Haem-Enzymes Predictive of Coronary Artery Disease Are Present in Thoracic and Abdominal Aortic Aneurysm

Abstract

Purpose: A reliable plasma biomarker for aortic aneurysm has proven elusive. Elevated plasma levels of the oxidative or immune regulatory haem-enzymes myeloperoxidase (MPO) or indoleamine 2,3-dioxygenase (IDO) can predict disease prevalence and clinical risk in coronary artery disease patients. We therefore studied the relationship of MPO and IDO with thoracic or abdominal aortic aneurysm. Methodology: In patients undergoing elective surgical or endovascular repair of thoracic (n = 14) or abdominal (n = 18) aortic aneurysm, preoperative plasma was analysed for MPO protein levels by ELISA or IDO activity (indexed as a ratio of IDO's product kynurenine and substrate tryptophan) and compared with healthy controls (n = 15). Plasma levels of other inflammatory markers (CRP, neutrophil elastase) were also measured. Surgically resected aortic wall samples were analysed for MPO protein by immunohistochemistry. Results: Patients with abdominal aneurysms [72 yrs (67-76)] were significantly older than those with thoracic aneurysms [57 yrs (52-70)] and healthy controls [31 years (29-36)] and more likely to have atherosclerosis as the aetiology of aortic disease (88.9% vs. 28.6% in thoracic aneurysm). Plasma IDO activity and CRP levels, but not MPO or elastase, were significantly elevated in patients with aortic aneurysm vs. healthy controls. MPO protein, however, was expressed in the intima and media of all aortic aneurysm specimens but not non-diseased aorta. Conclusion: The haem-enzymes MPO and IDO may be involved in human aortic aneurysm and their roles warrant further study in experimental animal models of aneurysm. Measurement of plasma IDO activity and CRP, but not MPO, may represent potential useful biomarkers for aortic aneurysm.