Circulating cell-derived microparticles – potential markers of cardiovascular risk
Circulating cell-derived microparticles, released from cells during activation and apoptosis, are involved in inflammation, coagulation and endothelial dysfunction, all important processes in the development of cardiovascular disease. This project aimed to adapt and validate a flow cytometric assay to measure microparticles derived from various cell types, and to utilise this assay for the investigation of microparticles in healthy individuals and patients with cardiovascular-associated diseases. A lack of standardisation of pre-analytical variables has impeded the study of microparticles. Pre-analytical variables were analysed, and small changes in methodology were found to have a large impact on microparticle levels detected. Functional microparticle assays were also investigated, and results from these assays were found to be significantly associated with the quantitative results from the flow cytometry assay. Healthy individuals were recruited to establish a normal range. Interestingly, in healthy individuals, hypoxia induced by exposure to moderate altitude, was shown to cause a decrease in procoagulant, platelet-derived and red blood cell-derived microparticles. Obstructive sleep apnoea is a common syndrome, associated with an increased risk of cardiovascular disease. Microparticle levels were determined in two randomised controlled trials, investigating the impact of therapy in these patients. Initiation of treatment for six months in minimally symptomatic patients led to a decrease in procoagulant microparticles. Withdrawal of treatment for two weeks in moderate/severe patients led to an increase in endothelial-derived, granulocyte-derived and monocyte-derived microparticles. Finally circulating microparticles were investigated in patients with cardiovascular-associated conditions. Patients undergoing a dobutamine stress echocardiogram (DSE), for the identification of coronary artery disease, were studied. Patients with a negative DSE exhibited an increase in procoagulant, platelet-derived, endothelial-derived and red blood cell-derived microparticles during stress testing, which was not evident in patients with a positive DSE, suggesting that microparticles provide additional diagnostic value in this setting. In the rapidly developing field of microparticle analysis, the flow cytometric assay described in this thesis, is reproducible, flexible and correlates well with functional microparticle assays. It has also been shown to provide novel and potentially clinically relevant results in a variety of clinical conditions associated with cardiovascular disease.
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