title: Increased activity of platelet-activating factor acetylhydrolase in low-density lipoprotein subfractions induces enhanced lysophosphatidylcholine production during oxidation in patients with heterozygous familial hypercholesterolaemia.
abstract: Patients with heterozygous familial hypercholesterolaemia (FH) have elevated plasma concentrations of low-density lipoprotein (LDL) and develop premature atherosclerosis. There is increasing evidence that oxidative modification of LDL is important for the pathogenesis of atherosclerosis, and the LDL-associated platelet-activating factor acetylhydrolase (PAF-AH) seems to play a key role in LDL oxidation by hydrolysing the oxidized phospholipids of phosphatidylcholine (PC) and producing lysophosphatidylcholine (lyso-PC). We measured the total serum and high-density lipoprotein (HDL) levels of PAF-AH activity and studied the distribution of PAF-AH activity among three LDL subfractions isolated by gradient ultracentrifugation in 15 patients with heterozygous FH and 13 normolipidaemic control subjects. We also determined the lyso-PC production in each LDL subfraction during Cu2(+)-induced oxidation in vitro. The total serum PAF-AH activity in heterozygous FH patients was significantly higher than in control subjects, whereas the HDL-associated PAF-AH activity, expressed as a percentage of total serum PAF-AH activity, was significantly lower in the FH patients than in control subjects (13.9 +/- 6.6% vs. 30.6 +/- 4.4%, P < 0.001). Among the LDL subfractions, the PAF-AH activity in both normolipidaemic control subjects and FH patients, expressed as nmol mg-1 protein min-1, was significantly higher in the LDL3 subfraction (33.1 +/- 4.8 and 53.4 +/- 11.5 respectively) than in the LDL2 (18.6 +/- 5.3 and 26.8 +/- 10.4 respectively, P < 0.0001 for both comparisons) and LDL1 subfractions (5.1 +/- 1.5 and 7.8 +/- 2.6, respectively, P < 0.0001 for both comparisons). Additionally, the enzyme activity in each LDL subfraction of the heterozygous FH patients was significantly higher than in control subjects (P < 0.02 for LDL1, P < 0.03 for LDL2 and P < 0.0001 for LDL3). No difference was observed in the susceptibility to oxidation of each LDL subfraction among the heterozygous FH patients and the normolipidaemic control subjects. During oxidation, the PAF-AH activity decreased, whereas the lyso-PC levels significantly increased in all subfractions of both groups. The lyso-PC/sphingomyelin molar ratio in each LDL subfraction of the FH patients 3 h after the onset of the oxidation was significantly higher than in control subjects [0.38 +/- 0.05 and 0.27 +/- 0.04, respectively, for LDL1 (P < 0.006), 0.47 +/- 0.08 and 0.39 +/- 0.03, respectively, for LDL2 (P < 0.04), 0.55 +/- 0.11 and 0.42 +/- 0.06, respectively, for LDL3 (P < 0.02)]. Our results show that heterozygous FH patients exhibit higher PAF-AH activity than control subjects in all LDL subfractions, resulting in higher lyso-PC production during oxidation, which confers on these subfractions higher biological potency. This phenomenon, in combination with the diminished anti-atherogenic and antioxidant capability of HDL in these patients due to the relatively low HDL-cholesterol levels compared with LDL-cholesterol levels and, consequently, the relatively low HDL-associated PAF-AH activity, could contribute to the higher atherogenicity and incidence of coronary artery disease observed in FH patients.
authors.affiliation: Department of Chemistry, Medical School, University of Ioannina, Greece.
authors.forename: S A
authors.initials: SA
authors.lastname: Karabina
authors.forename: M
authors.initials: M
authors.lastname: Elisaf
authors.forename: E
authors.initials: E
authors.lastname: Bairaktari
authors.forename: C
authors.initials: C
authors.lastname: Tzallas
authors.forename: K C
authors.initials: KC
authors.lastname: Siamopoulos
authors.forename: A D
authors.initials: AD
authors.lastname: Tselepis
mesh_terms: D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase; D000293:Adolescent; D000328:Adult; D005591:Chemical Fractionation; D005260:Female; D006579:Heterozygote; D006801:Humans; D006938:Hyperlipoproteinemia Type II / Q000097:blood* / Q000201:enzymology* / Q000235:genetics; D008077:Lipoproteins, LDL / Q000097:blood* / Q000737:chemistry; D008244:Lysophosphatidylcholines / Q000096:biosynthesis* / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D010741:Phospholipases A / Q000097:blood*
chemical_list: D008077:Lipoproteins, LDL; D008244:Lysophosphatidylcholines; D010741:Phospholipases A; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase