Despite the many links between myeloperoxidase (MPO), oxidant stress, and the evolution of atherosclerotic coronary artery disease (CAD), many critical questions remain. For example, a direct demonstration of a causal role for MPO in atherosclerotic CAD in humans is not yet established. Moreover, mechanisms for regulating MPO in vivo remain unknown. The present application represents a logical progression of our studies and a direct effort to address these important questions. It is predicated upon the hypothesis that MPO and its newly discovered interactions with the HDL associated protein paraoxonase 1 (PON1) are genetically and mechanistically linked to oxidative stress and the development of cardiovascular disease. It integrates studies on basic mechanisms of action, interaction and molecular structure along with a search for specific reaction products to reveal whether relevant pathways operate in human disease, and in animal models of inflammation and cardiovascular disorders. The overall goals of this proposal are to: (i) define at both the structural and functional level MPO interactions with the HDL associated protein P0N1 and the reciprocal effects of MPO and PON1 on the regulation of each other's catalytic activity; and (ii) use a combination of genetic and biochemical approaches to explore the role of MPO, PON1 and specific oxidation pathways in development of CVD. We will achieve this through the following specific aims: Aim 1) We will testing the hypothesis that MPO, HDL and PON1 form a functional ternary complex that plays a role in the reciprocal regulation of MPO and PON1 activities in vivo. Aim 2) We will test the hypothesis that genetic and biochemical determinants of MPO and PON1 are linked to oxidant stress and coronary atherosclerotic plaque development, progression and adverse cardiac events in vivo. Collectively, the proposed studies represent an integrated, multidisciplinary and systematic approach designed to elaborate mechanisms linking MPO, oxidant stress and atherogenesis. The proposed studies will provide new insights into clinically important questions investigating a potential causal role of MPO and oxidant stress in atherogenesis. Successful completion of these studies will help discover key structural and functional relationships linking MPO with risks for development of prevalent cardiovascular disease, plaque progression and major adverse cardiovascular events.