Platelet-activating factor acetylhydrolase and transacetylase activities in human plasma low-density lipoprotein

2001 ◽  
Vol 357 (2) ◽  
pp. 457-464 ◽  
Author(s):  
Demokritos C. TSOUKATOS ◽  
Theodoros A. LIAPIKOS ◽  
Alexandros D. TSELEPIS ◽  
M. John CHAPMAN ◽  
Ewa NINIO
Keyword(s):  
Human Plasma ◽  
Low Density Lipoprotein ◽  
Platelet Activating Factor ◽  
Density Lipoprotein ◽  
Biologically Active ◽  
Low Density ◽  
Ether Linkage ◽  
Small Dense Ldl ◽  
Ldl Particles ◽  
Ldl Subfractions

In this study, we demonstrate the presence of a transacetylase activity in human plasma low-density lipoprotein (LDL) that transfers short-chain fatty acids from platelet-activating factor (PAF) and its close ether- and ester-linked analogues to ether/ester-linked lysophospholipids (lyso-PL). We show evidence that both PAF acetylhydrolase (PAF-AH) and transacetylase activities are inhibited to the same extent by serine esterase inhibitors, are resistant to heat treatment, and exhibit identical distributions in lipoprotein classes and in LDL subfractions. Additionally, the competitive inhibition of PAF-AH by lyso-PL, and the evidence that the recombinant PAF-AH also showed a similar transacetylase activity, suggest that PAF-AH is responsible for both activities. Using PAF as a donor molecule and lyso-PAF (1-O-alkyl-sn-glycero-3-phosphocholine) as an acceptor, the transacetylase activity showed typical allosteric kinetics, due to the positive co-operativity of the substrates, with apparent Vmax = 19.6±3.4nmol/min per mg of protein, apparent h = 2.0±0.3 and apparent [S]0.5 = 9.4±2.3μM at saturation for the concentration of lyso-PAF. The substrate specificity of the donor molecules was decreased by increasing the chain length of the acyl moiety in the sn-2 position of the glycerol. The ether linkage in the sn-1 position of the substrate was 30% more effective than the ester bond; cholesteryl acetate was inactive as an acetyl donor. The two acceptors tested, lyso-PAF and the ester-linked lyso-PC (1-acyl-sn-glycero-3-phosphocholine), showed similar specificity. Addition of exogenous lyso-PAF induced the transient formation of PAF-like aggregating activity predominately in small dense LDL subfractions upon oxidation. We conclude that PAF-AH possesses both transacetylase and acetylhydrolase activities which remove PAF and its ether-linked analogues from LDL particles upon LDL oxidation. However, in atherogenic small dense LDL-5 particles, the transacetylase activity may acetylate extracellular lyso-PAF into biologically active PAF.

scholarly journals Reduced β-strand content in apoprotein B-100 in smaller and denser low-density lipoprotein subclasses as probed by Fourier-transform infrared spectroscopy

1997 ◽  
Vol 322 (3) ◽  
pp. 765-769 ◽  
Author(s):  
Fabio TANFANI ◽  
Tiziana GALEAZZI ◽  
Giovanna CURATOLA ◽  
Enrico BERTOLI ◽  
Gianna FERRETTI
Keyword(s):  
Fourier Transform ◽  
Secondary Structure ◽  
Apolipoprotein B ◽  
Gradient Centrifugation ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Lipoprotein Subclasses ◽  
Ldl Particles ◽  
Ldl Subfractions

The secondary structure of apolipoprotein B-100 in low-density lipoprotein (LDL) subfractions was analysed by Fourier-transform IR spectroscopy. LDLs were isolated in three density ranges by gradient centrifugation of human plasma from healthy volunteers. The spectra revealed differences in the lipid content and composition of the three LDL fractions. The secondary structure of apolipoprotein B-100 was the same in the two fractions corresponding to the large less-dense LDL particles, whereas a lower content of β-strands was found in the third fraction corresponding to the smaller denser LDL particles. Analysis of the spectroscopic data suggests that, in the same set of LDL subfractions, the particle size is probably the cause of the observed differences in apolipoprotein B-100 secondary structure.

scholarly journals Platelet-activating factor acetylhydrolase and transacetylase activities in human plasma low-density lipoprotein

2001 ◽  
Vol 357 (2) ◽  
pp. 457 ◽  
Author(s):  
Demokritos C. TSOUKATOS ◽  
Theodoros A. LIAPIKOS ◽  
Alexandros D. TSELEPIS ◽  
M. John CHAPMAN ◽  
Ewa NINIO
Keyword(s):  
Human Plasma ◽  
Low Density Lipoprotein ◽  
Platelet Activating Factor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Platelet Activating Factor Acetylhydrolase

scholarly journals Oxidative Modification of Lipoproteins: A Potential Role of Oxidized Small dense LDL in Enhanced Atherogenicity

2021 ◽  
pp. 118-140
Author(s):  
Mohammed Alsaweed
Keyword(s):  
Arterial Wall ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Predictive Marker ◽  
Oxidative Modification ◽  
Cholesterol Homeostasis ◽  
Low Density ◽  
Small Dense Ldl ◽  
Ldl Particles ◽  
Apoprotein B

Atherosclerosis (AS) is a multifaceted inflammatory syndrome of the arterial wall to which number of mediators have been implicated in lesion progression. Triglyceride (TG)-rich lipoproteins consist of the large diversity of lipoprotein particles that fluctuate in density, size, and apolipoprotein composition. Two foremost phenotypes, on basis of size, chemical configuration, and density, of low-density-lipoprotein (LDL) have been recognized i.e., pattern A, having LDL diameter greater than 25.5nm (large buoyant LDL or lb-LDL) and pattern B, having LDL diameter less than or equal to 25.5nm (small-dense LDL or sd-LDL). Small-dense low-density-lipoprotein (sd-LDL) particles are produced by potential intravascular hydrolysis of TG-rich VLDL particles via lipoprotein lipases (LPLs), hepatic lipases (HLs) and cholesterol ester transfer protein (CETP). sd-LDL is more atherogenic due to its smaller size, increased penetration into the arterial wall, extended plasma half-life, lesser binding affinity for LDL receptors (LDL-R) as well as lower resistance to oxidative stress when equated with lb-LDL. The higher atherogenic potential of sd-LDL is due to its enhanced susceptibility to oxidation, owing to high polyunsaturated fatty acids (PUFA), low cholesterol and Apoprotein B (ApoB) content. An enhanced understanding of sd-LDL metabolism at the molecular level, transport and clearance may result in the development of sd-LDL as an independent predictive marker for AS events and may be used to maintain cholesterol homeostasis and prevent the succession of AS.

scholarly journals The effects of fat consumption on low-density lipoprotein particle size in healthy individuals: a narrative review

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Erik Froyen
Keyword(s):  
Fatty Acids ◽  
Particle Size ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Healthy Individuals ◽  
Cvd Risk ◽  
Small Dense Ldl ◽  
Ldl Particles ◽  
Fat Consumption

AbstractCardiovascular disease (CVD) is the number one contributor to death in the United States and worldwide. A risk factor for CVD is high serum low-density lipoprotein cholesterol (LDL-C) concentrations; however, LDL particles exist in a variety of sizes that may differentially affect the progression of CVD. The small, dense LDL particles, compared to the large, buoyant LDL subclass, are considered to be more atherogenic. It has been suggested that replacing saturated fatty acids with monounsaturated and polyunsaturated fatty acids decreases the risk for CVD. However, certain studies are not in agreement with this recommendation, as saturated fatty acid intake did not increase the risk for CVD, cardiovascular events, and/or mortality. Furthermore, consumption of saturated fat has been demonstrated to increase large, buoyant LDL particles, which may explain, in part, for the differing outcomes regarding fat consumption on CVD risk. Therefore, the objective was to review intervention trials that explored the effects of fat consumption on LDL particle size in healthy individuals. PubMed and Web of Science were utilized during the search process for journal articles. The results of this review provided evidence that fat consumption increases large, buoyant LDL and/or decreases small, dense LDL particles, and therefore, influences CVD risk.

Triacylglycerol-rich lipoproteins and the generation of small, dense low-density lipoprotein

2003 ◽  
Vol 31 (5) ◽  
pp. 1066-1069 ◽  
Author(s):  
C.J. Packard
Keyword(s):  
Residence Time ◽  
Hepatic Lipase ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Low Density ◽  
Predisposing Factor ◽  
Small Dense Ldl ◽  
Lipoprotein Class ◽  
Ldl Particles ◽  
Clinical Benefits

LDL (low-density lipoprotein) is the major carrier of cholesterol in human plasma, and as such is intimately involved in the process of atherosclerosis. The lipoprotein class comprises a number of distinct subfractions, and is commonly divided into large, intermediate and small sized particles. Small, dense LDLs are held to be particularly atherogenic, since these particles are retained preferentially by the artery wall, are readily oxidized and carry an enzyme believed to have an important role in atherosclerosis, i.e. lipoprotein-associated phospholipase A2. Generation of small, dense LDL occurs by intravascular lipoprotein remodelling as a result of disturbances such as Type II diabetes, metabolic syndrome, renal disease and pre-eclampsia. The key predisposing factor is the development of hypertriglyceridaemia, in particular elevation in the plasma concentration of large, triacylglycerol-rich VLDL (very-low-density lipoprotein). This leads to the formation of slowly metabolized LDL particles (5-day residence time), which are subject to exchange processes that remove cholesteryl ester from the particle core and replace it with triacylglycerol. LDL, so altered, is a potential substrate for hepatic lipase; if the activity of the enzyme is high enough, lipolysis will generate smaller, denser particles. Correction of the dyslipidaemia associated with small, dense LDL is possible using fibrates and statins, and this may contribute to the clinical benefits seen with these drugs. Fibrates act to lower plasma triacylglycerol (VLDL) levels, and so correct the underlying metabolic disturbance. Statins remove VLDL particles via receptor-mediated pathways and reduce the residence time (and hence limit the potential for remodelling) of LDL in the circulation.

scholarly journals Lipoprotein-associated phospholipase A2, platelet-activating factor acetylhydrolase, generates two bioactive products during the oxidation of low-density lipoprotein: use of a novel inhibitor

1999 ◽  
Vol 338 (2) ◽  
pp. 479-487 ◽  
Author(s):  
Colin H. MACPHEE ◽  
Kitty E. MOORES ◽  
Helen F. BOYD ◽  
Dash DHANAK ◽  
Robert J. IFE ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Phospholipase A2 ◽  
Low Density Lipoprotein ◽  
Platelet Activating Factor ◽  
Density Lipoprotein ◽  
Oxidative Modification ◽  
Biologically Active ◽  
Lipid Hydroperoxides ◽  
Low Density ◽  
Platelet Activating Factor Acetylhydrolase

A novel and potent azetidinone inhibitor of the lipoprotein-associated phospholipase A2 (Lp-PLA2), i.e. platelet-activating factor acetylhydrolase, is described for the first time. This inhibitor, SB-222657 (Ki = 40±3 nM, kobs/[I] = 6.6×105 M-1·s-1), is inactive against paraoxonase, is a poor inhibitor of lecithin:cholesterol acyltransferase and has been used to investigate the role of Lp-PLA2 in the oxidative modification of lipoproteins. Although pretreatment with SB-222657 did not affect the kinetics of low-density lipoprotein (LDL) oxidation by Cu2+ or an azo free-radical generator as determined by assay of lipid hydroperoxides (LOOHs), conjugated dienes and thiobarbituric acid-reacting substances, in both cases it inhibited the elevation in lysophosphatidylcholine content. Moreover, the significantly increased monocyte chemoattractant activity found in a non-esterified fatty acid fraction from LDL oxidized by Cu2+ was also prevented by pretreatment with SB-222657, with an IC50 value of 5.0±0.4 nM. The less potent diastereoisomer of SB-222657, SB-223777 (Ki = 6.3±0.5 µM, kobs/[I] = 1.6×104 M-1·s-1), was found to be significantly less active in both assays. Thus, in addition to generating lysophosphatidylcholine, a known biologically active lipid, these results demonstrate that Lp-PLA2 is capable of generating oxidized non-esterified fatty acid moieties that are also bioactive. These findings are consistent with our proposal that Lp-PLA2 has a predominantly pro-inflammatory role in atherogenesis. Finally, similar studies have demonstrated that a different situation exists during the oxidation of high-density lipoprotein, with enzyme(s) other than Lp-PLA2 apparently being responsible for generating lysophosphatidylcholine.

Intralysosomal Accumulation of Colloidal Gold-Low Density Lipoprotein Conjugates in Chloroquine-Treated Fibroblasts

1985 ◽  
Vol 43 ◽  
pp. 546-547 ◽  
Author(s):  
Dean A. Handley ◽  
Cynthia M. Arbeeny ◽  
Larry D. Witte
Keyword(s):  
Colloidal Gold ◽  
Cultured Cells ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Coated Vesicle ◽  
Low Density ◽  
Cholesterol Esters ◽  
Cultured Fibroblasts ◽  
Surface Receptors ◽  
Ldl Particles

Low density lipoproteins (LDL) are the major cholesterol carrying particles in the blood. Using cultured cells, it has been shown that LDL particles interact with specific surface receptors and are internalized via a coated pit-coated vesicle pathway for lysosomal catabolism. This (Pathway has been visualized using LDL labeled to ferritin or colloidal gold. It is now recognized that certain lysomotropic agents, such as chloroquine, inhibit lysosomal enzymes that degrade protein and cholesterol esters. By interrupting cholesterol ester hydrolysis, chloroquine treatment results in lysosomal accumulation of cholesterol esters from internalized LDL. Using LDL conjugated to colloidal gold, we have examined the ultrastructural effects of chloroquine on lipoprotein uptake by normal cultured fibroblasts.

Studies on the Thromboplastic Effect of Human Plasma Lipoproteins

1976 ◽  
Vol 35 (01) ◽  
pp. 178-185 ◽  
Author(s):  
Helena Sandberg ◽  
Lars-Olov Andersson
Keyword(s):  
High Density Lipoprotein ◽  
Human Plasma ◽  
Platelet Rich Plasma ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Very Low Density Lipoprotein ◽  
Low Density ◽  
Free Plasma ◽  
Good Agreement

SummaryHuman plasma lipoprotein fractions were prepared by flotation in the ultracentrifuge. Addition of these fractions to platelet-rich, platelet-poor and platelet-free plasma affected the partial thromboplastin and Stypven clotting times to various degrees. Addition of high density lipoprotein (HDL) to platelet-poor and platelet-free plasma shortened both the partial thromboplastin and the Stypven time, whereas addition of low density lipoprotein and very low density lipoprotein (LDL + VLDL) fractions only shortened the Stypven time. The additions had little or no effect in platelet-rich plasma.Experiments involving the addition of anti-HDL antibodies to plasmas with different platelet contents and measuring of clotting times produced results that were in good agreement with those noted when lipoprotein was added. The relation between structure and the clot-promoting activity of various phospholipid components is discussed.

scholarly journals Aggregation Susceptibility of Low-Density Lipoproteins—A Novel Modifiable Biomarker of Cardiovascular Risk

2021 ◽  
Vol 10 (8) ◽  
pp. 1769
Author(s):  
Katariina Öörni ◽  
Petri T. Kovanen
Keyword(s):  
Ex Vivo ◽  
Low Density Lipoprotein ◽  
Density Lipoprotein ◽  
Atherosclerotic Cardiovascular Disease ◽  
Low Density ◽  
Cholesterol Crystals ◽  
Ldl Particles ◽  
Arterial Intima ◽  
Matrix Bound ◽  
Atherosclerotic Cardiovascular Diseases

Circulating low-density lipoprotein (LDL) particles enter the arterial intima where they bind to the extracellular matrix and become modified by lipases, proteases, and oxidizing enzymes and agents. The modified LDL particles aggregate and fuse into larger matrix-bound lipid droplets and, upon generation of unesterified cholesterol, cholesterol crystals are also formed. Uptake of the aggregated/fused particles and cholesterol crystals by macrophages and smooth muscle cells induces their inflammatory activation and conversion into foam cells. In this review, we summarize the causes and consequences of LDL aggregation and describe the development and applications of an assay capable of determining the susceptibility of isolated LDL particles to aggregate when exposed to human recombinant sphingomyelinase enzyme ex vivo. Significant person-to-person differences in the aggregation susceptibility of LDL particles were observed, and such individual differences largely depended on particle lipid composition. The presence of aggregation-prone LDL in the circulation predicted future cardiovascular events in patients with atherosclerotic cardiovascular disease. We also discuss means capable of reducing LDL particles’ aggregation susceptibility that could potentially inhibit LDL aggregation in the arterial wall. Whether reductions in LDL aggregation susceptibility are associated with attenuated atherogenesis and a reduced risk of atherosclerotic cardiovascular diseases remains to be studied.

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