Modification of Apolipoprotein A-I in high density lipoproteins

High plasma concentrations of high density lipoproteins (HDL) cholesterol and apolipoprotein A-1 (apoA-I) are associated with a decreased risk for the development of coronary artery disease. Both the central role of HDL in reverse cholesterol transport and HDL`s ability to remove and detoxify potentially atherogenic, oxidized lipids are thought to be responsible for this. The earliest stage of oxidation of high-density lipoproteins (HDL) is accompanied by the oxidation of specific Met residues of apolipoprotein A-I i.e., apoA-I +32 , containing two methionine sulfoxide (Met(O)) in place of methionine (Met) residues. This has been shown to be linked to the reduction and hence detoxification of lipid hydroperoxides. The work carried out during the past year demonstrates that apoA-I +32 has a greater ability than native apoA-I to promote the efflux of lipids such as cholesterol, phospholipids, and a -tocopherol from lipid-laden human monocyte-derived macrophages (hMDM). These results suggest that selective oxidation may enhance rather than decrease potential anti-atherogenie properties of apoA-I. The aims of the proposed follow-up studies are to extend the characterization of potential biological functions of apoA-I +32 to the secretion of apolipoprotein E (apoE) from lipid-Iaden hMDM. In addition, the relative contribution of membranous cholesterol versus that accessibte to acyl coenzyme CoA:cholesterol acyl transferase to the cholesterol removed by apoA-I +32 will be investigated. Further experiments will establish a method for the isolation and initial characterization of human atherosclerotic lesion HDL and whether apoA-I +32 is present in human lesion HDL. And finally, we plan to evaluate for the first time whether the ability of lesion HDL to promote cholesterol efflux from human lipid-laden cells is altered compared to that of plasma HDL.