Paraoxonase 1 (PON1) is present in postprandial chylomicrons.

Paraoxonase 1 (PON1) is an esterase, associated in serum with high density lipoprotein (HDL). As diet affects serum PON1 activity, we questioned whether PON1 is also carried by postprandial chylomicrons. Chylomicrons were isolated by ultracentrifugation from plasma of 10 healthy men, 3h after the consumption of a high fat, high carbohydrate meal, and were analyzed for the presence of PON1 arylesterase activity and protein. The present study shows for the first time that, in addition to the presence of PON1 mainly on HDL, postprandial chylomicrons also contain minor, but significant amount of PON1. PON1 was also present in chylomicrons derived from fasted patients with hyperchylomicronemia. In addition, PON1 was detected in very low density lipoprotein (VLDL), but not in LDL. The origin of chylomicron PON1 could be partly attributed to its transfer from HDL. Finally, this study demonstrates that postprandial chylomicrons inhibit copper ion-induced LDL oxidation, secondary to hydrolysis of lipid peroxides, a phenomenon which could be related, at least in part, to the chylomicron PON1 content. We conclude that postprandial chylomicrons contain PON1, which may function in the removal of atherogenic oxidized lipids.