number of subjects in this study were 16 for each group normoxia normobaric (NONB) and HBO. NIDDM patients from DM polyclinic in Rumah Sakit Angkatan Laut (RSAL) Dr Ramelan Surabaya which was fulfilled inclusion criteria would receive HBO Therapy. Control Group/NONB were treated with NONB condition (20% O₂ 1 ATA) for 90 min and treatment group/HBO were treated with hyperoxia hyperbaric condition (100% O₂ 2.4 ATA) for 3 × 30 min with interval of 2 × 5 min for inhaling fresh air. Subject has been blood taken for platelet aggregation test before and after HBO Therapy. The length of treatment was 5 days for both condition (NONB and HBO).

RESULTS

The data from both groups, NONB and HBO were tested first by normality test, homogenity test, correlation test, analysis of covariance, and paired t-test. Based on paired t-test, the decrease on platelet aggregation speed, aggregation index, and aggregation percentage after HBO treatment was showed significant difference on the LT and aggregation index while in aggregation speed and aggregation percentage was not significant. NONB group after 5 days was showed a significant difference on the aggregation speed and aggregation index while in LT and aggregation percentage was not significant.

CONCLUSIONS

The utilization of HBO 2.4 ATA 100% O₂ 3 × 30 min, once a day, for 5 days could decrease the platelet aggregation parameters (LT, aggregation speed, aggregation index, and aggregation percentage) in patients with NIDDM.

Targeting the Endothelium to Achieve Cardioprotection

Despite considerable improvements in the treatment of myocardial infarction, it is still a highly prevalent disease worldwide. Novel therapeutic strategies to limit infarct size are required to protect myocardial function and thus, avoid heart failure progression. Cardioprotection is a research topic with significant achievements in the context of basic science. However, translation of the beneficial effects of protective approaches from bench to bedside has proven difficult. Therefore, there is still an unmet need to study new avenues leading to protecting the myocardium against infarction. In line with this, the endothelium is an essential component of the cardiovascular system with multiple therapeutic targets with cardioprotective potential. Endothelial cells are the most abundant non-myocyte cell type in the heart and are key players in cardiovascular physiology and pathophysiology. These cells can regulate vascular tone, angiogenesis, hemostasis, and inflammation. Accordingly, endothelial dysfunction plays a fundamental role in cardiovascular diseases, which may ultimately lead to myocardial infarction. The endothelium is of paramount importance to protect the myocardium from ischemia/reperfusion injury via conditioning strategies or cardioprotective drugs. This review will provide updated information on the most promising therapeutic agents and protective approaches targeting endothelial cells in the context of myocardial infarction.

Functional Biodegradable Nitric Oxide Donor-Containing Polycarbonate-Based Micelles for Reduction-Triggered Drug Release and Overcoming Multidrug Resistance

Nitric oxide (NO), as a bioeffector to improve chemosensitivity by reversing multidrug resistance (MDR), is highly attractive for developing combinational delivery systems to deal with MDR tumors, while it is highly challenged by the stability and controlled release of NO during the pathway. Here we design and synthesize a cyclic nitrate trimethylene carbonate monomer (NTC), followed by ring-opening polymerization to prepare amphiphilic biodegradable polycarbonate-based copolymers as polymeric NO donors with tailored contents. The copolymer with desirable molecular weight is readily self-assembled to biodegradable micelles (NO-M) with a uniform size of 130 nm for highly stabilizing NO donors at the physiological conditions, while triggered NO release from micelles is performed at the intracellular reduction conditions. More importantly, NO-M shows superior inhibition of P-gP expression to enhance the chemosensitivity of multidrug-resistant MCF7 cells (MCF7/DOX^R). DOX-loaded NO-M (NO-M@DOX) realizes fast DOX release at the intracellular conditions, resulting in more intracellular DOX accumulation and higher antitumor activity mediated by the reduction-triggered NO/DOX release and NO-induced MDR reversal. Furthermore, the in vivo results show that NO-M@DOX effectively suppresses the MCF7/DOX^R tumor growth by a combination of directly NO-induced therapy and NO-mediated enhanced chemotherapy; meanwhile, the treatment with NO-M systems have much fewer side effects.

Flow chamber and microfluidic approaches for measuring thrombus formation in genetic bleeding disorders

Platelet adhesion and aggregation, coagulation, fibrin formation, and fibrinolysis are regulated by the forces and flows imposed by blood at the site of a vascular injury. Flow chambers designed to observe these events are an indispensable part of doing hemostasis and thrombosis research, especially with human blood. Microfluidic methods have provided the flexibility to design flow chambers with complex geometries and features that more closely mimic the anatomy and physiology of blood vessels. Additionally, microfluidic systems with integrated optics and/or pressure sensors and on-board signal processing could transform what have been primarily research tools into clinical assays. Here, we describe a historical review of how flow-based approaches have informed biophysical mechanisms in genetic bleeding disorders, challenges and potential solutions for developing models of bleeding in vitro, and outstanding issues that need to be addressed prior to their use in clinical settings.

Synthesis, antiplatelet and antithrombotic activities of resveratrol derivatives with NO-donor properties

Resveratrol (RVT) is a stilbene with a protective effect on the cardiovascular system; however, drawbacks including low bioavailability and fast metabolism limit its efficacy. In this work we described new resveratrol derivatives with nitric oxide (NO) release properties, ability to inhibit platelet aggregation and in vivo antithrombotic effect. Compounds (4a-f) were able to release NO in vitro, at levels ranging from 24.1% to 27.4%. All compounds (2a-f and 4a-f) have exhibited platelet aggregation inhibition using as agonists ADP, collagen and arachidonic acid. The most active compound (4f) showed reduced bleeding time compared to acetylsalicylic acid (ASA) and protected up to 80% against in vivo thromboembolic events. These findings suggest that hybrid resveratrol-furoxan (4f) is a novel lead compound able to prevent platelet aggregation and thromboembolic events.

Utility of microfluidic devices to study the platelet-endothelium interface

The integration of biomaterials and understanding of vascular biology has led to the development of perfusable endothelialized flow models, which have been used as valuable tools to study the platelet-endothelium interface under shear. In these models, the parameters of geometry, compliance, biorheology, and cellular complexity are varied to recapitulate the physical biology of platelet recruitment and activation under physiologically relevant conditions of blood flow. In this review, we summarize the mechanistic insights learned from perfusable microvessel models and discuss the potential utility as well as challenges of endothelialized microfluidic devices to study platelet function in the bloodstream in vitro.

Glycocalyx-Inspired Nitric Oxide-Releasing Surfaces Reduce Platelet Adhesion and Activation on Titanium

The endothelial glycocalyx lining the inside surfaces of blood vessels has multiple features that prevent inflammation, blood clot formation, and infection. This surface represents the highest standard in blood compatibility for long-term contact with blood under physiological flow rates. Engineering materials used in blood-contacting biomedical devices, including metals and polymers, have undesirable interactions with blood that lead to failure modes associated with inflammation, blood clotting, and infection. Platelet adhesion and activation are key events governing these undesirable interactions. In this work, we propose a new surface modification to titanium with three features inspired by the endothelial glcyocalyx: First, titanium surfaces are anodized to produce titania nanotubes with high surface area. Second, the nanostructured surfaces are coated with heparin-chitosan polyelectrolyte multilayers to provide glycosaminoglycan functionalization. Third, chitosan is modified with a nitric oxide-donor chemistry to provide an important antithrombotic small-molecule signal. We show that these surfaces are nontoxic with respect to platelets and leukocytes. The combination of glycocalyx-inspired features results in a dramatic reduction of platelet and leukocyte adhesion and platelet activation.

A vascular injury model using focal heat-induced activation of endothelial cells

Endothelial cells (EC) both inhibit and promote platelet function depending on their activation state. Quiescent EC inhibit platelet activation by constitutive secretion of platelet inhibitors. Activated EC promote platelet adhesion by secretion of von Willebrand factor (vWF). EC also secrete an extracellular matrix that support platelet adhesion when exposed following vascular injury. Previous studies of EC-platelet interactions under flow activate entire monolayers of cells by chemical activation. In this study, EC cultured in microfluidic channels were focally activated by heat from an underlying microelectrode. Based on finite element modeling, microelectrodes induced peak temperature increases of 10-40 °C above 37 °C after applying 5-9 V for 30 s resulting in three zones: (1) a quiescent zone corresponded to peak temperatures of less than 15 °C characterized by no EC activation or platelet accumulation. (2) An activation zone corresponding to an increase of 16-22 °C yielded EC that were viable, secreted elevated levels of vWF, and were P-selectin positive. Platelets accumulated in the retracted spaces between EC in the activation zone at a wall shear rate of 150 and 1500 s(-1). Experiments with blocking antibodies show that platelets adhere via GPIbα-vWF and α6β1-laminin interactions. (3) A kill zone corresponded to peak temperatures of greater than 23 °C where EC were not viable and did not support platelet adhesion. These data define heating conditions for the activation of EC, causing the secretion of vWF and the exposure of a subendothelial matrix that support platelet adhesion and aggregation. This model provides for spatially defined zones of EC activation that could be a useful tool for measuring the relative roles of anti- and prothrombotic roles of EC at the site of vascular injury.

Emerging microengineered tools for functional analysis and phenotyping of blood cells

The available techniques for assessing blood cell functions are limited considering the various types of blood cell and their diverse functions. In the past decade, rapid advances in microengineering have enabled an array of blood cell functional measurements that are difficult or impossible to achieve using conventional bulk platforms. Such miniaturized blood cell assay platforms also provide the attractive capabilities of reducing chemical consumption, cost, and assay time, as well as exciting opportunities for device integration, automation, and assay standardization. This review summarizes these contemporary microengineered tools and discusses their promising potential for constructing accurate in vitro models and rapid clinical diagnosis using minimal amounts of whole-blood samples.

Systems biology of platelet-vessel wall interactions

Platelets are small, anucleated cells that participate in primary hemostasis by forming a hemostatic plug at the site of a blood vessel's breach, preventing blood loss. However, hemostatic events can lead to excessive thrombosis, resulting in life-threatening strokes, emboli, or infarction. Development of multi-scale models coupling processes at several scales and running predictive model simulations on powerful computer clusters can help interdisciplinary groups of researchers to suggest and test new patient-specific treatment strategies.