Anti-atherogenic properties of paraoxonase 2 and paraoxonase 3: In vitro and in vivo studies

Initially discovered for its ability to hydrolyze organophosphates, the study of paraoxonase (PON)1 has branched out into the field of cardiovascular diseases. Epidemiologic, genetic, and biochemical studies have supported a protective role for PON1 in atherogenesis. PON1 however, is just one member of a multigene gene family that also includes PON2 and PON3. In contrast to PON1, little is known about the function of PON2 or PONS. Based on their high homology to PON1, we hypothesized that PON2 and PON3 may also possess antioxidant/anti-inflammatory properties and play a protective role in atherogenesis. To test this hypothesis, stable cell lines capable of overexpressing PON2 or PON3 were generated. Using these cells, we demonstrated that similar to PON1, PON2 and PON3 exhibited antioxidant/anti-inflammatory properties and were capable of protecting against LDL oxidation, an integral initial step in atherogenesis. To confirm these findings in vivo, we used adenoviral vectors to overexpress PON2 (AdPON2) or PON3 (AdPON3) in a mouse model of atherosclerosis. Mice treated with AdPON2 or AdPON3 developed significantly lower levels of atheroma compared to their control counterparts. Serum from mice treated with AdPON2 or AdPON3 contained significantly lower levels of lipid hydroperoxides and exhibited an enhanced ability to efflux cholesterol from cholesterol loaded macrophages. In addition, LDL and HDL isolated from AdPON2 or AdPON3 treated mice exhibited enhanced anti-inflammatory properties, inducing significantly less monocyte chemotaxis relative to their control counterparts. These studies demonstrated that a transient increase in PON2 or PON3 can protect against atherogenesis. For long term studies, PON2 and PON3 knockout and transgenic mice were to be used. Currently, PON2 transgenic, PON3 knockout, and PON3 transgenic mice are being tested/developed. PON2 knockout mice however, have been generated, and studies using these mice have confirmed our previous findings. PON2-deficient mice exhibited a significantly higher mortality rate compared to their wildtype counterparts in an endotoxemia model of acute systemic inflammation. In addition, when placed on an atherogenic diet, PON2-deficient mice developed significantly higher levels of atheroma compared to their wildtype counterparts. These studies demonstrate that PON2 indeed possesses anti-inflammatory properties and can protect against both acute and chronic inflammatory processes.