DISTRIBUTION OF PAF-ACETYLHYDROLASE ACTIVITY IN HUMAN PLASMA LOW-DENSITY-LIPOPROTEIN SUBFRACTIONS

The distribution of PAF-acetylhydrolase (PAF-AH) activity in 3 LDL sub fractions prepared by density gradient ultracentrifugation as well as the rate of phosphatidylcholine (PC) hydrolysis during oxidation was s tudied. PAF-AH activity, measured before oxidation, was much higher in LDL(3) subfraction (28.4 +/- 8.6 nmol/mg per min) comparing to LDL(2) (14.1 +/- 5.8 nmol/mg per min), and to LDL(1), 8.7 +/- 3.7 nmol/mg pe r min. During oxidation, the enzyme activity was continuously decrease d and this phenomenon was more pronounced in LDL(1). PC hydrolysis was studied measuring the lyso-PC production expressed as lyso-PC/Sph mol ar ratio. Before oxidation, the lyso-PC/Sph molar ratio, did not diffe r significantly among the LDL subfractions, whereas, 4 h after the ons et of oxidation, it was significantly higher in LDL(2) and LDL(3) subf ractions (0.42 +/- 0.12 and 0.45 +/- 0.10, respectively), comparing to LDL(1) (0.29 +/- 0.06). Our results show that the distribution of PAF -AH activity in LDL subfractions is heterogeneous (mainly distributed in LDL(2) and LDL(3) subfractions) and it is positively correlated wit h higher lyso-PC production in those subfractions during oxidation. Th e contribution of this phenomenon to the enhanced susceptibility to ox idation as well as to the higher atherogenicity of the dense LDL subfr actions is under investigation.