STUDIES ON THE MECHANISMS INVOLVED IN THE PATHOGENESIS OF COCAINE-ASSOCIATED BRAIN PERFUSION DEFECTS: THE ROLE OF ENDOTHELIAL DYSFUNCTION AND ACTIVATION OF HEMOSTATIC SYSTEM
Cocaine consumption is a major problem worldwide being probably the most frequent cause of drug related deaths. In Chile, about 1.0 % of the population between 12 and 64 years are regular users of cocaine or free base (SENDA, 2010 Annual Report on Drug Situation in Chile), which constitutes one of the highest rates of consumption in the world according to the World Drug Report from United Nations. Cocaine use is a well-established risk factor for life-threatening vascular ischemic disease, affecting both, the cardiovascular and the cerebrovascular territories. Clinically, cocaine abusers have an increased risk for myocardial infarction, angina pectoris, cardiac sudden death, ischemic stroke and cerebral circulation abnormalities (regional brain perfusion defects, rBPD). The pathogenesis of these vascular complications is not fully understood and several mechanisms have been proposed, including 1) vasoconstriction 2) increased oxygen consumption and 3) atherothrombosis. Although cocaine may cause vasospasm, this effect is insufficient to explain the complex and long lasting ischemic events observed in these patients. In this sense, it has been proposed for a long time that accelerated atherosclerosis and secondary thrombosis may play an important role in the pathogenesis of cocaine-induced vascular abnormalities. In this line, we demonstrated in cocaine users evidence of systemic platelet activation (Pereira et al., Platelets 2011; 22: 596) and endothelial dysfunction (ED) (Saez et al., Thromb Res 2011; 128:18), two key phenomena that contribute to atherothrombosis. Moreover, we observed that all chronic cocaine users have rBPD which were associated with markers of ED and significant neurocognitive impairment (Massardo et al. J Nucl Med 2012; 53(S1):2017). Studying the pathogenesis of cocaine-associated ED, we have preliminarily found Rho kinase activation (ROCK) in circulating leukocytes of cocaine users, in the aorta of rats treated with cocaine and in Human Umbilical Vein Endothelial Cells (HUVEC) exposed to the drug. These data suggest that ROCK activation -a central pathway in vascular remodelling and damageis critical in the pathogenesis cocaine-associated vascular injury. Considering our observations that the main vascular impact of cocaine is on the cerebral circulation, our findings raised key questions to be addressed: the effect of cocaine on brain endothelial cells (bEC); whether cocaine induces ROCK activation in the brain and its contribution to blood flow disturbances in vivo and the role of platelet/ hemostatic system activation in generating a prothrombotic microenvironment in cerebral circulation. Our working hypothesis is that cocaine-associated activation of RhoA/Rho kinase in brain microvascular endothelial cells induces proinflammatory and prothrombotic changes which are key players in the pathogenesis of regional cerebral blood flow abnormalities. Our general goal is to determine whether activation of RhoA/Rho kinase pathway caused by cocaine or its metabolites in brain endothelial cells, contributes to the pathogenesis of brain perfusion abnormalities; specifically, by the induction of an inflammatory phenotype, endothelial barrier disruption, platelet and leukocyte adhesion/ and local fibrin deposit with generation of a prothrombotic milieu in the cerebral microvasculature. Our specific goals are: 1) in vitro studies to determine the molecular mechanisms and the consequences of cocaine-induced activation of ROCK in brain microvascular endothelial cells (HBMVEC) and 2) in vivo studies to demonstrate that RhoA/Rho kinase pathway activation contributes to the development of brain perfusion abnormalities associated with cocaine use. To accomplish these goals we propose to use 1) A brain endothelial cell model in vitro to determine signaling pathways involved in cocaine-mediated ROCK activation; nitric oxide availability and generation of reactive oxygen species. We will study changes in bEC permeability and the role of platelet/bEC interaction in cell permeability and leukocyte transmigration. We will determine the generation of a bEC prothrombotic phenotype upon exposure to cocaine. Moreover, we will characterize cocaine-mediated platelet/bEC interaction under flow conditions. 2) Using a novel functional magnetic resonance imaging technique (fMRI) in living animals, we will study whether cocaine administration in rats induces systemic endothelial dysfunction and its relevance in brain-blood barrier disruption and disturbances in cerebral blood flow. Finally, using fMRI we will explore in the rat model, whether cocaine promotes intravascular fibrin deposit in brain circulation. This proposal will address several questions raised by data generated in our previous studies. Specifically we expect to provide important insights into the molecular and cellular mechanisms involved in cocaineassociated brain circulation derangement, since it seems to be one of the most constant and significant medical adverse effects of cocaine use. Its association with neurocognitive impairment –a determinant of relapse- highlights the importance of exploring new therapeutic windows to dampen cocaine-induce vascular damage based in a better understanding of its pathophysiology.
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