|M.Sc Student||Rozenberg Orit|
|Subject||The Effect of Paraoxonase (PON1) on Macrophage Oxidative|
Status and Cholesterol Biosynthesis
|Department||Department of Medicine||Supervisor||Professor Emeritus Michael Aviram|
Human serum paraoxonase (PON1) is an esterase whose activity is inversely related to the atherosclerotic lesion development, which contains cholesterol-loaded macrophage foam cells. The aim of the present study was to examine whether the anti-atherogenic properties of PON1 are related to its capacity to reduce oxidative stress and cholesterol biosynthesis in macrophages. For this purpose we used mouse peritoneal macrophages (MPM) harvested from PON1-deficient and from control mice. PON1-deficient mice exhibited a significantly 51% increased atherosclerotic lesion area and a 35% higher macrophage cholesterol content, compared to control mice. Macrophage lipid peroxides content and macrophage capacity to oxidize LDL were increased in PON1-deficient mice MPM, compared control mice MPM. Moreover, increased release of macrophage superoxide anion from PON1-deficient MPM as well as increased activation of the NADPH oxidase enzyme were noticed. Furthermore, purified human PON1 was found to directly decrease, peroxides content (by 18%), macrophage superoxide anion release (by 33%) and macrophage-mediated oxidation of LDL (by 22%) in PON1-deficient mice MPM.
We found that the macrophage cholesterol biosynthesis was increased in MPM from PON1-deficient mice by 50%, compared to their controls. Human PON1 resulted in a dose-dependent decrease (40% - 84%) in macrophage cholesterol biosynthesis in MPM from PON1-deficient and control mice. We observed a PON1 phospholipase-A2-like activity on MPM, as evidenced by formation of lysophosphatidylcholine. Upon incubation of macrophages with lysophosphatidylcholine, a dose-dependent inhibition of cellular cholesterol biosynthesis was noted. We thus concluded that PON1-deficiency results in increased macrophage oxidative stress and macrophage cholesterol biosynthesis in PON1-deficient mice, and that PON1 can also directly decreases macrophage oxidative stress and cholesterol biosynthesis, major processes that induce foam cell formation and atherosclerosis progression.