Reduced postprandial serum paraoxonase activity after a meal rich in used cooking fat

Paraoxonase is an enzyme associated with HDL in human serum that:hydrolyzes oxidized phospholipids and inhibits LDL oxidation, which is an important s tep in atherogenesis. In animals, addition of oxidized Lipids to the circul ation reduces paraoxonase activity, and diets rich in oxidized fat accelera te the development of atherosclerosis. The current randomized, crossover st udy was designed to compare the effect of a meal rich in oxidized lipids in the form of fat that had been used for deep-frying in a fast food restaura nt and a control meal rich in the corresponding unused fat on postprandial serum paraoxonase (arylesterase) activity and peroxide content of LDL and i ts susceptibility to copper ion catalyzed oxidation in 12 healthy men. Four hours into the postprandial period, serum paraoxonase activity had decreas ed significantly after the used fat meal (-17%, P=0.005) and had increased significantly after the meal rich in unused fat (14%, P=0.005). These chang es were significantly (P=0.003) different. A time-course study indicated th at serum paraoxonase activity remained lower than baseline for up to 8 hour s after the used fat meal. Serum apoA1 concentration tended to decrease aft er the unused fat meal and tended to increase after the used fat meal. Thes e changes were different at a marginal level of significance (P=0.07). Also , a significantly (P=0.03) greater decrease in apoA1 content of postprandia l HDL was recorded after the unused fat meal. The peroxide content. of LDL tended to decrease after the used fat meal and tended to increase after the control meal. These changes were significantly (P=0.04) different. Suscept ibility of isolated LDL to copper ion oxidation and plasma levels of malond ialdehyde were unchanged during the study. These data suggest that in the p ostprandial period after a meal rich in used cooking fat, the enzymatic pro tection of LDL against accumulation of peroxides and atherogenic oxidative modification may be reduced, possibly due to factors associated with apoA1, without acutely affecting the intrinsic resistance of LDL to in vitro oxid ation.