Platelet-activating Factor Acetylhydrolase Activity Research Articles

M.574 The levels of autoantibodies against oxidized LDL in hypercholesterolemic patients are influenced by the LDL-associated PAF-acetylhydrolase activity

M.574 The levels of autoantibodies against oxidized LDL in hypercholesterolemic patients are influenced by the LDL-associated PAF-acetylhydrolase activity

Fluvastatin Slow-Release Lowers Platelet-Activating Factor Acetyl Hydrolase Activity: A Placebo-Controlled Trial in Patients with Type 2 Diabetes

Fluvastatin reduces atherogenic dense low-density lipoprotein (dLDL) in patients with type 2 diabetes mellitus (T2DM). dLDLs are associated with platelet-activating factor acetyl hydrolase (PAF-AH), an enzyme involved in inflammation and related to coronary artery disease (CAD). The association of preexisting CAD and PAF-AH and the effect of fluvastatin on enzyme activity is investigated in a placebo-controlled trial in patients with T2DM. A multicenter, double-blind, randomized comparison of fluvastatin XL (80 mg) (n = 42) and placebo (n = 47), each given once-daily for 8 wk, in 89 patients with T2DM, was conducted. At baseline and on treatment, lipoproteins, including lipoprotein (a) [Lp(a)] and LDL subfractions, and the activity of PAF-AH were measured. Increasing PAF-AH activity was significantly associated with a positive history of CAD (+0.7% per IU/liter PAH-AH; P = 0.010), the odds ratio estimate adjusted for age, gender, and body mass index of the highest quartile being 10.6 (P = 0.036). At baseline and at study end, PAF-AH activity was associated with the apolipoprotein B (apoB) content in dLDL (LDL-5 and LDL-6) (r = 0.447; P < 0.001 and r = 0.651; P < 0.001, respectively) and with non-HDL cholesterol at baseline (r = 0.485; P < 0.001). However, after additional adjustment for apoB in dLDL and non-HDL cholesterol at baseline, the odds ratio increment for CAD across PAF-AH quartiles was 2.09 (95% confidence interval, 1.02-4.29; P = 0.043). Fluvastatin treatment decreased the activity of PAF-AH by 22.8% compared with an increase of 0.4% in the placebo group (P < 0.001). This effect was independent of changes of Lp(a) concentrations. In patients with T2DM, PAF-AH activity is associated with a positive history of CAD. Fluvastatin not only decreases atherogenic dLDL but also PAF-AH activity, emphasizing the significance of fluvastatin treatment in T2DM. The antiatherogenic potential of fluvastatin in T2DM may thus be greater than expected from its effects on LDL-C and triglycerides alone.

1083-189 Modulating effects of cholesterol elevation by diet-feeding and cholesterol lowering by simvastatin on platelet-activating factor acetylhydrolase activity, paraoxonase activity, and lysophosphatidylcholine concentration

1083-189 Modulating effects of cholesterol elevation by diet-feeding and cholesterol lowering by simvastatin on platelet-activating factor acetylhydrolase activity, paraoxonase activity, and lysophosphatidylcholine concentration

Recombinant human platelet-activating factor acetylhydrolase for treatment of severe sepsis: Results of a phase III, multicenter, randomized, double-blind, placebo-controlled, clinical trial*

Platelet-activating factor (PAF) and structurally-related oxidized phospholipids are proinflammatory mediators in systemic inflammatory states such as severe sepsis. The enzyme platelet-activating factor acetylhydrolase (PAF-AH) rapidly degrades PAF and oxidized phospholipids into inactive metabolites. Reduced PAF-AH activity has been observed in patients with severe sepsis and may contribute to their systemic inflammatory response and organ dysfunction. A previous clinical trial with recombinant human PAF-AH (rPAF-AH, Pafase) suggested that this treatment may decrease 28-day all-cause mortality in patients with severe sepsis. The current study was undertaken to confirm this result. A prospective, randomized, double-blind, placebo-controlled, multicenter, international trial. One hundred forty-six intensive care units from nine countries. Approximately 2,522 patients were planned to be enrolled < or =12 hrs after the onset of severe sepsis. Eligible patients were randomized to receive either rPAF-AH 1.0 mg/kg or placebo administered intravenously once daily for five consecutive days. The study was terminated based on the recommendation of an independent data and safety monitoring committee after the second of three planned interim analyses, and the enrollment of 1,425 patients. rPAF-AH treatment was well tolerated among the 1,261 patients included in the interim analysis (643 rPAF-AH and 618 placebo), but did not decrease 28-day all-cause mortality compared with placebo (25% for rPAF-AH vs. 24% for placebo; relative risk, 1.03; 95% confidence interval, 0.85-1.25; p =.80). There were no statistically significant differences between treatment groups in any of the secondary efficacy end points. The overall incidence of adverse events was similar among rPAF-AH and placebo-treated patients, and no rPAF-AH-treated patients developed antibodies to PAF-AH. rPAF-AH was well tolerated and not antigenic, but did not decrease 28-day all-cause mortality in patients with severe sepsis.

Elevated plasma phospholipase A2 and platelet-activating factor acetylhydrolase activity in colorectal cancer.

This clinical study reports that blood levels of the pro-inflammatory mediator platelet-activating factor (PAF) did not change in colorectal cancer patients. In contrast, plasma levels of two enzymatic activities, one implicated in PAF production (i.e. phospholipase A2) and one in PAF degradation (i.e. PAF acetylhydrolase activity) were significantly elevated.

Inhibition of platelet-activating factor (PAF) acetylhydrolase by methyl arachidonyl fluorophosphonate potentiates PAF synthesis in thrombin-stimulated human coronary artery endothelial cells.

We have previously demonstrated that thrombin stimulation of endothelial cells results in increased membrane-associated, Ca(2+)-independent phospholipase A2 (iPLA2) activity, accelerated hydrolysis of membrane plasmalogen phospholipids, and production of several biologically active phospholipid metabolites, including prostacyclin and platelet-activating factor (PAF) that is abolished by pretreatment with the iPLA2-selective inhibitor bromoenol lactone. This study was designed to further investigate the role of alternative PLA2 inhibitors, including methyl arachidonyl fluorophosphonate (MAFP, an inhibitor of cytosolic PLA2 isoforms), on phospholipid turnover and PAF production from thrombin-stimulated human coronary artery endothelial cells (HCAECs). Paradoxically, pretreatment of HCAEC with MAFP (5-25 microM) resulted in a significant increase in PAF production in both unstimulated and thrombin-stimulated cells that was found to be a direct result of inhibition of PAF acetylhydrolase (PAF-AH) activity. Pretreatment with MAFP did not significantly inhibit HCAEC PLA2 activity, possibly due to the localization of PLA2 activity in the membrane fraction rather than the cytosol. Bromoenol lactone did not inhibit PAF-AH activity, even at concentrations as high as 20 microM. We conclude that MAFP augments thrombin-stimulated PAF production by inhibition of PAF catabolism without affecting membrane-associated iPLA2 activity.

Altered distribution of plasma PAF-AH between HDLs and other lipoproteins in hyperlipidemia and diabetes mellitus

Platelet-activating factor acetylhydrolase (PAF-AH) is a phospholipase A2 associated with lipoproteins that hydrolyzes platelet-activating factor (PAF) and oxidized phospholipids. We have developed an ELISA for PAF-AH that is more sensitive than previous methods, and have quantified HDL-associated and non-HDL-associated PAF-AH in healthy, hyperlipidemic, and diabetic subjects. In healthy subjects, plasma total PAF-AH concentration was positively correlated with PAF-AH activity and with plasma total cholesterol, triacylglycerol, LDL cholesterol and apolipoprotein B (apoB) concentrations (all P < 0.01). HDL-associated PAF-AH concentration was correlated positively with plasma apoA-I and HDL cholesterol. Subjects with hyperlipidemia (n = 73) and diabetes mellitus (n = 87) had higher HDL-associated PAF-AH concentrations than did controls (P < 0.01). Non-HDL-associated PAF-AH concentration was lower in diabetic subjects than in controls (P < 0.01). Both hyperlipidemic and diabetic subjects had lower ratios of PAF-AH to apoB (P < 0.01) and higher ratios of PAF-AH to apoA-I (P < 0.01) than did controls. Our results show that the distribution of PAF-AH mass between HDLs and LDLs is determined partly by the concentrations of the lipoproteins and partly by the mass of enzyme per lipoprotein particle, which is disturbed in hyperlipidemia and diabetes mellitus.

The PON1 M55L gene polymorphism is associated with reduced HDL-associated PAF-AH activity

The platelet-activating factor acetylhydrolase activity associated with high density lipoprotein (HDL-PAF-AH) may substantially contribute to the antioxidant, anti-inflammatory, and overall antiatherogenic effects of HDL. Two enzymes associated with HDL express PAF-AH catalytic activity, PAF-AH itself and paraoxonase-1 (PON1). The relative contribution of these enzymes in the expression of PAF-AH activity on HDL remains to be established. We investigated whether the PON1 polymorphisms (M55L and Q192R) or the PAF-AH polymorphism V379A could affect the PAF-AH activity associated with HDL in both normolipidemic and dyslipidemic (type IIA and IIB) populations. We show for the first time that the PON1 M55L polymorphism significantly affects the HDL-PAF-AH activity in all studied groups, the PON1 L55L individuals having lower enzyme activity compared to those having 1 M and 2 M alleles. No differences in the HDL content concerning the major apolipoprotein and lipid constituents were observed between individuals carrying the PON1 L55L and those with the M55M polymorphism. Our results provide evidence that PON1 significantly contributes to the pool of HDL-PAF-AH activity in human plasma, and suggest that the low PAF-AH activity in HDL carrying the PON1 L alloenzyme may be an important factor contributing to the low efficiency of this HDL in protecting LDL against lipid peroxidation.

Activation of protein kinase C inhibits the secretion of platelet-activating factor acetylhydrolase by human decidual macrophages.

Background and Aims: Platelet activating factor (PAF), a potent phospholipid mediator, has been implicated in a number of reproductive processes through ovulation to parturition. To clarify the regulatory mechanism of PAF metabolism in the decidua, we have investigated the effect of activation of protein kinase C (PKC) on the secretion of PAF-acetylhydrolase (PAF-AH), a PAF-inactivating enzyme, by human decidual macrophages. Methods: Decidual macrophage populations were isolated from human decidua by using enzymic digestion, Ficoll-Paque centrifugation, or flow cytometric sorting. The cells were treated with a PKC activator (TPA), H-7, dibutyryl cyclic adenosine monophosphate (AMP), Bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, tetra (acetoxymethyl)-ester (BAPTA/AM) and/or nifedipine. The activity of PAF-AH secreted in the culture medium was assayed. Results: The PKC activator, TPA, inhibited the PAF-AH secretion by decidual cells in a dose-dependent manner. The TPA also decreased the enzyme secretion by flow cytometrically purified macrophages. The inhibitory effect of TPA was blocked by a PKC inhibitor, H-7. Protein kinase A (PKA) activation by dibutyryl cyclic AMP was without effect on the enzyme secretion. Calcium channel blockers, BAPTA/AM and nifedipine had no effect on the PAF-AH secretion. Conclusion: It is suggested that the TPA-induced inhibition of PAF-AH secretion may be mediated, in part, by a PKC-dependent signal transduction, and that activation of PKC may result in the increase in the local concentration of PAF in the decidua because of its inhibitory effect on the PAF-AH secretion by decidual macrophages. (Reprod Med Biol 2003; 2: 121-126).

Neonatal necrotizing enterocolitis: an overview.

Necrotizing enterocolitis represents a disease entity that remains quite challenging for neonatologists all around the world, in that its aetiology has yet to be revealed, but it is the cause of death for many premature infants each year, affecting up to 28% of very low birthweight infants. This is an attempt to improve the management of affected babies and stimulate more research concerning new diagnostic tools. Current trends in the field of (early) diagnosis, such as: (1) imaging techniques, e.g. contrast radiography, portal vein ultrasonography, magnetic resonance, radionuclide scanning; (2) gastrointestinal tonometry; (3) the detection of biochemical markers, cytokines, growth factors; and (4) the determination of the mean peak hydrogen: carbon dioxide ratio excreted in breath, are only some of those mentioned. Various novel preventive techniques are also presented, among which platelet-activating factor acetyl hydrolase activity enhancement, platelet-activating factor receptor antagonists and probiotics, such as Bifidobacterium infantis and Lactobacillus acidophilus, seem quite promising. Regarding treatment, the use of oxygenated perfluorocarbon has added to the limited alternatives available. These data along with other recent discoveries concerning the risk factors and pathogenesis of this disease create a full picture of the current opinion on this topic. Keeping in mind that the key to confronting such a devastating disorder as necrotizing enterocolitis is early diagnosis and prevention, both clinically applicable and experimental advances are presented with the hope of improving the survival rates of patients affected.

Platelet-activating factor acetylhydrolase is mainly associated with electronegative low-density lipoprotein subfraction.

Electronegative LDL [LDL(-)], a modified subfraction of LDL present in plasma, induces the release of interleukin-8 and monocyte chemotactic protein-1 from cultured endothelial cells. We demonstrate that platelet-activating factor acetylhydrolase (PAF-AH) is mainly associated with LDL(-). LDL(-) had 5-fold higher PAF-AH activity than the nonelectronegative LDL subfraction [LDL(+)] in both normolipemic and familial hypercholesterolemic subjects. Western blot analysis after SDS-PAGE confirmed these results, because a single band of 44 kDa corresponding to PAF-AH appeared in LDL(-) but not in LDL(+). Nondenaturing polyacrylamide gradient gel electrophoresis demonstrated that PAF-AH was bound to LDL(-) regardless of LDL size. In accordance with the above findings, nonesterified fatty acids, a cleavage product of PAF-AH, were increased in LDL(-) compared with LDL(+). The high PAF-AH activity observed in LDL(-) could be related to the proinflammatory activity of these lipoproteins toward cultured endothelial cells.

Serum platelet-activating factor acetylhydrolase (PAF-AH) activity in patients with hyperbilirubinemic hepatobiliary disease

Platelet-activating factor acetylhydrolase (PAF-AH) is an enzyme that catalyzes hydrolysis of PAF and is important for regulation of serum PAF concentration. Twenty-seven patients with hyperbililubinemic hepatobiliary diseases (eight patients with liver cirrhosis, five with acute hepatitis and 14 with obstructive cholestasis) were studied. Serum PAF-AH activity was elevated in hyperbilirubinemic condition associated with liver cirrhosis, obstructive cholestasis or acute hepatitis. There was a significant correlation of serum PAF-AH activity with serum cholesterol ( r=0.891, P=0.014 in liver cirrhosis, r=0.813, P=0.002 in obstructive cholestasis) or low density lipoprotein (LDL) cholesterol ( r=0.771, P=0.007 in obstructive cholestasis). Serum PAF-AH activity/cholesterol ratio and PAF-AH activity/LDL cholesterol ratio were elevated in the three types of hyperbilirubinemic liver disease. LDL cholesterol increased and PAF-AH/LDL cholesterol ratio decreased in acute hepatitis after remission. On the other hand, LDL cholesterol decreased and PAF-AH/LDL cholesterol ratio did not change after treatment in obstructive cholestasis. These findings suggest that, though serum LDL is a factor influencing serum PAF-AH activity in obstructive jaundice, other factors, i.e. reduced biliary PAF-AH excretion, may also influence serum PAF-AH activity in hyperbilirubinemic hepatobiliary diseases.

Platelet-activating factor promotes mucosal apoptosis via FasL-mediating caspase-9 active pathway in rat small intestine after ischemia-reperfusion.

Platelet activating factor (PAF) is a proinflammatory lipid mediator for inflammatory response. It is unclear whether PAF is involved in the very complex process of ischemia-reperfusion (I/R) induced mucosal apoptosis in small intestine. Intestinal I/R was induced in rats intestine by 60 min occlusion of the superior mesenteric artery, followed by a 60 min reperfusion. I/R induced mucosal apoptosis and PAF activity but inhibited PAF-acetylhydrolase activity. Increases in interleukin-6 (IL-6) and decreases in IL-10 were observed. Western blot analysis showed that I/R induced expressions of platelet endothelial cell adhesion molecule-1 (PECAM-1) and Fas and Fas ligand (FasL) proteins, cleaved Bid, and enhanced the release of cytochrome c from mitochondria to activate caspase-9. Pretreatment of PAF antagonist BN-52021 attenuated these changes, except the increase in Fas. The results showed that I/R-inhibited mucosal PAF-acetylhydrolase activity resulted in an increase of activated PAF. The activated PAF increased the mucosal IL-6 and PECAM-1, enhanced the expression of FasL but not Fas, and led to the cleavage of Bid and the release of cytochrome c from mitochondria to activate caspase-9. This finding suggests that PAF promotes mucosal apoptosis after I/R in the rat small intestine partly through FasL mediating caspase-9 active pathway.

Platelet-activating factor acetylhydrolase is increased in lung lavage fluid from patients with acute respiratory distress syndrome.

Platelet-activating factor (PAF) is a proinflammatory phospholipid that may contribute to inflammation in the acute respiratory distress syndrome (ARDS). PAF acetylhydrolase (PAF-AH) degrades PAF and regulates its biological activity. We characterized PAF-AH in bronchoalveolar lavage fluid from ARDS patients (n = 33, 22 survivors), patients at risk for ARDS (n = 6), and healthy controls (n = 6). Bronchoalveolar lavage was performed during acute (<96 hrs from onset), plateau (6 to 12 days), and late (> or = 14 days) phases of ARDS. Intubated patients with ARDS or a risk factor for ARDS. In ARDS, total bronchoalveolar lavage PAF-AH activity was markedly increased in the acute phase (87 +/- 89 mU/mL, n = 33) and then decreased in the plateau (23 +/- 14 mU/mL, n = 10) and late phases (19 +/- 14 mU/mL, n = 7) (p = .003). Total bronchoalveolar lavage PAF-AH activity during the acute phase of ARDS was also increased as compared with patients at risk for ARDS (16 +/- 13 mU/mL, n = 6) and healthy controls (3 +/- 3 mU/mL, n = 6) (p < .001). In contrast, plasma PAF-AH activities were the same in controls (3215 +/- 858 mU/mL, n = 6), in patients at risk for ARDS (3606 +/- 1607 mU/mL, n = 6), and during the acute phase of ARDS (3098 +/- 2395 mU/mL, n = 33) (p = .18). PAF-AH mRNA was present in alveolar macrophages in the acute phase of ARDS (five of six) and in at-risk patients (two of three) but not in healthy controls. PAF-AH activity is increased in bronchoalveolar lavage fluid from patients with ARDS. Likely sources include leakage of plasma PAF-AH into alveoli or release of PAF-AH from injured cells; however, the presence of PAF-AH mRNA in alveolar macrophages suggests that PAF-AH may be actively synthesized in the lungs of patients with ARDS. PAF-AH activity in the lungs of ARDS patients may regulate inflammation caused by PAF and related oxidized phospholipids generated in the inflammatory response.

4P-0972 Lipoprotein(a) inhibits PAF-induced activation of human platelets in a manner independent of the endogenous PAF-acetylhydrolase activity

4P-0972 Lipoprotein(a) inhibits PAF-induced activation of human platelets in a manner independent of the endogenous PAF-acetylhydrolase activity

Platelet-activating factor and Escherichia coliO157:H7 infections.

The role of platelet-activating factor (PAF), a phospholipid inflammatory mediator, in Escherichia coli O157:H7-associated hemolytic uremic syndrome (HUS) is unknown. PAF is synthesized by diverse cells and is degraded by PAF-acetylhydrolase (PAF-AH). Deficient PAF-AH activity results from a G-->T transversion at position 994 of exon 9. We examined children infected with E. coliO157:H7 to determine if PAF levels or the PAF-AH ( G994T) mutation reflects the risk of developing HUS. Plasma PAF concentrations were determined using chloroform/methanol extraction, thin layer chromatography purification, and scintillation proximity assay in 10 patients with uncomplicated infection (UI), 10 infected patients who subsequently developed HUS (pre-HUS), 5 HUS patients, and 8 healthy controls. The PAF-AH ( G994T) allele frequency was determined in 52 UI children, 15 with HUS, and 11 controls. Wilcoxon rank sum tests were performed to test differences in location (median) of pairs of groups. PAF levels were higher in the UI ( P=0.04) and pre-HUS ( P=0.01) groups than in healthy controls. No subject had the PAF-AH ( G994T) allele. Thus, elevated plasma PAF levels occur in E. coliO157:H7-infected children, even without HUS, but diminish when HUS develops. The PAF-AH ( G994T) allele does not contribute to the risk of developing HUS.

Effects of antihypertensive and hypolipidemic drugs on plasma and HDL-associated PAF-acetylhydrolase activity

Effects of antihypertensive and hypolipidemic drugs on plasma and HDL-associated PAF-acetylhydrolase activity

Reduction in the extent of atherosclerosis in apolipoprotein E-deficient mice induced by electroporation-mediated transfer of the human plasma platelet-activating factor acetylhydrolase gene into skeletal muscle

The effect of increasing the activity of plasma platelet-activating factor (PAF) acetylhydrolase (AH) (PAF-AH) on the progression of atherosclerosis in apolipoprotein E-deficient (apoE −/−) mice was examined by gene delivery to skeletal muscle. The expression vector pcDNA3.1 containing either human PAF-AH cDNA (pcDNA/PAF-AH) or green fluorescent protein cDNA (pcDNA/GFP) was introduced into the skeletal muscle of both hind legs of 6-week-old apoE −/− mice by electroporation. The activity of PAH-AH in plasma was significantly increased 4–16 weeks after electroporation of apoE −/− mice with 120 μg of pcDNA/PAF-AH; the maximal (2.5-fold) increase was apparent after 8 weeks. The mean thickness of the aortic wall, determined by 160 measurements in each mouse, was significantly reduced in apoE −/− mice 8–16 weeks after exposure to pcDNA/PAF-AH compared with that in corresponding control animals that received pcDNA/GFP. These results suggest that the electrotransfer of the plasma PAF-AH gene to skeletal muscle reduces the extent of atherosclerosis in apoE −/− mice.

Platelet-activating factor acetylhydrolase activity in cerebrospinal fluid of children with acute systemic or neurological illness.

Platelet-activating factor acetylhydrolase was analyzed in cerebrospinal fluid samples taken from children with a variety of neurological conditions (85 patients; mean age, 3.8 years) to determine it is involved in the defense mechanism against the toxic effect of inflammatory mediators in the central nervous system. A significant increase in cerebrospinal fluid activity was seen in the patients with meningitis and acute febrile illness in comparison with the control subjects. The activity was also significantly higher in the patients with meningitis than in the patients with inflammatory neurological diseases. In addition, the biochemical profile of cerebrospinal fluid platelet-activating factor acetylhydrolase was different from other known acetylhydrolases. These findings suggest that cerebrospinal fluid platelet-activating factor acetylhydrolase activity may be a sensitive marker of the host response to central nervous system infections.

Antioxidant properties of HDL in transgenic mice overexpressing human apolipoprotein A-II

Transgenic mice overexpressing human apolipoprotein A-II (huapoA-II) display high VLDL and low HDL levels. To evaluate the antioxidant potential of huapoA-II enriched HDL, we measured the activities of paraoxonase (PON) and platelet-activating factor acetylhydrolase (PAF-AH). Both activities decreased up to 43% in the serum of transgenic mice compared with controls, varied in parallel to HDL levels, but decreased less than HDL levels. The major part of PON and PAF-AH was associated with HDL, except in fed high huapoA-II-expressing mice, in which 20% of PAF-AH and 9% of PON activities were associated with VLDL. PON mRNA levels in the liver, its major site of synthesis, were similar in transgenic and control animals, indicating normal enzyme synthesis. In transgenic mice, the basal oxidation of lipoproteins was not increased, whereas their VLDL were more susceptible to oxidation than VLDL of controls. Interestingly, HDL of transgenic mice protected VLDL from oxidation more efficiently than HDL of controls. In conclusion, the decrease in both PON and PAF-AH activities in huapoA-II transgenic mice is best explained by their lower plasma HDL levels. However, the unchanged basal lipoprotein oxidation in transgenic mice suggests that huapoA-II-rich HDL may maintain adequate antioxidant potential.—Boisfer, E., D. Stengel, D. Pastier, P. M. Laplaud, N. Dousset, E. Ninio, and A-D. Kalopissis. Antioxidant properties of HDL in transgenic mice overexpressing human apolipoprotein A-II. J. Lipid Res. 2002. 43: 732–741.