Transient increase in plasma oxidized LDL during the progression of atherosclerosis in apolipoprotein E knockout mice.

BACKGROUND Plasma level of oxidized low-density lipoprotein (OxLDL) is a risk marker for cardiovascular diseases. The behavior of plasma OxLDL before disease progression has not been studied previously. METHODS AND RESULTS In this study, we developed a sensitive ELISA procedure for detecting mouse circulating OxLDL using a monoclonal antibody that recognizes oxidized phosphatidylcholine and a rabbit antimouse apolipoprotein B-48 polyclonal antibody. Apolipoprotein E knockout mice were fed on a chow diet for 40 weeks. Oil red O-positive lesions developed gradually by 20 weeks, and the percentage area covered by the lesions increased dramatically after 28 weeks; it covers 33.4% of the surface area by 40 weeks. The OxLDL level, measured after LDL fraction was isolated from each mouse, at 10 weeks was 0.015 ng/microg LDL. It increased 3-fold at 20 weeks of age and then decreased to the basal level by 40 weeks of age, suggesting that OxLDL appears before the development of atherosclerotic lesions. The occurrence of lipid peroxidation products, acrolein and oxidized phosphatidylcholines, in aortic tissue were revealed by immunohistochemical staining as early as 10 weeks. CONCLUSIONS These results suggest that OxLDL might be involved in the early stages of progression of atherosclerotic lesions.