HDL-associated Platelet-activating Factor Acetylhydrolase Research Articles

Association of the G994T and R92H genotypes of platelet-activating factor acetylhydrolase with risk of preeclampsia in Chinese women.

To investigate the relationship between platelet-activating factor acetylhydrolase (PAF-AH) gene (PLA2G7) G994T (V279F, rs76863441) and R92H (rs1805017) polymorphisms and risk of preeclampsia (PE) in Chinese women. This is a case-control study of 273 patients with PE and 530 healthy pregnant women. PLA2G7 genotypes were determined by polymerase chain reaction amplification and restriction analysis. Plasma PAF-AH, apolipoprotein (apo) B-containing lipoprotein-associated PAF-AH (apoB-PAF-AH), total high-density lipoprotein (HDL)-associated PAF-AH (H-PAF-AH), apoE-containing HDL-associated PAF-AH (apoE-H-PAF-AH) activities, and clinical, metabolic, and oxidative stress parameters were also analyzed. The frequencies of the GT+TT genotype (14.7 versus 9.2%, P=0.019) and T allele (7.5% versus 4.6%) of PLA2G7 G994T polymorphism were significantly higher in patients with PE than in the control subjects. The GT+TT genotypes remained a significant predictor for PE in a regression model including age, body mass index (BMI), plasma PAF-AH, H-PAF-AH, apoE-H-PAF-AH and apoB-PAF-AH activities as covariates (odds ratio (OR)=4.926, 95% confidence interval (CI): 1.707-14.219, P=0.003). The ratio of apoB-PAF-AH to H-PAF-AH activities was significantly higher, while serum triglyceride levels were lower in patients with the GT genotype compared with patients with the GG genotype (P<0.05). No significant differences were observed in the frequencies of the R92H genotype and allele between the PE and control groups. The PLA2G7 G994T, but not R92H, genetic polymorphism is associated with the risk of PE in Chinese women.

Ezetimibe Monotherapy Reduces Serum Levels of Platelet-Activating Factor Acetylhydrolase in Patients With Dyslipidemia.

BackgroundThe combination of ezetimibe with statin therapy reduced cardiovascular events compared to statin monotherapy in IMPROVEIT study, and ezetimibe monotherapy attenuated atherosclerosis in basic study. We previously showed ezetimibe monotherapy was especially effective for metabolic syndrome (MetS) patients. We investigated the effects of ezetimibe monotherapy for high-density lipoprotein cholesterol (HDL-chol) function and platelet-activating factor acetylhydrolase (PAF-AH) activity.MethodsForty-two patients who initially received ezetimibe (10 mg/day) without statin treatment for 16 weeks from January 2009 to August 2011 were enrolled. Patients were divided into MetS and non-MetS groups, and serum levels of lipids, PAF-AH, and HDL-chol efflux capacity (HDL-CEC) at baseline and after 16 weeks of treatment were investigated. Serum PAF-AH, HDL-associated PAF-AH (HDL-PAF-AH), and LDL-associated PAF-AH (LDL-PAF-AH) were measured.ResultsIn all patients, age, the percentages of males, and body mass index were 61.0 ± 8.8 years, 59.5% and 26.3 ± 3.4 kg/m2, respectively. Total cholesterol and low-density lipoprotein cholesterol (LDL-chol) were significantly decreased by ezetimibe monotherapy. Serum PAF-AH and LDL-PAF-AH were significantly decreased by ezetimibe monotherapy, whereas HDL-PAF-AH and HDL-CEC were not. There was no difference in the results of PAF-AH and HDL-CEC between MetS and non-MetS groups.ConclusionsEzetimibe monotherapy might prevent coronary heart disease (CHD) regardless of the presence of MetS, because PAF-AH was independent risk factor for CHD.

Hypertension in black patients

To investigate the relationship between platelet-activating factor acetylhydrolase (PAF-AH) gene (PLA2G7) G994T (V279F, rs76863441) and R92H (rs1805017) polymorphisms and risk of preeclampsia (PE) in Chinese women.This is a case-control study of 273 patients with PE and 530 healthy pregnant women.PLA2G7 genotypes were determined by polymerase chain reaction amplification and restriction analysis. Plasma PAF-AH, apolipoprotein (apo) B-containing lipoprotein-associated PAF-AH (apoB-PAF-AH), total high-density lipoprotein (HDL)-associated PAF-AH (H-PAF-AH), apoE-containing HDL-associated PAF-AH (apoE-H-PAF-AH) activities, and clinical, metabolic, and oxidative stress parameters were also analyzed.The frequencies of the GT + TT genotype (14.7 versus 9.2%, P = 0.019) and T allele (7.5% versus 4.6%) of PLA2G7 G994T polymorphism were significantly higher in patients with PE than in the control subjects. The GT + TT genotypes remained a significant predictor for PE in a regression model including age, body mass index (BMI), plasma PAF-AH, H-PAF-AH, apoE-H-PAF-AH and apoB-PAF-AH activities as covariates (odds ratio (OR) = 4.926, 95% confidence interval (CI): 1.707–14.219, P = 0.003). The ratio of apoB-PAF-AH to H-PAF-AH activities was significantly higher, while serum triglyceride levels were lower in patients with the GT genotype compared with patients with the GG genotype (P < 0.05). No significant differences were observed in the frequencies of the R92H genotype and allele between the PE and control groups.The PLA2G7 G994T, but not R92H, genetic polymorphism is associated with the risk of PE in Chinese women.

Association between ethnicity and obesity with high-density lipoprotein (HDL) function and subclass distribution.

BackgroundObesity and low high-density lipoprotein-cholesterol (HDL-C) levels are associated with cardiovascular risk. Surprisingly, despite a greater prevalence of obesity and lower HDL concentrations than white women, black South African women are relatively protected against ischaemic heart disease.MethodsWe investigated whether this apparent discrepancy may be related to different HDL function and subclass distribution in black and white, normal-weight and obese South African women (n = 40). HDL functionality was assessed by measuring paraoxonase (PON) activity, platelet activating factor acetylhydrolase (PAF-AH) activity, Oxygen Radical Absorbance Capacity (ORAC) and quantification of the expression of vascular cell adhesion molecule in endothelial cells. PON-1 and PAF-AH expression was determined in isolated HDL and serum using Western blotting. Levels of large, intermediate and small HDL subclasses were measured using the Lipoprint® system.ResultsPON activity was lower in white compared to black women (0.49 ± 0.09 U/L vs 0.78 ± 0.10 U/L, p < 0.05), regardless of PON-1 protein levels. Obese black women had lower PAF-AH activity (9.34 ± 1.15 U/L vs 13.89 ± 1.21 U/L, p <0.05) and HDL-associated PAF-AH expression compared to obese white women. Compared to normal-weight women, obese women had lower large HDL, greater intermediate and small HDL; an effect that was more pronounced in white women than black women. There were no differences in antioxidant capacity or anti-inflammatory function across groups.ConclusionsOur data show that both obesity and ethnicity are associated with differences in HDL functionality, while obesity was associated with decreases in large HDL subclass distribution. Measuring HDL functionality and subclass may, therefore, be important factors to consider when assessing cardiovascular risk.Electronic supplementary materialThe online version of this article (doi:10.1186/s12944-016-0257-9) contains supplementary material, which is available to authorized users.

HDL inhibits the effects of oxidized phospholipids on endothelial cell gene expression via multiple mechanisms

Oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phospholcholine (OxPAPC) and its component phospholipids accumulate in atherosclerotic lesions and regulate the expression of >1,000 genes, many proatherogenic, in human aortic endothelial cells (HAECs). In contrast, there is evidence in the literature that HDL protects the vasculature from inflammatory insult. We have previously shown that in HAECs, HDL attenuates the expression of several proatherogenic genes regulated by OxPAPC and 1-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphocholine. We now demonstrate that HDL reverses >50% of the OxPAPC transcriptional response. Genes reversed by HDL are enriched for inflammatory and vascular development pathways, while genes not affected by HDL are enriched for oxidative stress response pathways. The protective effect of HDL is partially mimicked by cholesterol repletion and treatment with apoA1 but does not require signaling through scavenger receptor class B type I. Furthermore, our data demonstrate that HDL protection requires direct interaction with OxPAPC. HDL-associated platelet-activating factor acetylhydrolase (PAF-AH) hydrolyzes short-chain bioactive phospholipids in OxPAPC; however, inhibiting PAF-AH activity does not prevent HDL protection. Our results are consistent with HDL sequestering specific bioactive lipids in OxPAPC, thereby preventing their regulation of select target genes. Overall, this work implicates HDL as a major regulator of OxPAPC action in endothelial cells via multiple mechanisms.

Pitavastatin Increases HDL Particles Functionally Preserved with Cholesterol Efflux Capacity and Antioxidative Actions in Dyslipidemic Patients

Although statins increase the plasma concentration of high-density lipoprotein cholesterol (HDL-C), it has not been elucidated whether the increased HDL particles possess normal antiatherosclerotic properties. Pitavastatin functions to increase the plasma HDL-C level and decrease the lowdensity lipoprotein cholesterol (LDL-C) level. In the present study, we sought to examine the qualitative changes in HDL during pitavastatin treatment. A total of 30 patients with dyslipidemia were treated with 2 mg of pitavastatin for four weeks. The cholesterol efflux capacity and activities of the antioxidative enzymes paraoxonase-1 (PON-1) and platelet-activating factor acetylhydrolase (PAF-AH) were evaluated using polyethethylene glycol-treated HDL fractions before and after pitavastatin treatment. Pitavastatin treatment decreased the serum LDL-C level by 39% and increased the serum HDL-C level by 9% (p＜0.05). In addition, pitavastatin increased the phospholipid content of HDL by 7.8% (p＜0.05). The pitavastatin-induced increase in the HDL-C level coincided with an increase in the cholesterol efflux capacity of the isolated HDL fraction of 8.6% (p＜0.05). The post-pitavastatin treatment activity of HDL-associated PON-1 (paraoxonase and arylesterase) was increased by 9% (p＜0.05) and 11% (p＜0.05), respectively, while the HDL-associated PAF-AH activity was not affected by pitavastatin. In addition to its LDL-C-lowering effects, pitavastatin elevates the HDL-C level and enhances the cholesterol efflux capacity and antioxidative properties of HDL. Pitavastatin therefore increases the amount of functional HDL without attenuating HDL quality.

Lipid Oxidation in Carriers of Lecithin:Cholesterol Acyltransferase Gene Mutations

Lecithin:cholesterol acyltransferase (LCAT) has been shown to play a role in the depletion of lipid oxidation products, but this has so far not been studied in humans. In this study, we investigated processes and parameters relevant to lipid oxidation in carriers of functional LCAT mutations. In 4 carriers of 2 mutant LCAT alleles, 63 heterozygotes, and 63 family controls, we measured activities of LCAT, paraoxonase 1, and platelet-activating factor-acetylhydrolase; levels of lysophosphatidylcholine molecular species, arachidonic and linoleic acids, and their oxidized derivatives; immunodetectable oxidized phospholipids on apolipoprotein (apo) B-containing and apo(a)-containing lipoproteins; IgM and IgG autoantibodies to malondialdehyde-low-density lipoprotein and IgG and IgM apoB-immune complexes; and the antioxidant capacity of high-density lipoprotein (HDL). In individuals with LCAT mutations, plasma LCAT activity, HDL cholesterol, apoA-I, arachidonic acid, and its oxidized derivatives, oxidized phospholipids on apo(a)-containing lipoproteins, HDL-associated platelet-activating factor-acetylhydrolase activity, and the antioxidative capacity of HDL were gene-dose-dependently decreased. Oxidized phospholipids on apoB-containing lipoproteins was increased in heterozygotes (17%; P<0.001) but not in carriers of 2 defective LCAT alleles. Carriers of LCAT mutations present with significant reductions in LCAT activity, HDL cholesterol, apoA-I, platelet-activating factor-acetylhydrolase activity, and antioxidative potential of HDL, but this is not associated with parameters of increased lipid peroxidation; we did not observe significant changes in the oxidation products of arachidonic acid and linoleic acid, immunoreactive oxidized phospholipids on apo(a)-containing lipoproteins, and IgM and IgG autoantibodies against malondialdehyde-low-density lipoprotein. These data indicate that plasma LCAT activity, HDL-associated platelet-activating factor-acetylhydrolase activity, and HDL cholesterol may not influence the levels of plasma lipid oxidation products.

Apolipoprotein E-containing HDL-associated platelet-activating factor acetylhydrolase activities and malondialdehyde concentrations in patients with PCOS

PAF and PAF-like oxidized phospholipids hydrolysed by platelet-activating factor (PAF) acetylhydrolase (AH) are potent lipid mediators involved in inflammation and atherosclerosis. Apolipoprotein (apo) E-containing high-density lipoprotein (HDL) has antioxidant, anti-inflammatory and anti-atherogenic properties. The study investigated apoE-containing HDL-associated PAF-AH (HDL-PAF-AH) and total (apoE-containing + apoE-poor) HDL-PAF-AH activities as well as malondialdehyde (MDA) concentration in 291 patients with polycystic ovary syndrome (PCOS) using the Rotterdam consensus criteria and 281 control women. Compared with the control women, patients with hyperandrogenism + oligo/anovulation + polycystic ovaries (PCO) or hyperandrogenism + PCO had lower total, apoE-containing and apoE-poor HDL-PAF-AH activities, while those with oligo/anovulation + PCO showed decreased total and apoE-poor HDL-PAF-AH activities. Other factors including insulin resistance and obesity in PCOS had the adverse effects associated with the HDL-PAF-AH activities. Serum MDA concentration was associated with PCOS, hyperandrogenism, insulin resistance and hypertriglyceridaemia in patients with PCOS. Decreased total and apoE-containing HDL-PAF-AH activities and increased serum MDA concentration may contribute to the pathogenesis of PCOS and potentially link to related complications responsible for oxidative stress and inflammation such as an increased risk for type 2 diabetes mellitus and/or future cardiovascular diseases in PCOS patients. Platelet-activating factor (PAF) acetylhydrolase (PAF-AH) hydrolyses and inactivates PAF and PAF-like oxidized phospholipids that are potent lipid mediators involved in inflammation and atherosclerosis. Apolipoprotein (apo) E-containing high-density lipoprotein (HDL) has antioxidant, anti-inflammatory and anti-atherogenic properties. The study investigated apoE-containing HDL-associated PAF-AH (HDL-PAF-AH) activities, total (apoE-containing + apoE-poor) HDL-PAF-AH activities as well as malondialdehyde (MDA) concentration in 291 patients with polycystic ovary syndrome (PCOS) using the Rotterdam consensus criteria and 281 control women. Our results reported for the first time, as far as is known, that the apoE-containing HDL has a relatively high PAF-AH activity and accounts for about 50% of total HDL-PAF-AH activity in both the patient and control groups. Compared with the control women, the patients with hyperandrogenism + oligo/anovulation + polycystic ovaries (PCO) or hyperandrogenism + PCO had lower total, apoE-containing and apoE-poor HDL-PAF-AH activities, while those with oligo/anovulation + PCO showed decreased total and apoE-poor HDL-PAF-AH activities. Other factors, including insulin resistance and obesity in PCOS, had adverse effects associated with the HDL-PAF-AH activities. Serum MDA concentration was associated with PCOS, hyperandrogenism, IR and hypertriglyceridaemia in patients with PCOS. Since HDL-PAF-AH activity has been consistently shown to play an anti-inflammatory and anti-atherogenic role, the decreased total and apoE-containing HDL-PAF-AH activities and increased serum MDA concentration may contribute to the pathogenesis of PCOS and potentially link to related complications responsible for oxidative stress and inflammation, such as an increased risk for type 2 diabetes mellitus and/or future cardiovascular diseases in PCOS patients.

HDL and immunomodulation: an emerging role of HDL against atherosclerosis

Changes in plasma lipoprotein profiles, particularly low levels of high-density lipoprotein (HDL) cholesterol, are associated with several inflammatory and immune diseases, including atherosclerosis and rheumatoid arthritis, implying the potential link between HDL and immunity. Accumulating evidence suggests that HDL possesses anti-inflammatory effects and has an important function in host defense as part of the innate immune system. In addition, HDL inhibits the ability of antigen-presenting cells (APCs) to stimulate T cells. It is subsequently discovered that HDL or HDL-associated platelet-activating factor-acetylhydrolase can restore the emigratory process of monocyte-derived dendritic cells and thus result in resolution of inflammatory reactions in atherosclerotic plaques. Lipid rafts in plasma membrane are the key structure responsible for the immunomodulation effects of HDL, the remarkable ability of HDL to regulate innate and adaptive immune responses extends our understanding of its atheroprotective role, and provides new therapeutic approaches to atherosclerosis and other inflammatory conditions.

HDL-associated factors provide additional prognostic information for coronary artery disease as determined by multi-detector row computed tomography

Background A significant relationship has been noted between the lipid profile and atherosclerotic coronary artery disease (CAD) using invasive coronary angiography. We tested the hypothesis that the severity of CAD as determined by a non-invasive method, multi-detector row computed tomography (MDCT), is also associated with lipidemic factors. Methods and results The subjects included 195 consecutive patients who underwent coronary angiography using MDCT because of suspected CAD. The number of significantly stenosed vessels (VD) as evaluated by MDCT, platelet-activating factor acetylhydrolase (PAF-AH), free cholesterol (FC), phospholipid (PL), remnant-like lipoprotein particle-cholesterol (RLP-C), apolipoprotein (apo)-B, apo-C3, apo-E, and highly-sensitive C-reactive protein were determined. The subjects were divided into diabetes mellitus (DM) and non-DM groups. The HDL-associated PAF-AH level in the DM group was significantly lower than that in the non-DM group. The VD determined by MDCT was significantly associated with hypertension, administration of angiotensin II type 1 receptor blocker, high-density lipoprotein cholesterol (HDL-C), HDL-associated (H)-HDL, H-PL, H-FC and RLP-C. Multivariate analysis revealed that VD determined by MDCT was most closely correlated with HDL-C. Conclusion Lower levels of HDL-C may be an indicator for and provide additional information regarding the severity of CAD compared with other lipidemic factors.

Ratio of LDL- to HDL-Associated Platelet-Activating Factor Acetylhydrolase may be a Marker of Inflammation in Patients With Paroxysmal Atrial Fibrillation

A higher plasma concentration of highly-sensitive C-reactive protein (hs-CRP) has been found in patients with atrial fibrillation (AF). In addition, low-density lipoprotein (LDL)-associated platelet-activating factor acetylhydrolase (L-PAF-AH) is associated with inflammation. Therefore, the association between AF and PAF-AH was examined. Eighty subjects who were not taking aspirin or statin were investigated, and classified into paroxysmal AF (n=41) and normal sinus rhythm (NSR, n=39) groups. The lipid profile was analyzed by capillary isotachophoresis (cITP), plasma hs-CRP, plasma PAF-AH, high-density lipoprotein (HDL)-associated (H-PAF-AH), and L-PAF-AH. Although there were no significant differences in total cholesterol, HDL, LDL, hs-CRP, or plasma PAF-AH between the 2 groups, L-PAF-AH and the L-PAF-AH/H-PAF-AH ratio in the paroxysmal AF group were both significantly higher than in the NSR group. Interestingly, the ratio of L-PAF-AH to H-PAF-AH positively correlated with the left atrial diameter in all subjects. Although there were no differences in plasma lipoprotein subfractions, as characterized by cITP, slow-migrating LDL positively correlated with L-PAF-AH in both groups. The distribution of PAF-AH was associated with paroxysmal AF and may be a marker of inflammation in patients with paroxysmal AF. Antiinflammatory and antioxidant therapy that targets these factors might be effective for preventing paroxysmal AF.

Alterations of Paraoxonase and Platelet-Activating Factor Acetylhydrolase Activities in Patients on Peritoneal Dialysis

The more atherogenic lipid profile seen in peritoneal dialysis (PD) patients cannot fully explain the increased incidence of atherosclerosis in this population. Oxidative modification of low-density lipoproteins (LDL) is considered to play a central role in the atherogenic process, whereas high-density lipoprotein (HDL) protects LDL from oxidation. On the other hand, it has been suggested that the LDL and HDL of PD patients are more resistant to oxidation than those of control subjects, while PD-HDL equally protects LDL from oxidation compared to control-HDL. Two HDL-associated enzymes have been shown to protect both LDL and HDL from oxidation: paraoxonase (PON1) and HDL-associated platelet-activating factor acetylhydrolase (HDL-PAF-AH). Furthermore, low PON1 activity and high total plasma PAF-AH concentration, which represents mainly the LDL-associated enzyme, have been shown to be independent risk factors for coronary artery events in the general population. However, there are limited data regarding possible alterations of these enzymes in PD patients. The aim of our study was to examine the possible alterations of PON1 and PAF-AH activities in patients undergoing PD. A cross-sectional study. A university medical center. 56 PD patients of Caucasian origin and 86 matched controls were studied. In all subjects, serum PON1 activity toward paraoxon (paraoxonase) and phenylacetate (arylesterase), as well as total serum and HDL-PAF-AH activities were measured; PON1 genetic polymorphisms known to influence PON1 activity (Q192R and M55L) were determined. The PD patients exhibited significantly increased serum PON1 (paraoxonase) and PON1 (arylesterase) activities compared to controls, regardless of the PON1 polymorphisms or the levels of HDL cholesterol. Additionally, PD patients had significantly elevated activities of total serum PAF-AH and HDL-PAF-AH, independently of the levels of LDL or HDL cholesterol. The ratio of HDL-PAF-AH/ total PAF-AH, which has recently been suggested to be a potential marker of atherogenicity, was decreased in these patients compared to controls. Moreover, no difference in the prevalence of PON1 polymorphisms between PD patients and controls was found. The elevated activities of PON1 and HDL-PAF-AH could explain the increased resistance of PD-HDL to oxidation; the higher activity of total PAF-AH and the decreased HDL-PAF-AH/ total PAF-AH ratio could contribute to the increased incidence of atherosclerosis in these patients.

Dyslipidemia Associated with Atherosclerotic Disease Systemically Alters Dendritic Cell Mobilization

High LDL and/or low HDL are risk factors for atherosclerosis and are also a common clinical feature in systemic lupus erythematosus, rheumatoid arthritis, and psoriasis. Here, we show that changes in lipid profiles that reflect atherosclerotic disease led to activation of skin murine dendritic cells (DCs) locally, promoted dermal inflammation, and induced lymph node hypertrophy. Paradoxically, DC migration to lymph nodes was impaired, suppressing immunologic priming. Impaired migration resulted from inhibitory signals generated by platelet-activating factor (PAF) or oxidized LDL that acts as a PAF mimetic. Normal DC migration and priming was restored by HDL or HDL-associated PAF acetylhydrolase (PAFAH), which mediates inactivation of PAF and oxidized LDL. Thus, atherosclerotic changes can sequester activated DCs in the periphery where they may aggravate local inflammation even as they poorly carry out functions that require their migration to lymph nodes. In this context, HDL and PAFAH maintain a normally functional DC compartment.

Inhibition of cholesteryl ester transfer protein activity by JTT-705 increases apolipoprotein E-containing high-density lipoprotein and favorably affects the function and enzyme composition of high-density lipoprotein in rabbits.

Inhibition of cholesteryl ester transfer protein (CETP) is an efficient way to increase high-density lipoprotein (HDL) levels in humans. We investigated the effects of the inhibition of CETP activity by a CETP inhibitor, JTT-705, on the function and composition of HDL particles. Japanese white rabbits were fed either normal rabbit chow LRC-4 (n=10) or a food admixture of LRC-4 and 0.75% JTT-705 (n=10) for 7 months. JTT-705 significantly inhibited CETP activities, increased HDL cholesterol (HDL-C) levels and the ratio of HDL2-C/HDL3-C, and decreased the fractional esterification rate of cholesterol in HDL, indicating preferentially increased large HDL particles. Treatment with JTT-705 increased all of the 3 charge-based HDL subfractions as determined by capillary isotachophoresis: fast-migrating, intermediate-migrating, and slow-migrating HDL. The percentage of slow HDL, ie, apolipoprotein E (apoE)-containing HDL and levels of apoE in HDL fraction, was also increased. JTT-705 treatment increased serum paraoxonase activity and HDL-associated platelet-activating factor acetylhydrolase activity, but decreased the plasma lysophosphatidylcholine concentration. Inhibition of CETP activity by JTT-705 not only increased the quantity of HDL, including HDL-C levels and charge-based HDL subfractions, but also favorably affected the size distribution of HDL subpopulations and the apolipoprotein and enzyme composition of HDL in rabbits.

Effects of intravenous apolipoprotein A-I/phosphatidylcholine discs on paraoxonase and platelet-activating factor acetylhydrolase in human plasma and tissue fluid

We have previously shown that intravenous apolipoprotein (apo) A-I/phosphatidylcholine (apo A-I/PC) discs increase plasma high-density lipoprotein (HDL) concentration in humans. We have now studied the associated changes in two enzymes, paraoxonase (PON) and platelet-activating factor acetylhydrolase (PAF-AH) that are carried in whole or in part by HDLs, and are thought to influence atherogenesis by hydrolyzing oxidized phospholipids in lipoproteins. Apo A-I/PC discs (40 mg/kg over 4 h) were infused into eight healthy males. Although plasma apo A-I and HDL cholesterol increased on average by 178 and 158%, respectively, plasma total PON and total PAF-AH concentrations did not rise. By the end of the infusion, HDL-associated PAF-AH had increased by 0.56 ± 0.14 μg/mL (mean ± S.D., P < 0.01), and nonHDL-associated PAF-AH had decreased by 0.84 ± 0.11 μg/mL ( P < 0.05). These changes were accompanied by an increase in the HDL-associated PAF-AH/apo A-I ratio from 0.19 to 0.35 ( P < 0.05), and by a decrease in the nonHDL-associated PAF-AH/apo B ratio from 2.1 to 1.4 ( P < 0.05). No changes in PON or PAF-AH concentrations were detected in prenodal lymph (tissue fluid), collected continuously from the leg. Our results show that the total concentrations of PON and PAF-AH in plasma are uninfluenced by plasma HDL concentration. PAF-AH transfers readily between HDLs and LDLs in vivo, and its distribution between them is determined partly by their relative concentrations and partly by HDL composition.

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.

Altered distribution of platelet-activating factor-acetylhydrolase activity between LDL and HDL as a function of the severity of hypercholesterolemia

Platelet-activating factor-acetylhydrolase (PAF-AH) is a lipoprotein-associated phospholipase A2 capable of hydrolyzing platelet-activating factor (PAF) and oxidatively modified phospholipids. We studied the plasma- and lipoprotein-associated PAF-AH activity in patients with primary hypercholesterolemia. Thirty-eight unrelated patients with heterozygous familial hypercholesterolemia (HeteroFH), five patients with homozygous FH (HomoFH), and 33 patients with primary non-FH hypercholesterolemia (NonFH) participated in the study. In all patient groups the plasma PAF-AH activity was significantly elevated compared with 33 normolipidemic controls, the HomoFH having the highest and the NonFH patients showing the lowest enzyme activity. Gradient ultracentrifugation studies showed that this increase is not only due to the elevation in the plasma LDL but also to the increase in the PAF-AH activity associated with each LDL subfraction, being more profound in the small-dense LDL-5. Unlike LDL, no difference in the HDL-associated PAF-AH activity was observed among all groups. Consequently, an altered distribution of enzyme activity among apolipoprotein B (apoB)- and apolipoprotein A-I (apoA-I)-containing lipoproteins is observed in hypercholesterolemic patients, resulting in a significant decrease in the ratio of the HDL-associated PAF-AH to the total plasma enzyme activity compared with controls. This reduction is proportional to the increase of the plasma LDL-cholesterol (LDL-C) levels and consequently to the severity of the hypercholesterolemia. Thus, the ratio of HDL-associated PAF-AH-total plasma enzyme activity may be useful as a potential marker of atherogenicity in subjects with primary hypercholesterolemia.—Tsimihodimos, V., S-A. P. Karabina, A. P. Tambaki, E. Bairaktari, G. Miltiadous, J. A. Goudevenos, M. A. Cariolou, M. J. Chapman, A. D. Tselepis, and M. Elisaf. Altered distribution of platelet-activating factor-acetylhydrolase activity between LDL and HDL as a function of the severity of hypercholesterolemia.

Effect of Overexpression of Human Apo A-I in C57BL/6 and C57BL/6 Apo E–Deficient Mice on 2 Lipoprotein-Associated Enzymes, Platelet-Activating Factor Acetylhydrolase and Paraoxonase

Various mechanisms may contribute to the antiatherogenic potential of apolipoprotein A-I (apo A-I) and high density lipoproteins (HDLs). Therefore, the effect of adenovirus-mediated human apo A-I gene transfer or human apo A-I transgenesis on platelet-activating factor acetylhydrolase (PAF-AH) and arylesterase/paraoxonase (PON1) was studied in C57BL/6 and C57BL/6 apo E(-/-) mice. Human apo A-I transgenesis in C57BL/6 mice resulted in a 4.2-fold (P<0.0001) increase of PAF-AH and a 1.7-fold (P=0.0012) increase of PON1 activity. The apo E deficiency was associated with a 1.6-fold (P=0.008) lower PAF-AH and a 2.0-fold (P=0.012) lower PON1 activity. Human apo A-I transgenesis in C57BL/6 apo E(-/-)mice increased PAF-AH and PON1 activity by 2.1-fold (P=0.01) and 2.5-fold (P=0.029), respectively. After adenovirus-mediated gene transfer of human apo A-I into C57BL/6 apo E(-/-)mice, a strong correlation between human apo A-I plasma levels and PAF-AH activity was observed at day 6 (r=0.92, P<0.0001). However, PON1 activity failed to increase, probably as a result of cytokine-mediated inhibition of PON 1 expression. In conclusion, this study indicates that overexpression of human apo A-I increases HDL-associated PAF-AH activity. PON1 activity was also increased in human apo A-I transgenic mice, but not after human apo A-I gene transfer, a result that was probably related to cytokine production induced in the liver by the adenoviral vectors. Increased levels of these HDL-associated enzymes may contribute to the anti-inflammatory and antioxidative potential of HDL and thereby to the protection conferred by HDL against atherothrombosis.

Increased activity of platelet-activating factor acetylhydrolase in low-density lipoprotein subfractions induces enhanced lysophosphatidylcholine production during oxidation in patients with heterozygous familial hypercholesterolaemia.

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.