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Microparticles in the serum: study of possible new biomarkers of plaque instability

Abstract

Atherosclerosis is a systemic inflammatory disease that can lead to myocardial infarction, stroke and ischemia. The microenvironment in an atherosclerotic plaque contains pro-inflammatory cytokines, high levels of oxidized low density lipoproteins (oxLDL) and reactive oxygen species (ROS). There is deposition of collagen that circumscribe the atheroma by the fibrous capsule, stabilizing its growth. Several lines of research have suggested that its instability and aggravation occur through stimuli of infectious agents. Studies in human atherosclerotic plaques demonstrate the presence of intense infection by microbial agents such as Mycoplasma pneumoniae (M.pneumoniae), where lipopolysaccharides and proteins would be released, stimulating the production of pro-inflammatory mediators. When exposed to stressful situations, these microorganisms are able to release microparticles (MPs, vesicles 100nm to 1¼m in diameter) containing proteins and genes in response to this stress, allowing their adaptation to various environments. Literature has been pointing MPs as having important role in endothelial dysfunction and free radical production. They participate in the intracellular communication and act in different pathological processes (including inflammatory response), being able to be biomarkers of acute events. We previously described exosomes (microvesicles smaller than 100nm) and MPs in atherosclerotic plaques and in the serum of atherosclerotic patients containing archea DNA, suggesting a possible infectious etiology for these MPs. Archaea are primitive microorganisms with oxidation capacity, which can contribute to inflammation, collagen fragmentation and plaque instability. Many papers describe archaeous genes in persistent pathogens, which could explain the large amount of M. pneumoniae inside the vulnerable plaques. Exosomes are described in cardiovascular diseases, acting as intercellular signaling organelles involved in several physiological and pathological processes.Recently we obtained very promising results by examining groups of 10 serum samples, as a subproject referring to the Brazilian Longitudinal Study of Adult Health (ELSA) and ERICO (Strategy of Registry of Accute Coronary Syndrome). For this first phase we received financial assistance from CNPq Universal Call (process 471854/2013), where the pellet and the supernatant of the sera of three groups were analyzed: atherosclerotic patients who had fatal AMI (died within one period of 30 days post-event), non-fatal AMI and stable atherosclerotic patients. In the serum of patients who evolved with fatal AMI, highernumber of MPs were found with archaeal DNA and M. pneumoniae, MMP9 and LDLox antigens. In the serum of patients who had non-fatal MI and those without infarction, significantly increasednumber of exosomes were found. The large amount of exosomes seems to play a role of oxidized lipoprotein removal and degradation of circulating blood collagenases, being plaque instability protectors.The main studiedbiomarkers focus on the quantification of inflammation; however, the immune response is non-specific and so far all these indicators have not been able to achieve sensitivity and specificity for clinical application. Imaging modalities have focused on the characteristics of vulnerable plaques, but it has become apparent that not all so-called vulnerable plaques lead to rupture and subsequent thrombosis, which limits their predictive value for patients at risk.In the present study we intend to increase the sample (N = 40 / group) using sera already stored in HU. Thus, to try to identify, in a quick and non-invasive manner, possible biomarkers of patients at risk for acute ischemic events, by performing flow cytometry (archaeal DNA), Western blot (LDLox, M. pneumoniae and MMP-9), zymography (MMP-9) and transmission electron microscopy for morphology confirmation. (AU)

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