The oxidation of apolipoprotein B-containing lipoproteins and cell membrane lipids is believed to play an integral role in the development of fatty streak lesions, an initial step in atherogenesis. We have previously shown that two antioxidant-like enzymes, paraoxonase (PON)-1 and PON3, are high density lipoprotein-associated proteins capable of preventing the oxidative modification of low density lipoprotein (LDL) (Reddy, S. T., Wadleigh, D. J., Grijalva, V., Ng, C., Hama, S., Gangopadhyay, A., Shih, D. M., Lusis, A. J., Navab, M., and Fogelman, A. M. (2001) Arterioscler. Thromb. Vasc. Biol. 21, 542-547). In the present study, we demonstrate that PON2 (i) is not associated with high density lipoprotein; (ii) has antioxidant properties; and (iii) prevents LDL lipid peroxidation, reverses the oxidation of mildly oxidized LDL (MM-LDL), and inhibits the ability of MM-LDL to induce monocyte chemotaxis. The PON2 protein was overexpressed in HeLa cells using the tetracyclineinducible ("Tet-On") system, and its antioxidant capacity was measured in a fluorometric assay. Cells that overexpressed PON2 showed significantly less intracellular oxidative stress following treatment with hydrogen peroxide or oxidized phospholipid. Moreover, cells that overexpressed PON2 were also less effective in oxidizing and modifying LDL and, in fact, were able to reverse the effects of preformed MM-LDL. Our results suggest that PON2 possesses antioxidant properties similar to those of PON1 and PON3. However, in contrast to PON1 and PON3, PON2 may exert its antioxidant functions at the cellular level, joining the host of intracellular antioxidant enzymes that protect cells from oxidative stress.
Oxidation of low density lipoproteins (LDL)1 trapped in the arterial subendothelial space is a key process in atherosclerotic lesion development. High density lipoprotein (HDL) inhibits LDL oxidation (1-4) and prevents the synthesis and secretion of monocyte chemotactic protein-1 by artery wall cells, thereby blocking the recruitment and transmigration of monocytes though the arterial endothelial layer (5). The anti-atherogenic properties associated with HDL are due, at least in part, to the activity of HDL-associated enzymes, which interact with LDL and prevent and/or reverse its oxidation (6). The calcium-dependent ester hydrolase paraoxonase (PON)-1 (EC 3.1.8.1) is one of several such enzymes and is found tightly associated with apoA-I in the HDL particle (7). Purified PON1 not only prevents LDL oxidation (8), but also blocks the ability of mildly oxidized LDL (MM-LDL) to induce monocyte chemotaxis and binding to endothelial cells (9). Epidemiological studies have shown that PON1 polymorphisms are correlated with variations in plasma lipoprotein levels (10) and coronary artery disease in some populations (11-15). In addition, Mackness et al. (16) showed that alloenzymes of PON1 determine the effectiveness of HDL in the protection of LDL from lipid peroxidation. Two other members of the PON gene family, termed PON2 and PON3, have been identified...
