Current methods of measuring platelet activity: pros and cons

Direct real-time measurements of superoxide release from skeletal muscles in rat limbs and human blood platelets using an implantable Cytochrome C microbiosensor

Oxidative stress and excessive accumulation of the superoxide (O2.-) anion are at the genesis of many pathological conditions and the onset of several diseases. The real time monitoring of (O2.-) release is important to assess the extent of oxidative stress in these conditions. Herein, we present the design, fabrication and characterization of a robust (O2.-) biosensor using a simple and straightforward procedure involving deposition of a uniform layer of L-Cysteine on a gold wire electrode to which Cytochrome C (Cyt c) was conjugated. The immobilized layers, studied using conductive Atomic Force Microscopy (c-AFM) revealed a stable and uniformly distributed redox protein on the gold surface, visualized as conductivity and surface topographical plots. The biosensor enabled detection of (O2.-) at an applied potential of 0.15 V with a sensitivity of 42.4 nA/μM and a detection limit of 2.4 nM. Utility of the biosensor was demonstrated in measurements of real time (O2.-) release in activated human blood platelets and skeletal rat limb muscles following ischemia reperfusion injury (IRI), confirming the biosensor's stability and robustness for measurements in complex biological systems. The results demonstrate the ability of these biosensors to monitor real time release of (O2.-) and estimate the extent of oxidative injury in models that could easily be translated to human pathologies.

Platelet Function Testing: Update and Future Directions

Platelets play a key role in maintaining normal hemostasis and are also recognized as partners in the development of arterial thrombosis. Today, platelet function testing is used for very different clinical purposes; first, for investigation of platelet dysfunction in acute bleeding and diagnosis of platelet disorders in patients with long-lasting bleeding tendency, and second, for testing the efficacy of antiplatelet therapy in patients with increased thromboembolic risk. Moreover, it has been discussed whether platelet function testing can be used for prediction of bleeding risk (e.g., prior to major surgery). Ever since light transmission aggregometry was introduced, laboratories around the world have worked on testing platelet function, and during the last decades a wide range of new methods has emerged. Besides the clinical utility of platelet function testing, the present review summarizes the test principles and advantages and disadvantages of the different methods, depending on the purpose for which it is to be used. A critical step in investigation of platelet function is the preanalytical factors that can substantially affect test results. Therefore, this review also provides an overview of preanalytical variables that range from patient-related factors such as smoking, coffee, and exercise prior to blood sampling to selection of anticoagulant, needle gauge, and time from blood sampling to analyses. Finally, this review outlines further perspectives on platelet function testing for clinical practice and for research purposes.

Monitoring of Antiplatelet Therapy

In the late 1990s, the antithrombotic antiplatelet agent, clopidogrel, a P2Y12 inhibitor, was introduced. Around the same time, there was an increase in a number of new methods to measure platelet function (e.g., PFA-100 in 1995), and this has continued. It became evident that not all patients responded to clopidogrel in the same way and that some patients had a relative "resistance" to therapy, termed "high on-treatment platelet reactivity." This then led to some publications to advocate platelet function testing being used for patients on antiplatelet therapy. Platelet function testing was also suggested for use in patients awaiting cardiac surgery after stopping their antiplatelet therapy as a way of balancing thrombotic risk pre-surgery and bleeding risk perioperatively. This chapter will discuss some of the commonly used platelet function tests used in these settings, particularly those that are sometimes referred to as point-of-care tests or that require minimal laboratory sample manipulation. The latest guidance and recommendations for platelet function testing will be discussed following several clinical trials looking at the usefulness of platelet function testing in these clinical settings.

Challenges in Platelet Functions in HIV/AIDS Management

The interest in platelet functions in HIV/AIDS is due to the high incidence of microvascular thrombosis in these individuals. A lot of laboratory data have been generated regarding platelet functions in this population. The tests demonstrate platelet hyperactivity but decreased aggregation, though results are inconsistent depending on the study design. Antiretroviral treatments currently in use display complex interactions. Many studies on platelet functions in these patients have been for research purposes, but none have found utility in guiding drug treatment of thrombosis.

PLATELET FUNCTION IN TRAUMA: IS CURRENT TECHNOLOGY IN FUNCTION TESTING MISSING THE MARK IN INJURED PATIENTS?

ABSTRACT

Platelets are subcellular anucleate components of blood primarily responsible for initiating and maintaining hemostasis. After injury to a blood vessel, platelets can be activated via several pathways, resulting in changed shape, adherence to the injury site, aggregation to form a plug, degranulation to initiate activation in other nearby platelets, and acceleration of thrombin formation to convert fibrinogen to fibrin before contracting to strengthen the clot. Platelet function assays use agonists to induce and measure one or more of these processes to identify alterations in platelet function that increase the likelihood of bleeding or thrombotic events. In severe trauma, these assays have revealed that platelet dysfunction is strongly associated with poor clinical outcomes. However, to date, the mechanism(s) causing clinically significant platelet dysfunction remain poorly understood. We review the pros, cons, and evidence for use of many of the popular assays in trauma, discuss limitations of their use in this patient population, and present approaches that can be taken to develop improved functional assays capable of elucidating mechanisms of trauma-induced platelet dysfunction. Platelet dysfunction in trauma has been associated with need for transfusions and mortality; however, most of the current platelet function assays were not designed for evaluating trauma patients, and there are limited data regarding their use in this population. New or improved functional assays will help define the mechanisms by which platelet dysfunction occurs, as well as help optimize future treatment.