Plasma platelet-activating factor acetylhydrolase activity is not associated with premature coronary atherosclerosis

Association of lipoprotein-associated phospholipase A2 mass with asymptomatic cerebral artery stenosis

Cerebral artery stenosis (CAS) is the most important causes of ischaemic stroke. Lipoprotein-associated phospholipase A2 (Lp-PLA2) plays 2 diverse roles in atherosclerosis (pro-inflammatory and anti-inflammatory), and the association between Lp-PLA2 mass and cardiovascular or cerebrovascular events is inconsistent among previous studies. A cross-sectional study including 2012 North Chinese adults aged ≥40 years was performed in 2010-2011 to investigate whether Lp-PLA2 mass is associated with asymptomatic cerebral artery stenosis (ACAS). Serum Lp-PLA2 mass was determined by enzyme-linked immunosorbent assay (ELISA). All participants underwent transcranial Doppler (TCD) and bilateral carotid duplex ultrasound to evaluate intracranial artery stenosis (ICAS) and extracranial arterial stenosis (ECAS). The median serum Lp-PLA2 mass of the participants was 140.74 ng/mL (interquartile range: 131.79-158.07 ng/mL). The adjusted odds ratio (OR) when comparing the 4th quartile to the 1st quartile of Lp-PLA2 was 1.98 (95% confidence interval (CI): 1.42-2.78), 1.79 (95% CI: 1.08-2.94) and 1.87 (95% CI: 1.28-2.73) for the occurrence of ACAS, asymptomatic ECAS and asymptomatic ICAS, respectively, after controlling for vascular risk factors. These independently significant associations remained statistically significant in the male or elderly subgroups, but not in females or middle-aged participants. Lp-PLA2 mass is positively correlated with subclinical atherosclerosis determined by ACAS, ICAS and ECAS in North Chinese, particularly in male and older participants, suggesting that serum Lp-PLA2 mass might be potential biomarker for the detection of ACAS in the adults.

Lipoprotein-associated phospholipase A2: a new marker to determine cardiovascular risk in hypercholesterolemic dyslipidaemic children

Background

Inflammation and hypercholesterolaemia contribute to atherosclerotic changes which can start in childhood. Children with hyperlipidaemias are at high risk for early coronary atherosclerosis. This study evaluates the relationship between lipoprotein-associated phospholipase A2 (Lp-PLA2), carotid intima-media thickness (CIMT) and flow-mediated dilatation in hypercholesterolaemic dyslipidaemic children.

Methods

We performed a case–control study consisting of 43 cases, aged 2 to 17 years, and 24 age-matched controls. Fasting blood samples were obtained from both groups for the measurement of a lipid profile (total cholesterol, LDL-C, HDL-C and triglycerides) and Lp-PLA2 in mass units. The latter was determined with a turbidimetric immunoassay method (PlacTest, DiaDexus Inc.) applied to an automated analyser. CIMT and flow-mediated dilatation measurements were undertaken by a paediatric cardiologist, using high-resolution B-mode ultrasonography.

Results

Total cholesterol, LDL-C and Lp-PLA2 concentrations were significantly higher in the cases than in the controls ( p < 0.001 for all three parameters). While CIMT values were also significantly higher in the patients compared to the controls ( P = 0.001), flow-mediated dilatation values were significantly lower ( P = 0.001). We found positive correlations between Lp-PLA2 and total cholesterol ( r = 0.41, P = 0.001), Lp-PLA2 and LDL-C ( r = 0.36, P = 0.004), Lp-PLA2 and CIMT ( r = 0.44, P = 0.019) and LDL-C and CIMT ( r = 0.41, P = 0.032); there were negative correlations between Lp-PLA2 and flow-mediated dilatation ( r = −0.15, P = 0.045), total cholesterol and flow-mediated dilatation ( r = −0.45, P = 0.017), LDL-C and flow-mediated dilatation ( r = −0.51, P = 0.006) and CIMT and flow-mediated dilatation ( r = −0.45, P = 0.016).

Conclusion

Lp-PLA2 concentrations are significantly elevated in hypercholesterolaemic dyslipidaemic children. Given the association of Lp-PLA2 with markers of atherosclerosis (total cholesterol, LDL-C, CIMT and flow-mediated dilatation), the finding of increased concentrations of Lp-PLA2 could be used to identify early atherosclerotic changes in hypercholesterolaemic dyslipidaemic children and may inform their clinical management.

Effects of Antihypertensive and Hypolipidemic Drugs on Plasma and High-Density Lipoprotein-Associated Platelet Activating Factor-Acetylhydrolase Activity

Background: Human plasma platelet activating factor acetylhydrolase (PAF-AH) is a phospholipase A2 primarily associated with low-density lipoprotein (LDL). PAF-AH activity has also been found on high-density lipoprotein (HDL). Most of the clinical studies that have investigated the plasma levels of PAF-AH activity in cardiovascular disease have involved patients who were under treatment with various drugs, such as antihypertensive or hypolipidemic agents. However, the influence of these drugs on the enzyme activity has not been adequately studied.

Material and Methods: We evaluated the effects of representative antihypertensive and hypolipidemic drugs on the total plasma, as well as on the HDL-associated PAF-AH activity, in 121 patients with essential hypertension and in 90 patients with dyslipidemias of type IIA or type IIB. Serum lipids and enzymatic activities were determined at baseline and after 3 months of treatment.

Results: The administration of lacidipine (4 mg, n = 21), valsartan (80 mg, n = 26), indapamide (2.5 mg, n = 20), benazepril (20 mg, n = 20), or atenolol (50 mg, n = 34) did not affect either the total plasma- or the HDL-associated PAF-AH activity. In contrast, treatment with fluvastatin (40 mg, n = 50) or ciprofibrate (100 mg, n = 40) reduced by 25% plasma PAF-AH activity ( P < .001) associated with a decrease in serum levels of total cholesterol and LDL-cholesterol ( P < .001). Furthermore, ciprofibrate induced an increase by 26% in HDL-associated PAF-AH activity ( P = .004) along with an increase in serum HDL-cholesterol levels ( P = .02).

Conclusions: Among all types of drugs studied, only those that significantly affect lipid metabolism, such as statins and fibrates, significantly influence PAF-AH activity in human plasma.

Predicting the Risk of Cardiovascular Disease

Although an atherogenic lipoprotein phenotype has been well recognized as an important predictor of cardiovascular disease, recent studies have demonstrated a number of additional lipid-related markers as emerging biomarkers to identify patients at risk for future coronary heart disease. Among them, lipoprotein-associated phospholipase A(2) (Lp-PLA(2)), seems to be a promising candidate that might be added to the clinical armamentarium for improved prediction of cardiovascular disease in the future. Of particular note, Lp-PLA(2) is the only enzyme that cleaves oxidized low-density lipoprotein (oxLDL) in the subendothelial space, with further generation of proinflammatory mediators such as lysophosphatidylcholine (LysoPC) and oxidized fatty acid (oxFA), thereby probably linking two important features of atherogenesis, namely oxidation of LDL and local inflammatory processes within the atherosclerotic plaque. This overview aims to summarize our current knowledge based on observations from recent experimental and clinical studies. Emphasis has been put on potential pathophysiological mechanisms of action and on the clinical relevance of Lp-PLA(2) in a wide variety of clinical settings, including apparently healthy individuals, patients with stable angina or acute coronary syndromes, after myocardial infarction, and with subclinical disease. Although a growing body of evidence from epidemiological and clinical studies suggests that Lp-PLA(2) may represent an independent and clinically relevant long-term risk marker for coronary heart disease and, probably, also for stroke, the role of this enzyme in the setting of the acute coronary syndrome remains to be established.

Variation of lipoprotein associated phospholipase A2 across demographic characteristics and cardiovascular risk factors: a systematic review of the literature

BACKGROUND

Lipoprotein association phospholipase A2 (Lp-PLA(2)), an enzyme which has been found in atherosclerotic plaque is currently under investigation in large Phase III clinical trials of vascular disease prevention. We assessed in a variety of different population settings variation of Lp-PLA(2) mass and activity across gender, ethnicity, diabetes, kidney disease and metabolic syndrome. We also assessed correlations with measures of circulating lipids, systemic inflammation and adiposity.

METHODS

Systematic review of studies measuring Lp-PLA(2) and at least one of the relevant characteristics in >50 participants.

RESULTS

We identified a total of 77 studies involving 102,499 participants meeting the inclusion criteria. Lp-PLA(2) mass and activity were consistently approximately 10% higher in males than females and 15% higher in Caucasians than African Americans or Hispanics. There were no clear associations of Lp-PLA(2) mass or activity with type II diabetes, markers of systemic inflammation (C-reactive protein, fibrinogen) or with body mass index. Correlations of Lp-PLA(2) mass or activity with low density lipoprotein cholesterol and apolipoprotein B were moderate and positive, whilst correlations with high density lipoprotein cholesterol were negative and moderate to weak. There was no clear differences in associations with any of the above characteristics in groups defined based upon prevalent cardiovascular disease or its risk factors.

CONCLUSIONS

Despite considerable variability in absolute levels of Lp-PLA(2) across studies, the variability of Lp-PLA(2) across gender, ethnicity, and levels of circulating lipids and markers of systemic inflammation are more consistent and appear not to vary importantly across categories defined by CVD or its risk factors.

A novel platelet-activating factor acetylhydrolase discovered in a metagenome from the earthworm-associated microbial community

Metagenomics is an emerging field for mining the bioresources for new biomolecules for potential application in biotechnology and biomedicine. In the present study, a novel acetylhydrolase (Est13) was detected during the function-based screening of a metagenomic library established from the DNA extracted from the cellulose-depleting microbial community set up with an earthworm cast. Analysis showed that Est13 exhibited some similarities with a human and parasite platelet-activating factor acetylhydrolase (PAF-AH) belonging to the SGNH hydrolase superfamily. Biochemical characterization of the purified recombinant enzyme using substrates common for hydrolases of this superfamily demonstrated that Est13 hydrolysed p-nitrophenyl acetate quite efficiently, with a k(cat) /K(M) value of 3209 mM(-1) s(-1). The Est13 showed highest activity at pH 8.0 and 40°C, conditions in which it is relatively stable compared with known PAF-AHs. In vitro functional analysis of the platelet-activating factor hydrolysis showed a dose- and time-dependent inhibition of platelet aggregation in the range of 2-4 µM, making this enzyme a potential candidate for biomedical applications.

Plasma lipoprotein-associated phospholipase A2 in patients with metabolic syndrome and carotid atherosclerosis

Background

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a recently identified and potentially useful plasma biomarker for cardiovascular and atherosclerotic diseases. However, the correlation between the Lp-PLA₂ activity and carotid atherosclerosis remains poorly investigated in patients with metabolic syndrome (MetS). The present study aimed to evaluate the potential role of Lp-PLA₂ as a comprehensive marker of metabolic syndrome in individuals with and without carotid atherosclerosis.

Methods

We documented 118 consecutive patients with MetS and 70 age- and sex-matched healthy subjects served as controls. The patients were further divided into two groups: 39 with carotid plaques and 79 without carotid plaques to elucidate the influence of Lp-PLA₂ on carotid atherosclerosis. The plasma Lp-PLA₂ activity was measured by using ELISA method and carotid intimal-media thickness (IMT) was performed by ultrasound in all participants.

Results

Lp-PLA₂ activity was significantly increased in MetS subgroups when compared with controls, and was higher in patients with carotid plaques than those without plaques (P < 0.05). Furthermore, we found that significant difference in Lp-PLA₂ was obtained between patients with three and four disorders of metabolic syndrome (P < 0.01). Age (β = 0.183, P = 0.029), LDL-cholesterol (β = 0.401, P = 0.000) and waist-hip ratio (β = 0.410, P = 0.000) emerged as significant and independent determinants of Lp-PLA₂ activity. Multiple stepwise regression analysis revealed that LDL-cholesterol (β = 0.309, P = 0.000), systolic blood pressure (β = 0.322, P = 0.002) and age (β = 0.235, P = 0.007) significantly correlated with max IMT, and Lp-PLA₂ was not an independent predictor for carotid IMT.

Conclusions

Lp-PLA₂ may be a modulating factor for carotid IMT via age and LDL-cholesterol, not independent predictor in the pathophysiological process of carotid atherosclerosis in patients with MetS.

Platelet activating factor-acetylhydrolase (PAF-AH) activity and HDL levels, but not PAF-AH gene polymorphisms, are associated with successful aging in Sicilian octogenarians

BACKGROUND AND AIMS

Aging is associated with an increased risk of developing atherosclerosis. Subjects over 80 years of age without cardiovascular disease provide a model to investigate the protective factors increasing their resistance to atherosclerotic disease. Platelet-activating factor acetylhydrolase (PAF-AH) is an enzyme associated with low density lipoprotein (LDL) and high density lipoprotein (HDL) inactivating platelet-activating factor (PAF) and preventing LDL oxidation by hydrolysis of oxidized phospholipids. The aim of the present study was to evaluate the contribution of the PAFAH gene Arg92His, Ile198Thr and Ala379Val polymorphisms to resistance toward developing cardiovascular events in healthy Sicilian octogenarians.

METHODS

Distribution of PAF-AH genotypes and activity, and biochemical parameters, were compared between 100 octogenarians and 200 healthy adults.

RESULTS

The individuals in the elderly group displayed significantly higher levels of HDL-C (p<0.001) and plasma (p<0.001) and HDL (p<0.001) PAF-AH activity. Analysis of PAFAH genotype distributions showed no significant differences between octogenarians and controls. No differences among PAF-AH genotypes with respect to plasma and HDL PAF-AH activity were found in either group.

CONCLUSIONS

Our results provide no evidence of a significant association between the PAF-AH gene Arg92His, Ile198Thr and Ala379Val polymorphisms and successful aging in Sicilians. They also emphasize that, in these subjects, aging is characterized by increased levels of PAF-AH activity and HDL-C.

Association between Lp-PLA2 and coronary artery disease: focus on its relationship with lipoproteins and markers of inflammation and hemostasis

Lipoprotein-associated phospholipase A2 (Lp-PLA2) generates pro-inflammatory molecules from oxidized LDL. We examined the association between Lp-PLA2 plasma concentrations and risk of stable coronary artery disease (CAD) in a large case-control study and further assessed the relationship between Lp-PLA2 and various lipid, inflammatory and hemostatic parameters. Lp-PLA2 concentrations were measured in 312 patients with CAD and in 479 age- and gender-matched blood donors. Various sensitive inflammatory and hemostatic markers and a complete lipoprotein profile were obtained. Lp-PLA2 concentrations were significantly higher in cases than in controls (296.1 ng/mL versus 266.0 ng/mL, p<0.0001). In multivariable logistic regression, the age- and gender-adjusted OR for the presence of CAD was 1.61 (95% CI, 1.07-2.44) if the top quartile of the Lp-PLA2 distribution was compared to the bottom quartile. Adjustment for traditional cardiovascular risk factors and statin use resulted in an OR of 2.04 (95% CI, 1.19-3.48). After additional controlling for vWF, the OR was slightly attenuated but still remained statistically significant (OR 1.91; 95% CI, 1.12-3.28). Thus, elevated Lp-PLA2 concentrations were associated with the presence of stable CAD, independent of various biochemical markers. Our results support the hypothesis that Lp-PLA2 may be a novel, independent risk marker for CAD.

Platelet-Activating Factor Acetylhydrolase Is Not Associated with Carotid Intima-Media Thickness in Hypercholesterolemic Sicilian Individuals

Background: Atherosclerosis is a complex, chronic disease that usually arises from the converging action of several pathogenic processes, including hypertension, hyperlipidemia, obesity, and the accumulation of oxidized LDL. Platelet-activating factor acetylhydrolase (PAF-AH) is a LDL- and HDL-bound enzyme that hydrolyzes and inactivates PAF and prevents LDL-cholesterol oxidation, thus delaying the onset of atherosclerotic disease.

Methods: We evaluated the relationship between variants of the PAF-AH gene polymorphisms Arg92His, Ile198Thr, and Ala379Val and the presence of carotid atherosclerosis in 190 hypercholesterolemic Sicilian individuals. Carotid artery intima-media wall thickness (IMT) was measured as an indicator of early atherosclerotic disease. The participants were classified according to having normal (≤1 mm) or abnormal (≥1 mm) IMT and were also investigated for physical characteristics and biochemical indices, including PAF-AH activity.

Results: PAF-AH activity and LDL concentrations were significantly correlated in hypercholesterolemic patients, but plasma PAF-AH activity and HDL were not significantly correlated in either IMT group. No significant differences were detected among the PAF-AH gene polymorphisms in both groups after correction for age, sex, body mass index, plasma glucose and lipid concentrations, PAF-AH activity, blood pressure, and smoking habits. The analysis of PAF-AH genotype distribution showed no significant differences in percentage of 92, 198, and 379 genotypes in both IMT groups.

Conclusion: Our data provided no evidence that PAF-AH polymorphisms influence PAF-AH activity and atherosclerosis in hypercholesterolemic Sicilian patients.

Inflammation, bioactive lipids and atherosclerosis: potential roles of a lipoprotein-associated phospholipase A2, platelet activating factor-acetylhydrolase

It is well established that inflammation is an integral feature of atherosclerosis and of the cardiovascular diseases which it underlies. Oxidative stress is also recognized as a key actor in atherogenesis, in which it is closely associated with the inflammatory response and bioactive lipid formation. Several bioactive lipids have been identified in the atherosclerotic plaque, including the potent inflammatory mediator platelet activating factor (PAF), PAF-like lipids, oxidised phospholipids (oxPL) and lysophosphatidylcholine (lyso-PC). Recent evidence has established a central role of two phospholipases (PL) in atherogenesis, the non-pancreatic Type II secretory phospholipase A(2) (sPLA(2)) and the lipoprotein-associated PLA(2)-alternatively termed as PAF-acetylhydrolase (PAF-AH). sPLA(2) is calcium-dependent and hydrolyses the sn-2 acyl group of glycerophospholipids of lipoproteins and cell membranes to produce lyso-PC and free fatty acids. It is also implicated in isoprostane production from oxPL. sPLA(2) is an acute phase reactant, which is upregulated by inflammatory cytokines and may represent a new independent risk factor for coronary heart disease. In contrast to sPLA(2), PAF-AH is calcium-independent and is specific for short acyl groups at the sn-2 position of the phospholipid substrate and with the exception of PAF, can equally hydrolyze oxPL to generate lyso-PC and oxidized fatty acids. Thus PAF-AH plays a key role in the degradation of proinflammatory oxPL and in the generation of lyso-PC and oxidized fatty acids. PAF-AH equally can also hydrolyze short-chain diacylglycerols, triacylglycerols, and acetylated alkanols, and displays a PLA(1) activity. Whereas sPLA(2) may represent a new independent risk factor for coronary artery disease, the potential relevance of PAF-AH to atherosclerosis remains the subject of debate, and recent results suggest that the potential role of the LDL-associated PAF-AH in atherogenesis may be distinct to that of the HDL-associated enzyme. This review is focused on the main structural and catalytic features of plasma PAF-AH, on the association of the enzyme with distinct lipoprotein particle subspecies, on its cellular sources, and finally on the potential significance of this lipoprotein-associated PLA(2) in cardiovascular disease.