Preconditioning (PC) is the well-described phenomenon whereby brief episodes of myocardial ischemia render cardiomyocytes resistant to a later, sustained ischemic insult. However, evidence from our group has shown that PC has an ancillary, favorable effect on the maintenance of vessel patency in models of recurrent thrombosis mimicking clinical instances of acute ischemic syndromes. We hypothesized, in our previous application, that: (1) the enhanced patency seen with PC ischemia is due to a PC-induced attenuation in one or more molecular indices of platelet activation-aggregation;and (2) adenosine liberated during the PC stimulus, and resultant stimulation of adenosine A2A receptors on the platelets'surface, serves as the trigger for the improved patency. The first concept was supported by novel evidence of a significant, PC-induced down-regulation of platelet P-selectin expression, platelet-fibrinogen binding, and formation of neutrophil-platelet aggregates (NPAs). However, this favorable attenuation in molecular indices of platelet reactivity was not explained solely by platelet-A2A receptor stimulation. Accordingly, our aim in this competitive renewal is to expand on the platelet-A2A receptor paradigm and investigate the concept that the improved vessel patency initiated by PC ischemia is a consequence of a complex interplay among multiple triggers (i.e., adenosine and bradykinin) acting at multiple sites (receptors on neutrophils as well as platelets). We will use an an integrated analysis of physiologic and molecular-cellular endpoints, in multiple in vivo models of recurrent thrombosis (ranging from rats to genetically modified mice to dogs), to interrogate two primary hypotheses: (I) Neutrophils (i.e., formation of NPAs and activation of neutrophil L- selectin) contribute to the pathophysiology of recurrent thrombosis. Moreover, release of adenosine during PC ischemia contributes to the improved maintenance of vessel patency by an A2A-mediated down- regulation of neutrophil L-selectin activation. (II) Release of bradykinin during PC ischemia, and its rapid breakdown and production of stable bradykinin metabolites, contribute to the PC-induced augmentation of arterial patency via stimulation of platelet PAR4 receptors. Furthermore, we propose that the favorable effects of antecedent PC ischemia are not confined to a pretreatment strategy;rather: (III) 'PC'-based therapies, applied after the onset of recurrent thrombosis, improve arterial patency in our models of acute coronary syndromes. The ultimate goal of our proposal is to obtain novel mechanistic insights that may, in future, be exploited for the design of new treatments for patients at risk of developing thrombotic events.

Public Health Relevance

In patients with acute ischemic syndromes, failure to maintain coronary patency can precipitate multiple deleterious consequences, including prolonged hospitalization, an increased need for interventional procedures, and, most notably, a ~2-fold increase in mortality. Existing therapies aimed at reducing the probability of thrombotic events (most notably, prophylactic administration of aspirin and clopidogrel) are ineffective in an estimated 5-40% of patients. Thus, insights gained from the proposed experiments - i.e., identification of the mechanisms by which brief episodes of preconditioning ischemia and adenosine A2A receptor stimulation improve vessel patency - may, in future, be exploited in the design of novel anti-platelet strategies.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL072684-09
Application #
8296581
Study Section
Myocardial Ischemia and Metabolism Study Section (MIM)
Program Officer
Schwartz, Lisa
Project Start
2002-05-15
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2014-06-30
Support Year
9
Fiscal Year
2012
Total Cost
$338,580
Indirect Cost
$115,830
Name
Wayne State University
Department
Physiology
Type
Schools of Medicine
DUNS #
001962224
City
Detroit
State
MI
Country
United States
Zip Code
48202
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Whittaker, Peter; Przyklenk, Karin (2009) Fibrin architecture in clots: a quantitative polarized light microscopy analysis. Blood Cells Mol Dis 42:51-6
Linden, Matthew D; Barnard, Marc R; Frelinger, A L et al. (2008) Effect of adenosine A2 receptor stimulation on platelet activation-aggregation: differences between canine and human models. Thromb Res 121:689-98
Linden, M D; Whittaker, P; Frelinger 3rd, A L et al. (2006) Preconditioning ischemia attenuates molecular indices of platelet activation-aggregation. J Thromb Haemost 4:2670-7