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...

Atividade da enzima acetil-hidrolase do fator ativador de plaquetas (PAF-AH) em pacientes com diabete melito tipo 1

“…The stepwise multiple regression using PAF-AH activity as a dependent variable and age, gender, BMI, HbA1c, HDL and LDL as independent variables showed HDL and LDL as independent explanatory variables of changes in PAF-AH activity (step 1: r = 0.231, r2 studied, Cavallo-Perin et al 28 and Nathan et al 27 demonstrated that PAF levels are increased in patients with DM 1, and that this would be basically associated with a higher production of this particle. The disagreement between data found by these authors and our own may reflect the characteristics of the population studied -our sample had a lower age range, no microvascular complications and lower BMI, as well as the sample size -42 diabetics versus 7 patients with microalbuminuria and 7 without microalbuminuria assessed by Cavallo-Perin et al The higher PAF-AH activity in patients with DM 1 may represent an attempt at protection against pathophysiological mechanisms induced by increased levels of PAF found in these patients 34 or may exert pro-inflammatory and pro-atherogenic effects 30,32,33 .…”

“…There is controversy in the literature regarding the importance of the PAF-AH activity and concentration in the atherosclerotic process [27][28][29][30][31][32][33] . Some studies demonstrate that patients with DM 1 have low levels of PAF-AH, unlike patients with DM 2 27,29 .…”

Modulation of oxidative stress, inflammation, and atherosclerosis by lipoprotein-associated phospholipase A2

“…26 ). Differential distribution of Lp-PLA 2 in various plasma lipoproteins may affect its function (35)(36)(37)(38), and thus much effort has been spent elucidating is to ensure that the redox state of the cell remains within viable parameters. In addition to the multiplicity of compensatory responses, individual pathways are biochemically, genetically, and epigenetically regulated by diverse stimuli, environmental cues, receptor ligands, and transcriptional activators whose concentrations are constantly changing to meet homeostatic demands ( 7 ).…”

Identification of a Domain That Mediates Association of Platelet-activating Factor Acetylhydrolase with High Density Lipoprotein

“…These findings led to the identification of PAF-AH domains essential for the human enzyme to associate with LDL (7). A number of clinical studies from various laboratories indicate that altered location of PAF-AH correlates with human diseases such as coronary artery disease (8), hypercholesterolemia (9), paroxysmal atrial fibrillation (10), and chronic kidney disease (11). These observations suggest that the distribution of PAF-AH in lipoproteins may define its physio-pathological function in humans.…”