Abstract 3: Site-Specific Chlorination of ApoA-I, the Major HDL Protein, Is Associated with Impaired Sterol Efflux and Is Markedly Increased in Subjects with Coronary Artery Disease

Abstract

3-Chlorotyrosine is a specific product of myeloperoxidase (MPO), a heme protein expressed by macrophages in human atherosclerotic lesions. We have previously shown in vitro that chlorination of Tyr192 (3-chloroTyr192) together with methionine oxidation of lipid-free apoA-I impairs the apolipoprotein’s ability to promote cholesterol efflux from macrophages by the ABCA1 pathway. Using a sensitive and quantitative LC-MS/MS approach with selected reaction monitoring (SRM), we have recently demonstrated that Tyr192 is the major site of chlorination in apoA-I of HDL isolated from human atherosclerotic lesions. In a prospective study, we determined if: i) MPO contributes to the chlorination of apoA-I in circulating HDL; and ii) 3-chloroTyr192 serves as a marker for clinically significant cardiovascular disease. We quantified HDL oxidation and sterol efflux in three groups: i) stable CAD subjects, ii) acute coronary syndrome (ACS) subjects, and iii) healthy control subjects (N=20 per group). SRM analysis demonstrated that levels of 3-chloroTyr192 were markedly elevated in HDL isolated from subjects with CAD or ACS (p=0.009 and p=0.01 vs. control subjects, respectively). A key cardioprotective effect of HDL is its ability to promote cholesterol efflux from macrophages by the ABCA1 pathway. We found that the ABCA1-dependent sterol efflux capacity of HDL isolated from CAD and ACS subjects was significantly impaired. Importantly, sterol efflux capacity associated inversely with levels of 3-chloroTyr192 (R=-0.30, p=0.02), suggesting that oxidation of HDL by MPO contributes to the impaired cholesterol efflux capacity of HDL. Receiver operating characteristic curve analysis revealed that levels of 3-chloroTyr192 distinguished between CAD or ACS subjects and control subjects (AUC 0.76, p=0.0008 and AUC 0.73, p=0.004, respectively). These observations strongly suggest that MPO contributes to the generation of dysfunctional HDL in subjects with clinically significant atherosclerosis. They further indicate that quantification of 3-chloroTyr192 levels in HDL may provide a new approach to the diagnosis and treatment of CAD and ACS.