Evidence of Platelet Activation at Medically Used Hypothermia and Mechanistic Data Indicating ADP as a Key Mediator and Therapeutic Target

Abstract

Objective-Hypothermia is used in various clinical settings to inhibit ischemia-related organ damage. However, prothrombotic effects have been described as potential side effects. This study aimed to elucidate the mechanism of hypothermia-induced platelet activation and subsequent prothrombotic events and to develop preventative pharmacological strategies applicable during clinically used hypothermia. Methods and Results-Platelet function was investigated ex vivo and in vivo at clinically used hypothermia (28°C/18°C).Hypothermic mice demonstrated increased expression of platelet activation marker P-selectin, platelet-leukocyte aggregate formation, and thrombocytopenia. Intravital microscopy of FeCl 3 -injured murine mesenteric arteries revealed increased platelet thrombus formation with hypothermia. Ex vivo flow chamber experiments indicated increased platelet-fibrinogen adhesion under hypothermia. We show that hypothermia results in reduced ADP hydrolysis via reduction of CD39 (E-NTPDase1) activity, resulting in increased levels of ADP and subsequent augmented primary and secondary platelet activation. In vivo administration of ADP receptor P 2 Y 12 antagonists and recombinant soluble CD39 prevented hypothermia-induced thrombus formation and thrombocytopenia, respectively. Key Words: platelet receptor blockers Ⅲ platelets Ⅲ ADP Ⅲ CD39 Ⅲ hypothermia C ooling as a means of reducing oxygen requirements of organs was initially reported in 1950 by Bigelow et al 1 This concept was first implemented in cardiac surgery in 1952, when John Lewis and his team used total-body hypothermia for the closure of an atrial septal defect. 2 Since then, hypothermia has been routinely used in cardiac surgery as an adjunct to extracorporeal circulation (ECC) with the aim of protecting organs against ischemia-related damage. Temperatures applied are usually between 28°C and 32°C. Furthermore, during deep hypothermic circulatory arrest (which is used either in congenital cardiac surgery, for operations on the thoracic aorta in adults, or in neurosurgical operations for the treatment of cerebral aneurysms), temperatures lower than 20°C are used. Mild hypothermia is also used successfully in emergency and intensive care medicine to improve survival and neurological outcomes of patients after cardiac arrest. [3][4][5][6] Potential prothrombotic events of medically used hypothermia are of major concern. In fact, increased activation, aggregation, and sequestration of platelets and (micro)vascular thrombus formation have all been seen in both in vitro and in vivo settings at hypothermia. 4,[7][8][9][10][11][12][13][14][15][16][17] An increased platelet response to activation at temperatures less than 37°C could be considered part of human physiology. It has been proposed that platelets act as thermosensors, being less responsive to thrombogenic stimuli at the core body temperature of the central circulation, where coronary or cerebral thrombus formation could be lethal. However, at the lower temperatures of external body surfaces, the sites ...

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Are there sufficient standards for the in vitro hemocompatibility testing of biomaterials?

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Development of a novel strategy to target CD39 antithrombotic activity to the endothelial-platelet microenvironment in kidney ischemia–reperfusion injury

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