Biomarkers of Atherosclerosis A study of plasma and solid tissues from animal and human models using nuclear magnetic resonance (NMR) technology

Introduction: Current recommendations for surgical management of asymptomatic 50-99% carotid stenosis are guided by two factors, patient’s fitness for surgical intervention and the clinical/imaging features associated with an increased risk of late stroke. Despite the advances in imaging modalities and their ability to detect some features of plaque instability, full understanding the pathophysiology of plaque instability will allow early intervention in patients with high risk of developing stroke from the unstable plaque. To date, no serum or urine marker has been shown to predict plaque instability and the risk of future cerebrovascular events. Aims and methods: The aim of this study was to compare metabolic profiles of plasma and plaques from patients with symptomatic carotid stenosis undergoing endarterectomy, plasma and plaques from patients with symptomatic femoral stenosis, and plasma from patients without carotid or femoral disease (control). We also aim to compare plasma and solid tissues from mammalian model (mice), and further compare them to the human experiment. Nuclear magnetic resonance (NMR) spectroscopy will be used to analyse the metabolic profiles of plasma and plaques, and potentially identify predictive biomarkers of plaque instability. Animal experiment was carried out using 6 apolipoprotein E–deficient versus 6 control mice. For the human experiment, carotid and femoral plaques alongside plasma and urine samples were collected from 84 patients. NMR analysis was performed on all the samples and further analysis was done on the resulting spectra and correlating data. Results: The animal experiment showed weak models with inconclusive outcomes. Plasma human experiment also showed weak models and could not confidently establish certain metabolites as atherosclerotic biomarkers. However, similarities were observed between the animal and human models, and 3 metabolites (2-oxoglutarate, choline and taurine) were identified as potential biomarkers. In contrary, human solid tissue experiments have shown much stronger models and clearer results. Spectra gained from these experiments were the first to be described, with no comparable studies in the literature. The most notable finding is the possible effect of taurine on carotid plaques. Taurine signals have been observed in the animal (plasma and solid) as well as human plasma models in this study. Although, they were merely affecting the control groups. Conclusions: Identifying plaque instability in asymptomatic carotid disease was the centre of this study. Taurine’s strong influence on the metabolic profiling of carotid plaques raises the possibility of a potential biomarker of plaque instability. Further work is required regarding the histological examination of plaque sections. An objective assessment of the plaque instability will improve the study outcome and add a different aspect to the current results.