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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2006;26:1586.)
© 2006 American Heart Association, Inc.

Atherosclerosis and Lipoproteins

Lipoprotein-Associated Phospholipase A₂ Predicts Future Cardiovascular Events in Patients With Coronary Heart Disease Independently of Traditional Risk Factors, Markers of Inflammation, Renal Function, and Hemodynamic Stress

Wolfgang Koenig; Dorothee Twardella; Hermann Brenner; Dietrich Rothenbacher

From the Department of Internal Medicine II-Cardiology (W.K.), University of Ulm Medical Center, Ulm, Germany; Department of Epidemiology (D.T., H.B., D.R.), German Centre for Research on Ageing at the University of Heidelberg, Heidelberg, Germany.

Correspondence to Wolfgang Koenig, MD, FRCP, FESC, FACC, Department of Internal Medicine II–Cardiology, University of Ulm Medical Center, Robert-Koch Str. 8, D-89081 Ulm, Germany. E-mail wolfgang.koenig{at}medizin.uni-ulm.de

	Abstract

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Objectives— We sought to evaluate whether lipoprotein-associated phospholipase A₂ (Lp-PLA₂), an emerging marker of cardiovascular risk, is associated with prognosis in patients with coronary heart disease (CHD).

Methods and Results— Plasma concentrations and activity of Lp-PLA₂ were determined in 1051 patients aged 30 to 70 years with CHD who were followed for &4 years. A Cox proportional hazards model was used to determine the prognostic value of Lp-PLA₂ after adjustment for various covariates, including markers of inflammation, renal function, and hemodynamic stress. In multivariable analyses, Lp-PLA₂ mass and activity were strongly associated with cardiovascular events after controlling for traditional risk factors, severity of CHD, statin treatment, cystatin C, and N-terminal proBNP. The hazard ratio (HR) for recurrent events was 2.65 (95% confidence interval [CI], 1.47 to 4.76) for the top tertile of Lp-PLA₂ mass compared with the bottom tertile and 2.40 (95% CI, 1.35 to 4.29) for Lp-PLA₂ activity. After additional adjustment for low-density lipoprotein (LDL), the HRs were only moderately attenuated (mass: 2.09; 95% CI, 1.10 to 3.96; activity: 1.81; 95% CI, 0.94 to 3.49, respectively), but the latter was no longer statistically significant.

Conclusions— Increased concentrations of Lp-PLA₂ predict future cardiovascular events in patients with manifest CHD independent of a variety of potential risk factors including markers of inflammation, renal function, and hemodynamic stress.

We found that lipoprotein-associated phospholipase A₂ (Lp-PLA₂) strongly predicts secondary cardiovascular events in patients with manifest coronary heart disease (CHD). In multivariable analysis, even including markers of inflammation, renal function, and hemodynamic stress, patients in the top tertile of the Lp-PLA₂ mass and activity distribution showed &2-fold increased risk compared with those in the bottom tertile.

Key Words: cohort study • coronary heart disease • inflammation • lipoprotein-associated phospholipase A₂ pathomechanism • prognosis

	Introduction

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Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) is a calcium-independent member of the phospholipase A₂ family.^1,2 It is produced mainly by monocytes, macrophages, T-lymphocytes, and mast and liver cells.^3–5 Lp-PLA₂ activity occurs in association with macrophages and has been found to be upregulated in atherosclerotic lesions, especially in complex plaque,⁶ as well as in the fibrous cap of coronary lesions prone to rupture.⁷ In the bloodstream, two-thirds of the Lp-PLA₂ plasma isoform circulate primarily bound to low-density lipoprotein (LDL), the other one-third is bounded to between high-density lipoprotein (HDL) and very-low-density lipoprotein.^8,9

LDL provides a circulating reservoir, in which Lp-PLA₂ remains inactive until LDL undergoes oxidative modification. After LDL oxidation within the arterial wall, a short acyl group at the sn-2 position of phospholipids becomes susceptible to the hydrolytic action of Lp-PLA₂ that cleaves an oxidized phosphatidylcholine component of the lipoprotein particle, generating 2 potent pro-inflammatory and pro-atherogenic mediators, namely lysophosphatidylcholine (LysoPC) and oxidized fatty acid (oxFA).¹⁰ Of particular note, Lp-PLA₂ acts only on oxidatively modified LDLs (oxLDL), and hydrolysis of oxLDL can be performed solely by Lp-PLA₂.^1,10 Pro-inflammatory actions of LysoPC, as well as those of oxFA, trigger a cascade of events, which might directly promote atherogenesis. LysoPC is a potent chemoattractant for T cells and monocytes, promotes endothelial cell dysfunction, stimulates macrophage proliferation, and induces apoptosis in smooth muscle cells and macrophages.^1,11,12

Thus, Lp-PLA₂ may represent an important "missing link" between the oxidative modification of LDL in the intimal layer of the arterial wall and local inflammatory processes within the atherosclerotic plaque that may be specific for atherosclerosis. Experimental studies in Watanabe heritable hyperlipidemic rabbits have shown that inhibition of Lp-PLA₂ leads to the reduction of atherosclerotic lesion formation.¹ The pro-atherogenic role of this enzyme was also implicated by observations from in vitro studies that suggested Lp-PLA₂ as a novel therapeutic target. Pyromidones, being noncovalent Lp-PLA₂ inhibitors, prevented the production of LysoPC and subsequent monocyte chemotaxis in vitro.^13,14 Further in vivo studies revealed a 95% inhibition of Lp-PLA₂ in atherosclerotic plaque from Watanabe heritable hyperlipidemic rabbits, observed 2 hours after dosing (30 mg/kg) of SB-480848,¹⁵ thereby identifying this compound as a very potent Lp-PLA₂ inhibitor with a suitable profile for evaluation in humans. Results from a multi-center trial¹⁶ showed a dose-dependent inhibition of Lp-PLA₂ plasma activity by 52% and 81% compared with placebo after administration of 40 mg and 80 mg of SB-480848, respectively.

To date, 4 large prospective studies^17–20 in initially healthy subjects support the notion that Lp-PLA₂ may be considered a new and independent cardiovascular biomarker. However, to our knowledge, only 1 study in patients with manifest coronary heart disease (CHD) has investigated the association between Lp-PLA₂ and future adverse cardiovascular events,²¹ and no study so far has determined whether Lp-PLA₂ mass or activity are more important.

Thus, because it is presently unclear to what extent Lp-PLA₂ mass and activity carry the same prognostic information, we sought to investigate simultaneously the value of both parameters for the prediction of future cardiovascular events in a large cohort of patients with manifest CHD. Furthermore, we wanted to compare its prognostic value with that of other emerging risk markers, like C-reactive protein (CRP), cystatin C as an indicator of renal function, and N-terminal-pro brain natriuretic peptide (NT-proBNP) as a measure of hemodynamic stress.

	Materials and Methods

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Study Population
All patients with CHD (International Classification of Diseases, 9th Revision codes 410 to 414) aged 30 to 70 years and participating in an in-hospital rehabilitation program between January 1999 and May 2000 in 2 cooperating clinics (Schwabenland-Klinik, Isny and Klinik im Südpark, Bad Nauheim, Germany) were enrolled in the study (initial response 58%). In Germany all patients, after acute coronary syndrome or coronary artery revascularization, are offered a comprehensive in-hospital rehabilitation program after discharge from the acute care hospital. The aim of this 3-week program is the reduction of cardiovascular risk factors, improvement of health related quality of life, and the preservation of the ability to work (the latter only if a subject was still at work at the onset of disease, otherwise the prevention of nursing care). This in-hospital rehabilitation program usually starts &3 weeks after the acute event or coronary artery revascularization. In the current study, only patients who were admitted within 3 months after the acute event or coronary artery revascularization have been included.

All subjects gave written informed consent. The study was approved by the Ethics Boards of the Universities of Ulm and Heidelberg and of the Physicians’ chamber of the States of Baden-Wuerttemberg and Hessen (Germany).

Data Collection
At the beginning of the in-hospital rehabilitation program all subjects filled out a standardized questionnaire containing sociodemographic information and medical history. In addition, information was taken from the patients’ hospital charts. In all patients active follow-up was conducted 1, 3, and 4.5 years after discharge from the rehabilitation center. Information was obtained from the patients using a mailed standardized questionnaire. Information regarding secondary cardiovascular events and treatment since discharge from the in-hospital rehabilitation clinic was obtained from the primary care physicians also by means of a standardized questionnaire. If a subject had died during follow-up, the death certificate was obtained from the local Public Health Department and the main cause of death was coded according to the International Classification of Diseases (9th Revision). Secondary cardiovascular events were defined either as cardiovascular disease (CVD) as the main cause of death (as stated in the death certificate), nonfatal myocardial infarction (MI), or ischemic cerebrovascular event (stroke). All nonfatal secondary events were reported by the primary care physicians.

Laboratory Methods
Blood at baseline was drawn at discharge from the rehabilitation center (on the average 43 days after the acute event; first quartile, 36 days; third quartile, 51 days) in a fasting state under standardized conditions. Plasma concentrations of Lp-PLA₂ were determined by a commercially available Lp-PLA₂ enzyme-linked immunosorbent assay (ELISA) kit (second generation PLAC^TM Test; diaDexus Inc, South San Francisco, Calif).²² The lower detection limit of Lp-PLA₂ in this assay is &2 ng/mL. The interassay coefficient of variation (CV) was between 6% and 7%. Lp-PLA₂ activity was measured in a 96-well microplate with a colorimetric substrate that is converted on hydrolysis by the phospholipase enzyme. Briefly, 25 µL of sample, or standard, or control are added per well, followed by addition of assay buffer plus substrate. The change in absorbance is immediately measured at 405 nm. The level of Lp-PLA2 activity in nmol/min per mL was calculated from the slope, based on a standard conversion factor from a p-Nitrophenol calibration curve. Mass and activity were moderately correlated (r=0.573, P<0.001).

CRP concentrations in plasma were measured by immunonephelometry on a Behring Nephelometer II (N Latex CRP mono; Dade-Behring, Marburg). Cystatin C was determined on the same device (Dade Behring, Marburg). NT-proBNP was measured by electrochemiluminescence on an Elecsys 170 (Roche Diagnostics, Mannheim, Germany). Interassay CV for CRP was 4.1%, for cystatin C it was 3.8%, and for NT-proBNP it was between 3% and 7%. All markers were measured in a blinded fashion. Blood lipids and leukocyte count were done by routine methods in both participating clinics.

Statistical Methods
First, the study population was described with respect to various sociodemographic and medical characteristics. The associations of sociodemographic characteristics, various cardiovascular risk factors, and medication with Lp-PLA₂ mass and activity (distribution in top tertile versus first and second) were quantified by means of a ² test. Partial Spearman correlation coefficients, adjusted for age and gender, were calculated for Lp-PLA₂ concentrations and activity and blood lipids, CRP, creatinine clearance, cystatin C, and NT-proBNP.

The relation of Lp-PLA₂ mass and activity with CVD events during follow-up was assessed by the Kaplan-Meier and life table method and quantified by means of the log-rank test. Then the Cox proportional hazards model was used to assess the independent association of Lp-PLA₂ mass and activity distribution with the risk of secondary CVD events. A basic model was adjusted for age (years) and gender. In addition (and to avoid over-adjustment), besides the main factor Lp-PLA₂ and the variables age, gender and hospital site, from a set of covariates (body mass index [BMI] kg/m²), smoking status (never, current, ex-smoker), duration of school education (<10 years, 10 years), family status (married, other), history of MI (yes, no), history of diabetes mellitus (yes, no), severity of CHD (number of affected vessels at baseline), HDL cholesterol (mg/dL), CRP (mg/L), cystatin C (mg/L), NT-proBNP (ng/mL), intake of ß-blockers, intake of ACE inhibitors, intake of diuretics, and hospital site (Isny, Bad Nauheim), only those were added to the model that were significant predictors of a secondary event at an level of 0.1 or that changed the parameter estimates for the main variables (Lp-PLA₂) by >10%. In further analyses LDL cholesterol was included also.

A receiver-operating curve was constructed after adjustment for covariates and the area under the curve (AUC) with its 95% confidence interval (CI) was calculated. In addition, Somer’s D, a measure of association between ordinal variables that provides a rank correlation between predicted and observed probabilities, was calculated for the various models. Somer’s D ranges between –1 and +1; 0 reflects no association at all. All statistical procedures were performed with the SAS statistical software package (release 8.2; SAS Institute Inc, Cary, NC) using the SAS-macro-package for prognostic modeling.²³

	Results

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Overall, 1206 patients with a diagnosis of CHD within the past 3 months were included in the study at baseline during the in-hospital rehabilitation program; 4.5-year follow-up information was complete for 1051 patients (87.2%). A total of 95 (9.0%) fatal and nonfatal CVD events occurred (30 cardiovascular deaths, 35 nonfatal MIs, and 30 strokes) during a mean follow-up time of 48.7 months (SD 15.9).

Table 1 shows the main characteristics of the study population. Of the 1051 patients with a diagnosis of CHD, 58.2% had reported a history of MI, and 42.7% of patients (with coronary angiography) had 3-vessel disease. The mean age of CHD patients was 59 years; most of them (56.5%) were between 60 to 70 years old, and 84.9% were male. The initial invasive management of CHD in the acute care hospital was percutaneous coronary intervention (PCI) in 361 (21.9%) and coronary artery bypass grafting (CABG) in 499 (28.1%) patients.

View this table: [in this window] [in a new window]   TABLE 1. Sociodemographic, Clinical, and Laboratory Characteristics in 1051 Patients With Clinically Manifest Coronary Heart Disease

Table 2 shows the relationship of various cardiovascular risk factors, clinical severity of CHD, and medication with Lp-PLA₂ mass and activity. For Lp-PLA₂ mass, females were more likely to be in the top tertile of the Lp-PLA₂ distribution than men. Also, higher age, history of MI, more advanced coronary artery disease (as determined by angiography), not taking an ACE inhibitor and, as expected, particularly the lack of statin treatment, were all strongly and positively related to Lp-PLA₂ distribution; there was no association with BMI, smoking status, history of diabetes, and ß-blocker or diuretic intake. For Lp-PLA₂ activity, similar relationships were seen with gender, clinical score, and statin treatment, but not with age, history of MI, and ACE inhibitor intake. High Lp-PLA₂ activity was seen more frequently in those on a diuretic compared with those without.

View this table: [in this window] [in a new window]   TABLE 2. Levels of Various Factors and Proportion in the TopTertile of the Lp-PLA2Distribution (Mass and Activity)

Table 3 shows correlations between lipid variables, other emerging risk factors and Lp-PLA₂ mass and activity (adjusted for age and gender). Total cholesterol (r=0.345 and r=0.490) and LDL cholesterol (r=0.423 and r=0.564) were strongly and positively correlated with Lp-PLA₂ mass and activity; HDL cholesterol showed a moderately negative correlation, and comparable small positive correlations for both parameters were seen with CRP, cystatin C, and with NT-proBNP. All correlation coefficients were statistically significant (P<0.0001).

View this table: [in this window] [in a new window]   TABLE 3. Partial Spearman Rank Correlation Coefficients (R) Between Lipid Variables, C-Reactive Protein, Creatinine Clearance, Cystatin C, NT-proBNP, and Lp-PLA2 Concentrations and Activity After Adjustment for Age and Gender

Figurea and b shows Kaplan-Meier curves presenting the proportion of patients with secondary CVD events according to tertiles of Lp-PLA₂ mass (and activity) at baseline_. Of patients in the bottom tertile of Lp-PLA₂, 5.8% (5.2%) experienced an event compared with 10.7% (10.0%) and 10.6% (11.9%) in the middle and upper tertile, respectively (P<0.03 and P<0.01, respectively).

View larger version (17K): [in this window] [in a new window]   A, Kaplan-Meier estimates of secondary fatal and non-fatal CVD events during follow-up (time=days) according to tertiles of Lp-PLA2 mass at baseline. B, Kaplan-Meier estimates of secondary fatal and nonfatal CVD events during follow-up (time=days) according to tertiles of Lp-PLA2 activity at baseline

Table 4 shows the results of multivariable analysis to estimate the independent association of Lp-PLA₂ concentrations and activity at baseline with risk of fatal and nonfatal cardiovascular events during follow-up. In age- and gender-adjusted analysis, patients in the top tertile compared with those in the bottom tertile of the Lp-PLA₂ mass distribution at baseline had a hazard ratio (HR) of 1.79 (95% confidence interval [CI], 1.04 to 3.08) for a CVD event (P for trend <0.05). The HR increased after adjustment for classical risk factors, severity of CHD, and all factors from Table 2 contributing significantly (P<0.1) to the model or which changed the main effect of Lp-PLA₂ by >10% (which were BMI, HDL cholesterol, history of MI, history of diabetes mellitus, treatment with ACE inhibitors, cystatin C, and NT-proBNP), resulting in a HR for the top tertile of 2.65 (95% CI, 1.47 to 4.76). If CRP, which did not qualify for an inclusion into the model, was included, the HR even increased slightly further (HR in the top tertile 2.70) (95% CI, 1.49 to 4.90). Final adjustment for LDL cholesterol led to an expected decrease of the association (HR for top tertile 2.09; 95% CI, 1.10 to 3.96), which, however, was still statistically significant. For Lp-PLA₂ activity, in the multivariate model, the HR was slightly lower (HR in the top tertile 2.40; 95% CI, 1.35 to 4.29) and also decreased after adjustment for LDL cholesterol (HR in the top tertile 1.81; 95% CI, 0.94 to 3.49), but in contrast to Lp-PLA₂ mass the 95% CI included the null value.

View this table: [in this window] [in a new window]   TABLE 4. Association of Lp-PLA2 Concentrations and Activity at Baseline With Fatal and Nonfatal Cardiovascular Events During Follow-Up

In Table 5 we quantified the incremental contribution of Lp-PLA₂ mass to risk prediction in the presence of classical risk factors, renal function, and hemodynamic stress. As can be seen from receiver operating characteristics (ROC) curve analyses, the addition of cystatin C and NT-proBNP to a basic model improved the predictive accuracy of the model (AUC from 0.67 to 0.71). After additional inclusion of Lp-PLA₂ mass, there was still a further, however smaller, increase (AUC from 0.71 to 0.73).

View this table: [in this window] [in a new window]   TABLE 5. Predicitive Accuracy of Various Multivariate Models (see Table 4 second last column) as Measured by an Increase in the Area Under the Receiver-Operating Characteristic (ROC) Curve and Somer D After Inclusion of Several Biomarkers.

	Discussion

Top Abstract Introduction Materials and Methods Results Discussion References

 
These data from a large cohort of patients with manifest CHD strongly suggest a role for Lp-PLA₂ as a novel predictor of cardiovascular risk in a population at high risk for future CVD events. In multivariable analyses after adjusting for a wide range of established risk factors including markers of inflammation, renal function, and hemodynamic stress, there was still an &2-fold increased risk for future CVD events in patients in the upper 2 tertiles of Lp-PLA₂ mass compared with the bottom tertile; for Lp-PLA₂ activity, risk estimates were only slightly smaller and failed to reach statistical significance after full adjustment for covariates. Therefore, especially Lp-PLA₂ mass may be a promising biomarker for risk prediction in secondary prevention of CVD.

Associations of Lp-PLA₂ With Other Risk Markers
Lp-PLA₂ mass and activity were strongly positively correlated with LDL and total cholesterol and moderately negatively with HDL cholesterol, as described in previous studies^17–21 reflecting mainly the close association with LDL cholesterol. Markers of inflammation, renal function, and hemodynamic stress were also positively correlated in our study. Small associations with age have also been seen in these studies.^17–21 A relationship with gender was no longer present in the study by Brilakis²¹ after adjustment for HDL cholesterol. Initial concentrations in men were higher than in women, which was the opposite way in our study. In univariate analysis, we found an association with the severity of CHD (P<0.001), which was also reported by Brilakis et al.²¹ However, in the latter study, the association was no longer present after adjusting for clinical and lipid variables.

Furthermore, an expected association was seen with statin intake; statins lower Lp-PLA₂ mass and activity,^24,25 thus it is conceivable that those not on a statin had higher concentrations and activity. However, the inverse association for Lp-PLA₂ mass with ACE inhibitor intake as seen in univariate analysis may represent confounding by indication as patients at high risk may more likely receive these drugs. Yet there are no observations that ACE inhibitors may lower plasma concentrations of Lp-PLA_2.

Lp-PLA₂ and Prediction of Cardiovascular Events in Patients With Manifest CHD
In the only other study in patients with mainly stable CHD in which the prognostic value of Lp-PLA₂ has been studied,²¹ 466 consecutive patients scheduled for coronary angiography were followed for a median of 4 years. During this time period, 72 events occurred in 61 patients. Baseline concentrations of Lp-PLA₂ mass were higher in CHD patients who later on developed an adverse event compared with those who did not. The relative risk for a future event for a one standard deviation increase in Lp-PLA₂ mass was 1.30 after multivariable adjustments and thus comparable to data from primary risk studies such as WOSCOPS¹⁷ and MONICA.¹⁹

Our study participants were about the same age as those in the study by Brilakis et al,²¹ Lp-PLA₂ concentrations were in the same range, and the follow-up period was similar. When looking at Kaplan-Meier estimates, striking similarities between the 2 studies can be seen. Using comparable cut-points, the second and third tertiles were clearly different from the bottom tertile in both studies, suggesting a cut-point for increased risk rather than a linear association. Similar results were seen for Lp-PLA₂ activity, which is also in accordance with the Rotterdam study in initially healthy subjects.²⁰

However, our study has several advantages and extends the results of the previous study. First, the patient population was more than twice as large as the one by Brilakis et al and had more atherosclerosis specific end points as we did not include the need for revascularization or all-cause mortality. Second, the study population was more homogeneous because only patients weeks after an acute event were included. Finally, we were able to measure simultaneously Lp-PLA₂ mass and activity and considered also markers of inflammation like CRP, cystatin C, a strong indicator of renal function, and NT-proBNP, an established marker of hemodynamic stress. The latter 2 markers have been reported to be independently linked to future cardiovascular outcome in patients with CHD.^26–30 Even after taking into account these emerging predictors, Lp-PLA₂ mass in our cohort added incremental prognostic information. Thus, it seems hat the risk prediction associated with elevated concentrations of Lp-PLA₂ is rather stable and yields clinically relevant information to the already known established and laboratory risk factors in a population at already high cardiovascular risk.

Interestingly, our data are supported by those published by O’Donoghue et al³¹ from the PROVE IT-TIMI 22 trial suggesting that Lp-PLA₂ activity or mass may not be predictive for recurrent events when measured at the time of admission to hospital or early after an acute coronary syndrome, but indeed may be able to modify risk prediction when measured some time apart from the acute events eg, at day 30. In that study, in 3648 patients with acute coronary syndrome, Lp-PLA₂ activity and mass were measured at baseline and 30 days later (n=3625). Patients with an elevated Lp-PLA₂ activity but not mass in the top quintile at day 30 had a 33% increased risk for recurrent events (RR, 1.33; 95% CI, 1.01 to 1.74) over 24 months of follow-up.

In contrast to prospective cohorts with clinical end points, data from a large cross-sectional study using intima media thickness of the carotid arteries as a measure of subclinical atherosclerosis³² showed no independent association with Lp-PLA₂ activity after adjustment for cholesterol. Because Lp-PLA₂ travels with LDL cholesterol in the peripheral circulation, a consistent correlation between these 2 variables has been reported in all studies. Thus, adjusting for (LDL) cholesterol clearly is associated with an attenuation of the association between Lp-PLA₂ and the end point under study. In the majority of studies on (inflammatory) biomarkers, a moderate or even strong association has been reported between elevated concentrations in blood and clinical end points but the association with subclinical atherosclerosis or atherosclerotic burden/extent has been negative in almost all studies.

Measurement of Lp-PLA₂ Mass Versus Activity
Results from WOSCOPS¹⁷ and MONICA,¹⁹ which measured mass, and from the Rotterdam study,²⁰ which measured activity, suggest reasonable agreement between both methods. However, there is a lack of data comparing the predictive value of Lp-PLA₂ mass and activity in the same population.

Most recently, in the PROVE-IT TIMI 22 trial³¹ only a modest correlation of r=0.36 between activity and mass was found. Irribarren et al³³ measured both parameters in the CARDIA study and found a correlation between mass and activity of r=0.61, which is comparable to our study (r=0.57). These authors also reported a stronger correlation between activity compared with mass with LDL cholesterol (r=0.52 and r=0.39, respectively), which is similar to correlations we found (activity r=0.56 and mass r=0.42, respectively). Thus, as suggested by these authors, the loss of statistical significance for activity versus mass in multivariable prediction models, may be, at least in part, attributable to its stronger correlation with LDL cholesterol. Certainly, more studies are needed to resolve these issues.

Study Limitations
The following limitations of our study should be considered. Although we had a large sample of patients with CHD (>50% with a history of MI), fatal CVD events were limited in this study population. This is explained by the fact that mortality of MI is highest during the prehospital and early in-hospital phase. Because the acute events leading to diagnosis of CHD or MI had occurred at least 3 weeks before inclusion in this study, selection of patients with a better prognosis compared with a patient population within the early phase of a newly diagnosed CHD must be assumed. Furthermore, not all patients were willing or able to participate in an in-hospital rehabilitation program. This may be a further reason for the under-representation of severely ill patients in our study sample. However, this does not explain the positive findings between Lp-PLA₂ and CVD events, but suggests that the true prognostic value of Lp-PLA₂ may even be stronger than shown in our study.

Conclusion
These data are in support of an important prognostic value of Lp-PLA₂ among patients with known CHD. These data strongly suggest that especially Lp-PLA₂ mass is a useful clinical biomarker, which is independent of traditional risk factors and other emerging risk factors like CRP, cystatin C, and NT-proBNP, and may be superior to measurements of activity. If causal involvement in the pathogenesis of atherosclerosis can be proven, Lp-PLA₂ may become a promising target for intervention in the future.

	Acknowledgments

 
We highly appreciate the technical assistance of Gerlinde Trischler.

Sources of Funding

This research was supported by an unrestricted grant from diaDexus, Inc, South San Francisco, California.

Disclosures

W.K. has received honoraria for lectures from diaDexus and GSU. The other authors have no disclosures.

	Footnotes

 
Original received February 22, 2005; final version accepted April 6, 2006.

	References

Top Abstract Introduction Materials and Methods Results Discussion References

 

1. Macphee C, Benson GM, Shi Y, Zalewski A. Lipoprotein-associated phospholipase A2: a novel marker of cardiovascular risk and potential therapeutic target. Expert Opin Investig Drugs. 2005; 14: 671–679.[Medline] [Order article via Infotrieve]
2. Tselepis AD, Chapman JM. Inflammation, bioactive lipids and atherosclerosis: potential roles of a lipoprotein-associated phospholipase A2, platelet activating factor-acetylhydrolase. Atherosclerosis. 2002; Suppl 3: 57–68.
3. Stafforini DM, Elstad MR, McIntyre TM, Zimmerman GA, Prescott SM. Human macrophages secret platelet-activating factor acetylhydrolase. J Biol Chem. 1990; 265: 9682–9687.[Abstract/Free Full Text]
4. Asano K, Okamoto S, Fukunaga K, Shiomi T, Mori T, Iwata M, Ikeda Y, Yamaguchi K. Cellular source(s) of platelet-activating-factor acetylhydrolase activity in plasma. Biochem Biophys Res Commun. 1999; 261: 511–514.[CrossRef][Medline] [Order article via Infotrieve]
5. Tarbet EB, Stafforini DM, Elstad MR, Zimmerman GA, McIntyre TM, Prescott SM. Liver cells secrete the plasma form of platelet-activating factor acetylhydrolase. J Biol Chem. 1991; 266: 16667–16673.[Abstract/Free Full Text]
6. Hakkinen T, Luoma JS, Hiltunen MO, Macphee CH, Milliner KJ, Patel L, Rice SQ, Tew DG, Karkola K, Yla-Herttuala S. Lipoprotein-associated phospholipase A₂, platelet-activating factor acetylhydrolase, is expressed by macrophages in human and rabbit atherosclerotic lesions. Arterioscler Thromb Vasc Biol. 1999; 19: 2909–2917.[Abstract/Free Full Text]
7. Kolodgie F, Burke A, Taye A, Liu W, Sudhir K, Virmani R. Lipoprotein-associated phospholipase A2 is highly expressed in macrophages of coronary lesions prone to rupture. Circulation. 2004; 110 (suppl III): III-246. Abstract.
8. Caslake MJ, Packard CJ, Suckling KE, Holmes SD, Chamberlain P, Macphee CH. Lipoprotein-associated phospholipase A₂, platelet-activating factor acetylhydrolase: a potential new risk factor for coronary artery disease. Atherosclerosis. 2000; 150: 413–419.[CrossRef][Medline] [Order article via Infotrieve]
9. Tsimihodimos V, Karabina SA, Tambaki AP, Bairaktari E, Miltiadous G, Goudevenos JA, Cariolou MA, Chapman MJ, Tselepis AD, Elisaf M. Altered distribution of platelet-activating factor-acetylhydrolase activity between LDL and HDL as a function of the severity of hypercholesterolemia. J Lipid Res. 2002; 43: 256–263.[Abstract/Free Full Text]
10. Macphee CH, Moores KE, Boyd HF, Dhanak D, Ife RJ, Leach CA, Leake DS, Milliner KJ, Patterson RA, Suckling KE, Tew DG, Hickey DM. Lipoprotein-associated phospholipase A₂, platelet-activating factor acetylhydrolase, generates two bioactive products during the oxidation of low-density lipoprotein: use of a novel inhibitor. Biochem J. 1999; 338: 479–487.
11. Kume N, Cybulsky MI, Gimbrone MA. Jr. Lysophosphatidylcholine, a component of atherogenic lipoproteins, induces mononuclear leukocyte adhesion molecules in cultured human and rabbit arterial endothelial cells. J Clin Invest. 1992; 90: 1138–1144.[Medline] [Order article via Infotrieve]
12. Quinn MT, Parthasarathy S, Steinberg D. Lysophosphatidylcholine: a chemotactic factor for human monocytes and its potential role in atherogenesis. Proc Natl Acad Sci U S A. 1988; 85; 2805–2809.[Abstract/Free Full Text]
13. Leach CA, Hickey DM, Ife RJ, Macphee CH, Smith SA, Tew DG. Lipoprotein-associated PLA₂ inhibition-a novel, non-lipid lowering strategy for atherosclerosis therapy. Farmaco. 2001; 56: 45–50.[CrossRef][Medline] [Order article via Infotrieve]
14. Blackie JA, Bloomer JC, Brown MJ, Cheng HY, Elliott RL, Hammond B, Hickey DM, Ife RJ, Leach CA, Lewis VA, Macphee CH, Milliner KJ, Moores KE, Pinto IL, Smith SA, Stansfield IG, Stanway SJ, Taylor MA, Theobald CJ, Whittaker CM. The discovery of SB-435495. A potent, orally active inhibitor of lipoprotein-associated phospholipase A(2) for evaluation in man. Bioorg Med Chem Lett. 2002; 12: 2603–2606.[CrossRef][Medline] [Order article via Infotrieve]
15. Blackie JA, Bloomer JC, Brown MJ, Cheng HY, Hammond B, Hickey DM, Ife RJ, Leach CA, Lewis VA, Macphee CH, Milliner KJ, Moores KE, Pinto IL, Smith SA, Stansfield IG, Stanway SJ, Taylor MA, Theobald CJ. The identification of clinical candidate SB-480848: a potent inhibitor of lipoprotein-associated phospholipase A₂. Bioorg Med Chem Lett. 2003; 13: 1067–1070.[CrossRef][Medline] [Order article via Infotrieve]
16. Johnson A, Zalewski A, Janmohamed S, Sawyer J, Rolfe T, Staszkiewicz W, Alvarez S. Lipoprotein-associated phospholipase A₂ activity, an emerging CV risk marker, can be inhibited in atherosclerotic lesions and plasma by novel pharmacologic intervention: the results of a multicenter clinical study. Circulation. 2004; 110 (suppl III): III-590 Abstract.
17. Packard CJ, O’Reilly DS, Caslake MJ, McMahon AD, Ford I, Cooney J, Macphee CH, Suckling KE, Krishna M, Wilkinson FE, Rumley A, Lowe GD. Lipoprotein-associated phospholipase A₂ as an independent predictor of coronary heart disease. West of Scotland Coronary Prevention Study Group. N Engl J Med. 2000; 343: 1148–1155.[Abstract/Free Full Text]
18. Ballantyne CM, Hoogeveen RC, Bang H, Coresh J, Folsom AR, Heiss G, Sharrett AR. Lipoprotein-associated phospholipase A₂, high-sensitivity C-reactive protein, and risk for incident coronary heart disease in middle-aged men and women in the Atherosclerosis Risk in Communities (ARIC) study. Circulation. 2004; 109: 837–842.[Abstract/Free Full Text]
19. Koenig W, Khuseyinova N, Lowel H, Trischler G, Meisinger C. Lipoprotein-associated phospholipase A₂ adds to risk prediction of incident coronary events by C-reactive protein in apparently healthy middle-aged men from the general population: results from the 14-year follow-up of a large cohort from southern Germany. Circulation. 2004; 110: 1903–1908.[Abstract/Free Full Text]
20. Oei HH, van der Meer IM, Hofman A, Koudstaal PJ, Stijnen T, Breteler MM, Witteman JC. Lipoprotein-associated phospholipase A₂ activity is associated with risk of coronary heart disease and ischemic stroke: the Rotterdam Study. Circulation. 2005; 111: 570–575.[Abstract/Free Full Text]
21. Brilakis ES, McConnell JP, Lennon RJ, Elesber AA, Meyer JG, Berger PB. Association of lipoprotein-associated phospholipase A₂ levels with coronary artery disease risk factors, angiographic coronary artery disease, and major adverse events at follow-up. Eur Heart J. 2005; 26: 137–144.[Abstract/Free Full Text]
22. Hoogeveen RC, Ballantyne CM. PLAC test for identification of individuals at increased risk for coronary heart disease. Expert Rev Mol Diagn. 2005; 5: 9–14.[CrossRef][Medline] [Order article via Infotrieve]
23. Muche R, Ring C, Ziegler C. A SAS macro package for development and validation of prognostic and diagnostic models based on the logistic regressions model. Biom J. 2004; 46 (S1): 154. Abstract.[CrossRef]
24. Albert MA, Glynn RJ, Wolfert RL, Ridker PM. The effect of statin therapy on lipoprotein associated phospholipase A2 levels. Atherosclerosis. 2005; 182: 193–198.[Medline] [Order article via Infotrieve]
25. Caslake MJ, Packard CJ. Lipoprotein-associated phospholipase A₂ as a biomarker for coronary disease and stroke. Nat Clin Pract Cardiovasc Med. 2005; 2: 529–535.[CrossRef][Medline] [Order article via Infotrieve]
26. Koenig W, Twardella D, Brenner H, Rothenbacher D. Plasma concentrations of cystatin C in patients with coronary heart disease and risk for secondary cardiovascular events: more than simply a marker of glomerular filtration rate. Clin Chem. 2005; 51: 321–327.[Abstract/Free Full Text]
27. Jernberg T, Lindahl B, James S, Larsson A, Hansson LO, Wallentin L. Cystatin C: a novel predictor of outcome in suspected or confirmed non-ST-elevation acute coronary syndrome. Circulation. 2004; 110: 2342–2348.[Abstract/Free Full Text]
28. Rothenbacher D, Koenig W, Brenner H. Prognostic value of N-terminal pro-B natriuretic peptide levels: prospective cohort study in patients with stable coronary heart disease. Eur Heart J. 2005; 26 (Abstract Supplement): P1694. Abstract.
29. Jernberg T, Stridsberg M, Venge P, Lindahl B. N-terminal pro brain natriuretic peptide on admission for early risk stratification of patients with chest pain and no ST-segment elevation. J Am Coll Cardiol. 2002; 40: 437–445.[Abstract/Free Full Text]
30. de Lemos JA, Morrow DA, Bentley JH, Omland T, Sabatine MS, McCabe CH, Hall C, Cannon CP, Braunwald E. The prognostic value of B-type natriuretic peptide in patients with acute coronary syndromes. N Engl J Med. 2001; 345: 1014–1021.[Abstract/Free Full Text]
31. O’Donoghue M, Morrow DA, Sabatine MS, Murphy SA, McCabe CH, Cannon CP, Braunwald E. Lipoprotein-associated phospholipase A₂ and its association with cardiovascular outcomes in patients with acute coronary sSyndromes in the PROVE IT-TIMI 22 (PRavastatin Or atorVastatin Evaluation and Infection Therapy-Thrombolysis In Myocardial Infarction) Trial. Circulation. 2006;[Epub ahead of print, March 14].
32. Kardys I, Oei HH, van der Meer IM, Hofman A, Breteler MM, Witteman JC. Lipoprotein-associated phospholipase A₂ and measures of extracoronary atherosclerosis: The Rotterdam Study. Arterioscler Thromb Vasc Biol. 2006; 26: 631–636.[Abstract/Free Full Text]
33. Iribarren C, Gross MD, Darbinian JA, Jacobs DR, Sidney S, Loria CM. Association of lipoprotein-associated phospholipase A₂ mass and activity with calcified coronary plaque in young adults. The CARDIA study. Arterioscler Thromb Vasc Biol. 2005; 25: 216–221.[Abstract/Free Full Text]

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