The study investigates the role of paraoxonase (PON) in protecting high-density lipoprotein (HDL) from oxidation and preserving its functions. PON, an enzyme associated with HDL, was found to inhibit copper-induced HDL oxidation in a concentration-dependent manner. When added to HDL, PON prolonged the oxidation lag phase and reduced peroxide and aldehyde formation by up to 95%. PON enrichment in serum HDL increased its resistance to oxidation, and PON inhibitors enhanced HDL oxidizability. PON also protected HDL from oxidative damage by inhibiting the formation of lipid peroxides and cholesteryl linoleate hydroperoxides, demonstrating peroxidase-like activity. In apolipoprotein E-deficient mice, serum PON activity decreased with age, coinciding with increased atherosclerotic lesion progression and lipid peroxidation. The findings suggest that HDL-associated PON plays a crucial role in maintaining HDL's anti-atherogenic properties by inhibiting HDL oxidation and preserving its ability to induce cellular cholesterol efflux.The study investigates the role of paraoxonase (PON) in protecting high-density lipoprotein (HDL) from oxidation and preserving its functions. PON, an enzyme associated with HDL, was found to inhibit copper-induced HDL oxidation in a concentration-dependent manner. When added to HDL, PON prolonged the oxidation lag phase and reduced peroxide and aldehyde formation by up to 95%. PON enrichment in serum HDL increased its resistance to oxidation, and PON inhibitors enhanced HDL oxidizability. PON also protected HDL from oxidative damage by inhibiting the formation of lipid peroxides and cholesteryl linoleate hydroperoxides, demonstrating peroxidase-like activity. In apolipoprotein E-deficient mice, serum PON activity decreased with age, coinciding with increased atherosclerotic lesion progression and lipid peroxidation. The findings suggest that HDL-associated PON plays a crucial role in maintaining HDL's anti-atherogenic properties by inhibiting HDL oxidation and preserving its ability to induce cellular cholesterol efflux.