EVALUATION OF BIOMARKERS OF ENDOTHELIN-1 SYNTHESIS AS DIAGNOSTIC TOOLS FOR CORONARY HEART DISEASE AND HEART FAILURE

Over the past ten years there has been a marked reduction in the number of deaths from heart disease. A major factor contributing to this is the wider use of a group of medicines called statins. Large clinical trials including the Heart Protection Study played a key role in demonstrating the important protective actions of statins for patients with symptoms of heart disease, as well as for those who are likely to develop disease because of high cholesterol levels or other risk factors. However, this study was unable to predict those who had the most active disease and likely to suffer from heart attacks or other vascular events such as stroke. If a simple diagnostic test became available to detect people at highest risk of disease at an early stage, this would allow more intensive medical treatment, as well as diet and lifestyle advice to cut their risk of life-threatening vascular events or sudden death.

Endothelin is a vasoconstrictor peptide produced by the endothelium (a single layer of cells that line every blood vessel). Research over the past twenty years has strongly implicated endothelin in the underlying processes leading to heart disease. But measuring endothelin in blood samples is too difficult to provide a reliable means of diagnosis. However, when endothelin is produced in cells it is synthesized as part of a large protein called proendothelin. Because fragments of this protein are also secreted with endothelin it is likely that one of these fragments can provide a reliable indicator of the level of endothelin production, and indirectly the presence of active heart disease.

The aims of this project are: (1) to identify the best fragment of proendothelin to use as a new diagnostic test, and (2) to evaluate the usefulness of this test to detect people with heart disease. The diagnostic potential of this new test will be evaluated in a two-step process. Firstly, samples from a well-characterised set of 500 diabetic patients who have undergone detailed screening for heart disease, and progression of disease will be used to assess which is the best method of proendothelin measurement for identifying active heart disease. The second stage of validation will be to apply the best method to measurement of the baseline samples from the 20,536 subjects participating in the Heart Protection Study. These investigations are likely to lead to a new diagnostic test for screening for heart disease.

Early diagnosis of coronary heart disease (CHD), and identification of people at risk of developing disease at a point where medical, dietary and lifestyle strategies can play a bigger role in prevention remains one of the biggest healthcare challenges. Over the past fifteen years endothelial dysfunction has been recognised as a key risk factor for the development of atherosclerosis. It is also predictive of an increased risk of atherothrombotic events (myocardial infarction, stroke). However, to date, no diagnostic tests have been developed for routine assessment of endothelial function. Increasing evidence has linked endothelin-1 (ET-1) expression to active coronary disease, and also to the development of heart failure. But short half-life and low stability mean ET-1 measurements are impractical and lack sensitivity as a diagnostic tool. The objective of this project is to establish a diagnostic biomarker assay based on the measurement of fragments of proendothelin-1, and to validate this assay using well characterised sets of patient samples.

Recent investigations have characterised the pattern of proendothelin-1 processing, and identified the main fragments secreted in cell culture. The goal of this project will be to use existing immunoassays for these fragments, in combination with modified immunoassays to detect degradation products, to assess the optimal fragment of proendothelin-1 to use as diagnostic marker of endothelin-1 synthesis. These assays will be validated in a two-step process. Firstly, immunoassays for all the processed fragments of proendothelin-1, as well as their degradation products, will be assessed using plasma samples from 500 well-characterised diabetic patients who were screened for CHD by electron-beam tomography and myocardial perfusion imaging at baseline and after 2.5 years follow up. This will identify the optimal assay specificity for determining level of disease, and disease progression. The second evaluation step will be to use the optimal assay methodology(s) to measure the baseline samples from the 20,536 people recruited to the Heart Protection Study. This will enable a detailed assessment of the prognostic value of proendothelin-1 measurements for predicting risk of vascular events or the development of heart failure.

Assay design is crucial to the success of this project. If the optimal assay methodology combines both novelty, and greater utility than competing ET-1 or proendothelin-1 assays, then it should be patentable, which will allow commercial exploitation. Commercialisation will be the best route for making this assay widely available for diagnostic purposes.