BACKGROUND:

Angiotensin converting enzyme (ACE) inhibition improves endothelial function and reduces the risk of acute myocardial infarction in patients with risk factors for coronary artery disease. The current study is based on data from this laboratory that suggest that bradykinin contributes to the favorable cardiovascular effects of ACE inhibitors by increasing tissue-type plasminogen activator (t-PA) release and improving fibrinolytic balance. For example, we have shown that endogenous bradykinin contributes to the hemodynamic effects of acute ACE inhibition. Bradykinin stimulates t-PA release from human vasculature through a B2 receptor-dependent, but nitric oxide synthase- and cyclooxygenase-independent pathway. This response is similar in black and white Americans, but preliminary data suggest that the t-PA response to bradykinin is greater in women compared to men. Bradykinin-stimulated t-PA release is impaired in smokers, while ACE inhibition increases constitutive vascular t-PA release in smokers through endogenous bradykinin. Conversely the ACE deletion allele, associated with increased ACE activity and cardiovascular mortality, is also associated with increased degradation of bradykinin; preliminary data suggest that this polymorphism interacts with B 2 receptor polymorphisms to modulate bradykinin-stimulated vasodilation and t-PA release.

DESIGN NARRATIVE:

The central hypothesis of the mechanistic studies is that genetic or environmental factors that decrease ACE activity and bradykinin degradation or that increase bradykinin receptor sensitivity favorably alter cardiovascular morbidity and mortality by enhancing the effect of bradykinin on fibrinolytic balance. In Specific Aim 1, the investigators will test the hypothesis that female gender enhances the effect of endogenous bradykinin on vascular t-PA release during ACE inhibition through effects of estrogen. In Specific Aim 2, they will test the hypothesis that 58C/T and BE1 polymorphisms in the B 2 receptor affect constitutive and bradykinin-stimulated t-PA release during ACE inhibition, and interact with the ACE insertion/deletion polymorphism in the absence of ACE inhibition. In Specific Aim 3, they will extend their prior studies to test the hypothesis that simultaneous inhibition of ACE and neutral endopeptidase (NEP) potentiates the vasodilator and fibrinolytic effects of bradykinin to a greater extent than ACE inhibition alone. It is expected that these pharmacogenetic studies will yield critical new information and strategies for enhancing the favorable effect of the kallikrein-kinin system on fibrinolysis and the risk of thrombotic cardiovascular events.

The studies are acute pharmacology studies examining the effect of ACE inhibition on vasodilatation and fibrinolytic pathways over a short time course. Volunteer subjects will have bilateral; intravenous catheters placed as well as a brachial arterial line. In each Specific Aim subjects will undergo randomized infusion of methacholine, NO donor SNP, or bradykinin in the presence and absence of ACE inhibition. Forearm blood flow, t-PA, and PAI-1 levels will be measured. In Specific Aim 1 the above experiments are to be performed in female smokers and non-smokers and compared to an age matched group of males. The purpose of this set of experiments is to define the effect of estrogen on FBF, and t-PA/PAI-1 levels following ACE inhibition. This Specific aim will require the enrollment of 48 subjects. These studies are each performed over a time course of 4 hours. It is unclear if the ACE inhibition effect is specific to the intravenous delivery of enalaprilat. Studies performed before and after the administration of an oral ACE inhibitor would be appropriate.

Specific Aim 2 to identify polymorphisms in the ACE and B2R genes that could modify the bradykinin-mediated regulation of t-PA/PAI-1 levels following ACE inhibition is independent and unrelated to specific aim 1. This is an ambitious specific aim in which the investigator plans to enroll 500 subjects over a five-year period all of whom will undergo the protocol as described above. Because there is no time line included in the proposal it is unclear but it appears both specific aim 1 and number 2 will need to be performed simultaneously.

Specific Aim 3 is unrelated to the preceding specific aims. The investigator plans to study the effect of simultaneously blocking neutral endopeptidase and ACE compared to ACE inhibition alone on both vasodialation and fibrinolytic responses. These studies will lead to novel findings regarding the effect of combined ACE/NEP inhibition versus ACE inhibition alone on the vasodilator and fibrinolytic response. These studies will require 64 patients. By combining all subjects from each of the specific aims this would amount to over 600 subjects. This does not include the subjects in specific aim 1 which will return for repeat studies.