Paraoxonase: The universal factor of antioxidant defense in Human Body
The paraoxonase (PON) gene family includes three members: PON1, PON2, and PON3 aligned in tandem on chromosome 7 in humans. All PON proteins share considerable structural homology and have the capacity to protect cells from oxidative stress; therefore, they have been implicated in the pathogenesis of several inflammatory diseases, particularly atherosclerosis. Increased production of reactive oxygen species as a result of decreased activities of mitochondrial electron transport chain complexes plays a role in the development of many inflammatory diseases, including atherosclerosis. PON1 and PON3 proteins can be detected in plasma and reside in the high-density lipoprotein fraction and protect against oxidative stress by hydrolyzing certain oxidized lipids in lipoproteins, macrophages, and atherosclerotic lesions. Paraoxonase 2 (PON2) possesses antiatherogenic properties and is associated with lower ROS levels. PON2 is involved in the antioxidative and anti-inflammatory response in intestinal epithelial cells. In contrast to PON1 and PON3, PON2 is cell-associated and is not found in plasma. It is widely expressed in a variety of tissues, including the kidney, and protects against cellular oxidative stress. Overexpression of PON2 reduces oxidative status, prevents apoptosis in vascular endothelial cells, and inhibits cell-mediated low density lipoprotein oxidation. PON2 also inhibits the development of atherosclerosis, via mechanisms involving the reduction of oxidative stress. In this review we explore the physiological roles of PON in disease development and modulation of PONs by infective (bacterial, viral) agents.