Insight into the Mode of Action of ACE Inhibition in Coronary Artery Disease

Abstract

ACE inhibition is now recognized as superior to placebo on outcomes in stable coronary artery disease (CAD), including total and cardiovascular mortality, fatal and nonfatal myocardial infarction, heart failure, revascularization and stroke. This review examines clinical evidence for the mode of action of ACE inhibitors in CAD, which is dominated by the results of a single trial, EUROPA, and its substudies. The generally accepted mode of action for ACE inhibitors in CAD is blood pressure reduction. However, the EUROPA data demonstrate that endothelial protection, with the effect of arresting or reducing the processes of atherosclerosis is also important. Chronic overexpression of tissue ACE in CAD disrupts the angiotensin II/bradykinin balance with a net result of endothelial dysfunction. ACE inhibitors reduce production of angiotensin II, which prevents vasoconstriction, reduces adhesion molecules and growth factors, decreases oxidative stress and prevents apoptosis. A concomitant decrease in the degradation of bradykinin as a result of ACE inhibition raises levels of this kinin, leading to vasodilation and an antiapoptotic action, as well as opposition of the negative actions of angiotensin II. We now have clinical trial evidence of these processes in CAD patients participating in the EUROPA study by measurement of markers of endothelial function, including nitric oxide synthase (eNOS), the rate of apoptosis and levels of von Willebrand factor (vWf). Serum from CAD patients was found to significantly downregulate eNOS protein expression and activity versus that of healthy controls (p < 0.01), most probably as a result of upregulation of tissue ACE. One year of treatment with perindopril upregulated eNOS protein expression and activity (19% and 27% vs placebo; p < 0.05). Similarly, vWf was elevated at baseline and significantly reduced after 1 year of treatment with perindopril (p < 0.001). Increased endothelial apoptosis by serum of CAD patients was accompanied by excess angiotensin II and tumour necrosis factor-alpha and a reduction in bradykinin; all of these parameters were reversed by treatment. We therefore have clinical results showing that perindopril normalizes the angiotensin II/bradykinin balance, reduces inflammation and prevents endothelial apoptosis. Accumulating preclinical evidence for the absence of a class effect for ACE inhibitors includes differences in terms of effect on eNOS and rate of endothelial apoptosis. These differences appear to be related to tissue affinity, penetration of atherosclerotic plaque and affinity for the target enzyme. Consideration of these features is important when administering ACE inhibition as secondary prevention in CAD patients. In this context, current European guidelines for stable angina pectoris recommend prescription of agents and doses with proven efficacy in secondary prevention.