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Prognostic Value of Plasma Myeloperoxidase in ESRD Patients
Angela Yee-Moon Wang, MD, PhD, FRCP,1* Christopher Wai-Kei Lam, PhD, FACB,2,3
Iris Hiu-Shuen Chan, PhD,2 Mei Wang, PhD,1* Siu-Fai Lui, FRCP,1 andJohn E. Sanderson, MD, FRCP1
Background: Myeloperoxidase (MPO) has been suggested to have a role in atherosclerosis throughits strong oxidative capacity. We hypothesized that MPO level may predict clinical outcomes in patientswith end-stage renal disease receiving long-term peritoneal dialysis (PD) therapy.
Study Design: Prospective cohort study.Setting & Participants: 236 long-term PD patients were recruited from a single regional dialysis unit
in Hong Kong between April 1999 and February 2001.Predictor: Level of plasma MPO, analyzed using a sandwich enzyme-linked immunosorbent assay.Outcome & Measurement: Mortality and fatal or nonfatal cardiovascular events at 3 years.Results: The distribution of MPO levels was skewed with a median of 31.8 �g/L (25th-75th
percentiles, 24.4-42.7). There were 69 deaths and 81 cardiovascular events. Adjusting for traditionaland nontraditional risk factors and C-reactive protein, cardiac troponin T, and N-terminal pro-brainnatriuretic peptide levels, a doubling in plasma MPO level was associated independently with a 46%(95% CI, 1.02-2.08; P � 0.04) and 60% (95% CI, 1.17-2.18; P � 0.003) increase in risks of mortality andcardiovascular events, respectively. Log2MPO showed significant additional predictive value for mortal-ity (P � 0.04) and cardiovascular events (P � 0.005) when included in Cox regression modelsconsisting of clinical, demographic, dialysis, echocardiographic, and biochemical parameters, as well asC-reactive protein, cardiac troponin T, and N-terminal pro-brain natriuretic peptide levels.
Limitations: MPO was measured at a single time and did not reflect changes over time.Conclusions: These data suggest that plasma MPO level has significant independent and additional
prognostic value beyond the standard clinical, biochemical, and echocardiographic parameters and isuseful for outcome stratification in long-term PD patients. MPO may be an important mediator ofincreased cardiovascular risk in patients with end-stage renal disease and warrants further investigation.Am J Kidney Dis 56:937-946. © 2010 by the National Kidney Foundation, Inc.
INDEX WORDS: Myeloperoxidase; end-stage renal disease; mortality; cardiovascular events; perito-neal dialysis.
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yeloperoxidase (MPO) is a hemoproteinfound in the azurophilic granules of neu-
rophils and, to a lower extent, in monocytes andacrophages and is involved mainly in innate
mmune defense and bactericidal activity.1 Inddition, MPO functions as a major enzymaticatalyst for the initiation of lipid peroxidation, aivotal process in atherogenesis, at sites of inflam-ation.2-4 MPO serves as a catalytic sink for
itric oxide, decreases nitric oxide bioavailabil-ty, and impairs nitric oxide–dependent vasodila-ation.5,6 Plasma MPO level predicts nitric oxide–ependent flow-mediated dilatation in humans.7
n immunohistochemical studies, MPO and prod-cts of MPO-catalyzed oxidation reactions haveeen identified in human atherosclerotic le-ions.1,8-11
Increased plasma MPO level predicts the sever-ty of angiographic coronary artery disease12 anddverse cardiac outcomes in patients with acuteoronary syndromes independent of C-reactiverotein (CRP) level.13 Furthermore, patients with
polymorphism of the MPO gene, a G to American Journal of Kidney Diseases, Vol 56, No 5 (November), 2
ransition at position �463 of the promoter re-ion, showed a 2-fold decrease in MPO expres-ion and had markedly decreased angiographicvidence of coronary artery disease, nonfatalyocardial infarction, and cardiac death.14,15
ore recently, a study of hemodialysis patients
From the Departments of 1Medicine and Therapeuticsnd 2Chemical Pathology, The Chinese University of Hongong, Prince of Wales Hospital, Shatin, New Territories,ong Kong; and 3Macau Institute for Applied Research inedicine and Health, Macau University of Science and
echnology, Taipa, Macau.* Current affiliation: Department of Medicine, Queenary Hospital, University of Hong Kong, Hong Kong.Received January 14, 2010. Accepted in revised form May
, 2010. Originally published online as doi:10.1053/j.ajkd.010.05.008 on July 20, 2010.Address correspondence to Angela Yee-Moon Wang, MD,
hD, FRCP, University Department of Medicine, The Univer-ity of Hong Kong, Queen Mary Hospital, 102 Pokfulam Rd,okfulam, Hong Kong. E-mail: [email protected]© 2010 by the National Kidney Foundation, Inc.0272-6386/10/5605-0018$36.00/0
doi:10.1053/j.ajkd.2010.05.008010: pp 937-946 937
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eported an association between plasma MPOevel and mortality.16 Patients with end-stageenal disease (ESRD) with the G to A transitionn the MPO promoter had a lower prevalence oflinical cardiovascular disease.17 Thus, labora-ory, clinical, and genetic studies have lent strongupporting evidence that MPO may have anmportant role in atherogenesis.
Given this background, the primary objectivef this study is to evaluate whether plasma MPOevel has prognostic value for mortality andardiovascular events beyond the standard clini-al, biochemical, and echocardiographic parame-ers in patients on long-term peritoneal dialysisPD) therapy.
METHODS
tudyDesign
This is a prospective cohort study conducted in a singleegional dialysis center in Hong Kong. Study participantsere recruited between April 1999 and February 2001 androspectively followed up for 3 years. The study protocolas approved by the Clinical Research Ethics Committee of
he Chinese University of Hong Kong. All patients providednformed consent before study entry.
esearchParticipants
Patients were considered eligible for study entry if theyad ESRD and had been maintained on continuous PDreatment for 3 months or longer. Exclusion criteria includedatients with underlying active malignancy, chronic liverisease, systemic lupus erythematosus with ongoing activeupus activity requiring immunosuppression, systemic vascu-itis, chronic rheumatic heart disease, and congenital heartisease; patients who refused to give consent; or patientsith incomplete data. Based on inclusion and exclusion
riteria, 236 long-term PD patients were recruited, represent-ng 82.1% of the total PD population in the center. Allatients were dialyzed using conventional lactate-bufferedlucose-based PD solutions.In patients who developed acute coronary syndrome,
cute heart failure, peritonitis, exit-site infections, or othernfective complications, all of the following baseline assess-ents were deferred for at least 1 month after complete
esolution of the complication.
iochemical Analysis
A 20-mL fasting venous blood sample was collected attudy baseline for measurement of blood hemoglobin andlasma MPO, cardiac troponin T (cTnT), N-terminal pro-rain natriuretic peptide (NT-pro-BNP), high-sensitivity CRP,lbumin, urea, creatinine, calcium, phosphorus, and lipidrofile. MPO was measured using a sandwich enzyme-inked immunosorbent assay kit (Immunodiagnostik AG,ww.immundiagnostik.com) with a lower detection limit of
.6 �g/L. Our study-specific intra- and interassay coeffi- fients of variation were 8.5% and 10.2% at 4.8 �g/L and.8% and 7.2% at 32.3 �g/L, respectively. cTnT and NT-pro-NP were quantified using electrochemiluminescence immu-oassay (Elecsys 2010 analyzer; Roche Diagnostic GmbH,ww.roche.de). High-sensitivity CRP was measured using
hemiluminescence immunoassay with the IMMULITE Ana-yzer (Siemens Medical Solutions Diagnostics, www.medical.iemens.com). Albumin was measured using the bromcresolurple method, and total cholesterol and triglyceride, usingnzymatic assay on the Hitachi 911 analyzer (Roche Diag-ostics GmbH). High-density lipoprotein cholesterol waseasured after precipitation of apolipoprotein B–containing
ipoproteins with phosphotungstate, whereas low-densityipoprotein cholesterol was calculated using the Friedewaldormula.18 Twenty-four–hour dialysate and simultaneousrine samples were collected for measurement of residualidney function and dialysis adequacy. Residual glomerularltration rate was measured as the average of 24-hour urinerea and creatinine clearance.19 Adequacy of dialysis wasstimated by measuring total weekly urea clearance (Kt/V)nd creatinine clearance using standard methods.20 Contribu-ion of the PD and kidney components to total urea clearanceas estimated separately.
linical DataCollection
Demographic and clinical data were collected prospec-ively at baseline using direct patient inquiry and review ofhe computerized medical record system. Clinical atheroscle-otic vascular disease was defined as the presence of coro-ary artery disease (indicated by previous myocardial infarc-ion or stable or unstable angina with or without a history oforonary artery bypass surgery or percutaneous coronaryntervention), cerebrovascular disease (indicated by a his-ory of stroke, carotid endarterectomy, or stent placement),nd peripheral vascular disease (indicated by the presence ofntermittent claudication or leg pain at rest, together withlinical signs of peripheral vascular disease with or withouthistory of amputation or revascularization). Body mass
ndex was calculated as body weight in kilograms divided byeight in meters squared.
chocardiographicDataCollection
Two-dimensional echocardiography was performed usingGE-VingMed System 5 echocardiographic machine (GE-ingMed Sound AB, www.vingmed.se) with a 3.3-mHzultiphase-array probe in patients lying in the left decubitus
osition by a single experienced cardiologist blinded to alllinical details of patients except body weight, height, age,nd sex. The cardiologist performing echocardiography wasot involved in the clinical management of patients. Echocar-iographic data were recorded according to the guidelines ofhe American Society of Echocardiography.21 Left ventricu-ar (LV) mass was calculated using the modified Americanociety of Echocardiography cube formula proposed byevereux et al22 and indexed by body surface area.
ollow-up
All patients were followed up prospectively for 3 yearsrom the day of baseline assessments or until death. The
ollow-up period ended in February 2004. No patient was
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Myeloperoxidase in Kidney Failure 939
ost to follow-up. The outcomes evaluated were death fromll causes and fatal or nonfatal cardiovascular event. Foratients who developed multiple cardiovascular events, sur-ival analysis was limited to the first event. Cardiovascularvent included acute myocardial ischemic event, stroke,ustained atrial or ventricular arrhythmia, peripheral vascu-ar disease, and sudden cardiac death defined and diagnosedlinically as unexpected natural death within 1 hour fromymptom onset and without a prior condition that wouldppear fatal.23,24 Acute myocardial ischemia was diagnosedy the attending physician based on the presence of symp-oms and serial electrocardiographic and cardiac enzymehanges in accordance with World Health Organizationriteria. Cause of death and nature of the first cardiovascularvent were established by the attending physicians, who hado knowledge of baseline plasma MPO results. In case ofeath out of the hospital, family members were interviewedy telephone to ascertain the circumstances surroundingeath.
tatistical Analysis
Continuous data are expressed as mean � standard devia-ion or median (25th, 75th percentiles) depending on theistribution, and categorical data, as percentage. Patientsere stratified by tertiles of plasma MPO. Between-group
omparisons were performed using 1-way analysis of vari-nce, Kruskal-Wallis test, or �2 test, when appropriate.ivariate correlation analysis was performed to evaluateorrelations of different factors with plasma MPO levels. Iniew of the skewed distribution, plasma MPO level wasog2-transformed before performing correlation analysis.
Cumulative survival curves were generated using theaplan-Meier method, and between-group survival was com-ared using log-rank test. In this analysis, patients whonderwent kidney transplant or transferred to hemodialysisherapy during the 3-year follow-up were censored at theime of transfer to alternative kidney replacement therapy. If
patient died within 3 months of transfer to hemodialysisherapy, he or she was not censored because the earlyortality was considered to reflect health status during the
eriod of failing PD treatment. We used a Cox proportionalazards model to estimate hazard ratios (HRs) of all-causeortality and cardiovascular event in relation to log2MPO
nd with stepwise adjustment for traditional risk factorsage, male sex, smoking history, diabetes, background athero-clerotic vascular disease, hypertension, and low-densityipoprotein cholesterol level), kidney disease–related riskactors (serum albumin level, hemoglobin level, calcium-hosphorus product, duration of dialysis therapy, residuallomerular filtration rate, and LV mass index), CRP level,T-pro-BNP level, and cTnT level. We plotted scaled Schoen-
eld residuals versus time for all variables and computedheir correlations against time to confirm that all variablesonsidered in the Cox regression analysis met the assump-ions of proportional hazards.
We performed receiver operating characteristic (ROC)urve analysis to investigate the predictive value for all-ause mortality and first cardiovascular event at 3 years bydding CRP, cTnT, NT-pro-BNP, and log2MPO values to theodel including standard clinical, demographic, biochemi-
al, dialysis, and echocardiographic parameters. A risk score a
or each participant based on each model was calculated byhe sum of the products of the coefficient estimates from theox models for all-cause mortality and first cardiovascularvent and the values of the variable for each patient. Thisisk score then was used in the ROC curve analysis toalculate the area under the curve, which is the Harrelllobal C statistic for censored responses.25
The incremental prognostic value of log2MPO over thetandard clinical, demographic, biochemical, dialysis, andchocardiographic parameters was assessed using a modi-ed stepwise procedure in 4 modeling steps. In brief, modeladjusted for traditional risk factors. Model 2 adjusted for
actors in model 1 and serum albumin level, hemoglobinevel, calcium-phosphorus product, duration of dialysisherapy, residual glomerular filtration rate, and LV massndex. Model 3 adjusted for factors in model 2 and CRPevel. Model 4 adjusted for factors in model 3 and cTnT andT-pro-BNP levels. A significant improvement in modelrediction was based on the �2 log likelihood ratio statistic,hich followed a �2 distribution, and P value was based on
he incremental value compared with the previous model.All statistical analysis was performed using SPSS, version
6.0 (SPSS Inc, www.spss.com). All P values were 2 tailed.� 0.05 was considered to be statistically significant.
RESULTS
Baseline patient characteristics are listed inable 1. Causes of ESRD were chronic glomeru-
onephritis in 75 (31.8%), diabetic nephropathyn 58 (24.6%), hypertensive nephrosclerosis in1 (13.1%), polycystic kidney disease in 125.1%), tubulointerstitial disease in 7 (3.0%),bstructive uropathy in 13 (5.5%), and not knownn 40 patients (16.9%).
Median plasma MPO level was 31.8 �g/L25th-75th percentiles, 24.4-42.7). Patients weretratified by tertiles of MPO, namely lower (MPO26.4 �g/L), middle (MPO of 26.4-37.7 �g/L),
nd upper tertiles (MPO �37.7 �g/L). Compari-ons across tertiles of plasma MPO are listed inable 1. Log2MPO showed no significant associa-
ion with use of �-blockers (P � 0.2), statinsP � 0.4), and angiotensin-converting enzymenhibitors/angiotensin receptor blockers (P � 0.4).sing bivariate partial correlation analysis control-
ing for other variables, log2MPO significantly cor-elated with CRP level (partial r � 0.224; P �.001), age (partial r � 0.185; P � 0.008), residualidney function (partial r � �0.164; P � 0.02),ale sex (partial r � �0.139; P � 0.05), and LVass index (partial r � �0.135; P � 0.05). Other
ariables, including diabetes, background athero-clerotic vascular disease, hemoglobin level, serum
lbumin level, low-density lipoprotein cholesterol
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evel, and duration of dialysis therapy had no signifi-ant correlation with log2MPO.
During follow-up, 69 patients died, 25 patientsnderwent kidney transplant, and 24 patientsere switched to long-term hemodialysis therapy.auses of death included 6 acute myocardial
schemic events, 12 strokes, 19 sudden cardiaceaths, 2 heart failure episodes, 4 peripheralascular diseases, 1 ventricular arrhythmia, 9eritonitis episodes, 11 other infections, 2 malig-ancies (carcinoma of lung and pancreas), and 3ialysis therapy terminations. Baseline median
Table 1. Base
Total (N � 236) Low
en/women 122:114
ge (y) 56 � 12
uration on dialysis (mo) 26 (15.0, 50.8) 23 (
iabetes mellitus 73 (30.9) 1
ositive smoking history 88 (37.3) 2
ackground AVD 55 (23.3) 1
ackground CAD 47 (19.9) 1
ackground HF 91 (38.6) 3
ody mass index (kg/m2) 23.1 � 3.4 2
ystolic BP (mm Hg) 147 � 17 1
iastolic BP (mm Hg) 82 � 10
emoglobin (g/dL) 9.22 � 1.71 9.
erum albumin (g/dL) 2.86 � 0.51 2.
a � P (mg2/dL2) 54 � 17
DL cholesterol (mg/dL) 128 � 39 1
DL cholesterol (mg/dL) 48 � 17
riglycerides (mg/dL) 183 � 129 1
lasma MPO (�g/L) 31.8 (24.4, 42.7) 23 (
-Reactive protein (mg/L) 2.66 (0.91, 8.23) 1.29
TnT (�g/L) 0.06 (0.01, 0.15) 0.03
T-pro-BNP (pg/mL) 5,842 (1,950, 18,335) 4,098 (
V mass index (g/m2) 224 � 84 2
V ejection fraction (%) 53 � 9 5
otal weekly Kt/V 1.81 � 0.46 1.
eritoneal dialysis Kt/V 1.52 � 0.36 1.
otal weekly CCr (L/wk/1.73 m2) 57 � 22
esidual GFR (mL/min/1.73 m2) 0.61 (0, 1.92) 0.9
Note: Continuous data expressed as mean � standardxpressed as number (percentage). Conversion factors fo/L, �10; Ca � P in mg2/dL2 to mmol2/L2, �0.0806; LDLg/dL to mmol/L, �0.02586; triglycerides in mg/dL to mmoAbbreviations; AVD, atherosclerotic vascular disease; B
oronary artery disease; CCr, creatinine clearance; cTigh-density lipoprotein; HF, heart failure; Kt/V, urea cleayeloperoxidase; NT-pro-BNP, N-terminal pro–brain natriu
lasma MPO level was significantly higher in t
atients who died versus those who survived the-year follow-up (35.6 [25th-75th percentiles,7.1-47.5] vs 29.1 �g/L [25th-75th percentiles,3.6-38.4], respectively; P � 0.002).Eighty-one patients experienced one or more
ardiovascular events. The first cardiovascularvent included 25 strokes, 25 acute myocardialschemic events, 6 peripheral vascular diseasevents, 10 sustained arrhythmias, and 15 suddenardiac deaths. Baseline median plasma MPOevel was significantly higher in patients whoad one or more cardiovascular events versus
haracteristics
Plasma MPO TertileP forTrend78) Middle (n � 80) Upper (n � 78)
38:42 35:43 0.05
56 � 11 58 � 10 0.008
.5) 35 (17.0, 63.3) 30 (18.0, 50.3) 0.006
) 26 (32.5) 28 (35.9) 0.3
) 34 (42.5) 25 (32.1) 0.4
) 21 (26.3) 19 (24.4) 0.6
) 16 (20.0) 16 (20.5) 0.9
) 32 (40.0) 26 (33.3) 0.5
0 23.1 � 3.3 23.5 � 3.7 0.2
148 � 16 146 � 18 0.8
82 � 9 82 � 10 0.6
1 9.11 � 1.67 9.35 � 1.77 0.7
1 2.85 � 0.59 2.86 � 0.43 0.9
55 � 19 52 � 13 0.4
131 � 41 125 � 40 0.6
48 � 18 47 � 17 0.5
186 � 127 202 � 162 0.1
.4) 31.8 (28.8, 33.3) 48 (42.7, 57.2) �0.001
.84) 3.14 (0.64, 6.33) 5.64 (2.03, 17.48) �0.001
.13) 0.07 (0.01, 0.16) 0.07 (0.01, 0.17) 0.2
4,336) 7,258 (2,672, 21,406) 5,380 (1,860, 20,192) 0.5
235 � 95 216 � 78 0.4
6 52.1 � 10.8 52.6 � 8.6 0.2
6 1.78 � 0.35 1.82 � 0.54 0.6
6 1.58 � 0.37 1.53 � 0.36 0.09
53 � 16 58 � 26 0.2
.4) 0.27 (0, 1.37) 0.15 (0, 1.98) 0.003
tion or median (25th, 75th percentiles); categorical datahemoglobin in g/dL to g/L, �10; serum albumin in g/dL toterol in mg/dL to mmol/L, �0.02586; HDL cholesterol in
.01129.d pressure; Ca � P, calcium-phosphorus product; CAD,
rdiac troponin T; GFR, glomerular filtration rate; HDL,; LDL, low-density lipoprotein; LV, left ventricular; MPO,eptide.
line C
er (n �
49:29
53 � 13
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9 (37.2
5 (19.2
5 (19.2
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47 � 17
83 � 11
20 � 1.7
87 � 0.5
54 � 19
26 � 35
50 � 15
60 � 83
20.3, 24
(0.67, 2
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22 � 79
4.6 � 7.
85 � 0.4
46 � 0.3
59 � 23
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Myeloperoxidase in Kidney Failure 941
ow-up (35.4 [25th-75th percentiles, 26.8-50.8]s 30.0 �g/L [25th-75th percentiles, 23.4-38.0];� 0.001).Figure 1A and B shows Kaplan-Meier esti-ates of overall survival and cardiovascular
vent–free survival probability of patients strati-ed by tertiles of plasma MPO. On univariatenalysis, HRs associated with doubling in plasmaPO level were 1.44 (95% confidence interval
CI], 1.08-1.91; P � 0.01) for all-cause mortalitynd 1.59 (95% CI, 1.21-2.08; P � 0.001) for firstardiovascular event. Table 2 lists the univariateox regression analysis for all-cause mortalitynd cardiovascular events and the associatedrea under the curve. Table 3 lists adjusted HRsssociated with log2MPO in relation to all-causeortality and first cardiovascular event in theultivariable Cox regression analysis. In pa-
ients without background atherosclerotic vascu-
Figure 1. Kaplan-Meier esti-ates of (A) overall survival prob-bility and (B) fatal or nonfatal car-iovascular event–free survivalrobability of patients stratified byertiles of plasma myeloperoxi-ase (MPO). Lower tertile, MPO26.4 �g/L; middle tertile; MPO,26.4 to �37.7 �g/L; upper ter-
ile, MPO �37.7 �g/L.
ar disease (n � 181), univariate HRs for dou- t
ling in plasma MPO level in relation to mortalitynd cardiovascular events were 1.51 (95% CI,.07-2.13; P � 0.02) and 1.70 (95% CI, 1.24-.34; P � 0.001), respectively. Adjusting forariables (with P � 0.05 on univariate analysis),Rs associated with doubling in plasma MPO
evel in relation to mortality and cardiovascularvent were 1.55 (95% CI, 1.03-2.35; P � 0.04) and.71 (95% CI, 1.19-2.47; P � 0.004), respectively.
The additional predictive value of log2MPOor mortality and cardiovascular events at 3ears was investigated using ROC curve anal-sis (Table 4). Areas under the curve for mor-ality and cardiovascular events were highesthen log2MPO was included in the model incor-orating CRP, cTnT, and NT-pro-BNP levels inddition to the standard clinical, demographic,iochemical, dialysis, and echocardiographic param-ters (model 4; Table 3). Figure 2A and B reports
he additional predictive power of log2MPO for
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ll-cause mortality and cardiovascular events usingtepwise multivariable Cox regression analysis.
DISCUSSION
This study is the first to show that plasmaPO level provides significant independent and
Table 2. Univariate Analysis of Factors in Rela
All-Cau
Variables HR (95% CI)
ge (/1 y) 1.06 (1.03-1.0
ale sex 1.42 (0.88-2.2
ositive smoking history 1.44 (0.90-2.3
iabetes 1.72 (1.07-2.7
ypertension 1.06 (0.54-2.0
ackground AVD 3.32 (2.05-5.3
ackground CAD 3.02 (1.85-4.9
ackground HF 2.32 (1.45-3.7
uration of dialysis (/1 mo) 1.01 (0.001-1.
esidual GFR (/1 mL/min/1.73 m2) 0.63 (0.49-0.8
emoglobin (/1 g/dL) 0.98 (0.85-1.1
erum albumin (/1 g/dL) 0.34 (0.21-0.5
a � P (/1 mg2/dL2) 1.01 (0.99-1.0
DL cholesterol (/1 mg/dL) 0.99 (0.98-1.0
V mass index (/1 g/m2) 1.006 (1.004-1.
-Reactive protein (/1 mg/L) 1.03 (1.02-1.0
TnT (/0.1 �g/L) 1.09 (1.05-1.1
T-pro-BNP (/1,000 pg/mL) 1.06 (1.04-1.0
og2MPO (/1 �g/L) 1.44 (1.08-1.9
Abbreviations: AVD, atherosclerotic vascular disease; CaTnT, cardiac troponin T; GFR, glomerular filtration rate; Cow-density lipoprotein; LV, left ventricular; MPO, myeloperox
Table 3. Unadjusted and Adjusted HRs for All-Cause MoStepwise Multivariab
Model Covariates
Univariate �
1 Age, sex, diabetes, background AVD, backgrosmoking, hypertension, LDL cholesterol
2 Model 1 � duration of dialysis � residual GFRserum albumin � hemoglobin � Ca � P �index
3 Model 2 � CRP
4 Model 3 � NT-pro-BNP � cTnT
Note: Log2MPO is equivalent to doubling in plasma MPOAbbreviations: AVD, atherosclerotic vascular disease; Ca-reactive protein; cTnT, cardiac troponin T; GFR, glom
ow-density lipoprotein; LV, left ventricular; MPO, myeloperoxidas
dditional predictive value for long-term mortal-ty and cardiovascular events beyond the stan-ard clinical, demographic, biochemical, dialy-is, and echocardiographic parameters, as well asRP, cTnT, and NT-pro-BNP levels, in patientsith ESRD on maintenance PD therapy. Despite
All-Cause Mortality and Cardiovascular Events
tality Cardiovascular Events
P HR (95% CI) P
�0.001 1.05 (1.03-1.07) �0.001
0.1 1.26 (0.81-1.95) 0.3
0.1 1.46 (0.94-2.26) 0.1
0.03 2.05 (1.32-3.19) 0.001
0.9 1.14 (0.60-2.15) 0.7
�0.001 3.23 (2.06-5.07) �0.001
�0.001 2.10 (1.30-3.39) 0.002
0.001 1.76 (1.14-2.73) 0.01
0.03 1.004 (1.00-1.01) 0.9
�0.001 0.78 (0.65-0.93) 0.004
0.7 0.85 (0.74-0.98) 0.03
�0.001 0.43 (0.27-0.68) �0.001
0.5 1.01 (1.00-1.02) 0.2
0.002 0.99 (0.99-1.00) 0.07
�0.001 1.006 (1.004-1.008) �0.001
�0.001 1.02 (1.01-1.04) �0.001
�0.001 1.13 (1.09-1.17) �0.001
�0.001 1.05 (1.03-1.07) �0.001
0.01 1.59 (1.21-2.08) 0.001
alcium-phosphorus product; CAD, coronary artery disease;fidence interval; HF, heart failure; HR, hazard ratio; LDL,T-pro-BNP, N-terminal pro–brain natriuretic peptide.
nd Cardiovascular Events Associated With Log2MPO, byRegression Models
All-Cause Mortality Cardiovascular Event
HR (95% CI) P HR (95% CI) P
1.44 (1.08-1.91) 0.01 1.59 (1.21-2.08) 0.001
F, 1.53 (1.10-2.11) 0.02 1.61 (1.19-2.19) 0.002
ss1.57 (1.14-2.17) 0.006 1.65 (1.22-2.22) 0.001
1.50 (1.07-2.10) 0.02 1.60 (1.17-2.18) 0.003
1.46 (1.02-2.08) 0.04 1.60 (1.17-2.18) 0.003
alcium-phosphorus product; CI, confidence interval; CRP,filtration rate; HR, hazard ratio; HF, heart failure; LDL,
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Myeloperoxidase in Kidney Failure 943
howing correlations with inflammation and re-idual kidney function, MPO level remainedrognostically significant in multivariable Coxegression models independent of residual kid-ey function and CRP, cTnT, and NT-pro-BNP
Figure 2. Incremental predic-ive value of log2MPO (doubling inlasma myeloperoxidase [MPO]
evel) for (A) all-cause mortalitynd (B) fatal or nonfatal cardiovas-ular event in the stepwise multi-ariable Cox regression analysis.A) The sequential addition of-reactive protein (CRP), cardiac
roponin T (cTnT), N-terminal pro–rain natriuretic peptide (NT-pro-NP), and log2MPO significantly
mproved the predictive power ofmodel including clinical (diabe-
es mellitus, background athero-clerotic vascular disease, posi-ive smoking history, hypertension,nd duration of dialysis therapy),emographic (age and sex), bio-hemical (hemoglobin, serum al-umin, calcium-phosphorus prod-ct, and low-density lipoproteinholesterol values), dialysis (re-idual glomerular filtration rate),nd echocardiographic parame-
ers (left ventricular mass index).B) The sequential addition ofTnT, NT-pro-BNP, and log2MPO,ut not CRP, values significantly
mproved the predictive power ofmodel including clinical, demo-
Table 4. Additional Predictive Value of Log2MPO aCardiova
Model
odel 1: clinical, demographic, biochemical, dialysis, andechocardiographic parameters
odel 2: model 1 � CRP
odel 3: model 2 � cTnT � NT-pro-BNP
odel 4: model 3 � log2MPO
Note: Data presented are based on ROC curve analyarentheses. Clinical and demographic parameters includeiochemical parameters include hemoglobin level, low-densarameters include duration of dialysis therapy and residuaentricular mass index. log2MPO is equivalent to a doublingAbbreviations: AUC, area under the curve; CRP, C-rea
ro–brain natriuretic peptide; MPO, myeloperoxidase; ROC
raphic, biochemical, dialysis, andchocardiographic parameters.
evels. Furthermore, MPO level had significantncremental predictive value in models incorpo-ating clinical, demographic, biochemical, dialy-is, and echocardiographic risk factors, as well asRP, cTnT, and NT-pro-BNP levels. Our obser-
er Cardiac Biomarkers in Predicting Mortality andEvents
All-Cause Mortality Cardiovascular Events
0.843 (0.783-0.903) 0.780 (0.724-0.853)
0.838 (0.778-0.898) 0.784 (0.719-0.849)
0.854 (0.797-0.912) 0.791 (0.725-0.857)
0.861 (0.804-0.918) 0.810 (0.764-0.874)
calculated AUCs or C statistics; 95% CIs are given iniabetes, and background atherosclerotic vascular disease;protein cholesterol level, and serum albumin level; dialysisrular filtration rate; the echocardiographic parameter is leftsma MPO level.rotein; cTnT, cardiac troponin T; NT-pro-BNP, N-terminalver operating characteristic.
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Wang et al944
ations extend a previous study linking plasmaPO level and mortality in hemodialysis pa-
ients17 and add value in providing new insightsnto the pathogenesis of increased cardiovascularortality in PD patients. Increased production ofPO-catalyzed 3-chlorotyrosine in dialysis pa-
ients has been related to increased oxidativetress,25 and 3-chlorotyrosine is present in hu-an atherosclerotic aorta.9 Increased plasmaPO levels during hemodialysis also appears to
eflect increased oxidative stress.26 Therefore,ncreased plasma MPO levels may contribute toncreased cardiovascular mortality in patientsith ESRD through leukocyte activation and
ncreased oxidative stress.Although MPO and CRP are both inflamma-
ory markers and are closely correlated in bothhe general and ESRD populations,17,27 in-reased plasma MPO levels may more specifi-ally reflect increased oxidative stress. In con-rast to CRP level, which remains increased for aong time, MPO has a much shorter half-life. Aeturn of MPO level to baseline was observedithin 1 week after acute coronary syndrome.13,28
hese data suggest that recruitment and degranu-ation of neutrophils with release of MPO likelys the primary event, followed by release of othernflammatory proteins, such as CRP.28 CRP levelay reflect vascular inflammation more, whereasPO may be more a systemic marker of neutro-
hil activation and plaque instability. Buffon etl29 showed widespread systemic activation ofeutrophils across the coronary vascular bed inatients with unstable angina independent of theite of culprit stenosis. Furthermore, systemicorrelation was found between CRP level andither aortic or coronary sinus neutrophil MPOevel.30 Thus, the role of CRP and MPO inredicting cardiovascular risk likely is comple-entary. No previous study has compared MPO
evels in hemodialysis and PD patients. How-ver, hemodialysis may induce more MPO acti-ation through leukocyte activation at the dialy-is membrane,29,31 and the degree of MPOctivation may be related to the biocompatibilityf dialyzer membranes.27 However, the inversessociation between plasma MPO level and re-idual kidney function in PD patients is notewor-hy. It is possible that this may be caused byncreased oxidative stress and inflammation with
orsening uremia. Human MPO is a 150-kDa cemoprotein,32 and its increase with decrease inesidual kidney function is unlikely to be ex-lained by decreased kidney clearance alone.dditional study is needed to clarify this issue
nd compare MPO levels between hemodialysisnd PD patients.
Both cTnT and NT-pro-BNP recently havemerged as useful biomarkers for prognostica-ion in patients with ESRD in that a cTnT levelncrease indicates subclinical myocardial necro-is, whereas an NT-pro-BNP level increase re-ects increased LV wall stress.33 Studies of PDatients also have shown their usefulness in pre-icting mortality and cardiovascular events.34,35
owever, in this study, plasma MPO level had noorrelation with cTnT or NT-pro-BNP level, sug-esting that MPO likely reflects a unique aspectf cardiovascular risk independent of cTnT andT-pro-BNP. A previous study showed the stabil-
ty of plasma MPO levels over time in theeneral population.12 Whether similar stability isbserved in the ESRD population requires fur-her evaluation.
Multiple lines of experimental evidence sug-est that MPO is proatherogenic, has powerfulxidative capacity, and contributes to inflamma-ory tissue injury.2-6 MPO has been linked to theevelopment of atherosclerotic plaque, plaquenstability,36,37 and production of oxidized lip-ds,38,39 all pivotal steps in atherosclerosis. Expres-ion of human MPO in murine macrophagesncreased atherosclerosis in hypercholesterolemic
ice.40 There also is clinical evidence to supportn important link between MPO and cardiovascu-ar disease in humans. Patients with MPO defi-iency were protected against cardiovascular dis-ase.41 A single plasma MPO measurementredicts future risk of coronary artery disease inpparently healthy individuals42 and early risk ofyocardial infarction and risk of major adverse
ardiac events in patients presenting to the emer-ency department with chest pain independent ofevels of CRP and other inflammatory markers.41
ncreased leukocyte and blood MPO levels alsoorrelated with angiographically proven coro-ary artery disease independent of CRP level andramingham risk score.12 Our findings thereforere consistent with previous studies of the gen-ral population and support the hypothesis thatPO has a significant contribution to increased
ardiovascular mortality independent of CRP.
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Myeloperoxidase in Kidney Failure 945
lthough increased plasma MPO level predictsn increased risk of cardiovascular events andortality over the long-term in PD patients, we
id not observe a direct cross-sectional link be-ween plasma MPO level and atheroscleroticascular disease. This may seem contrary to ourypothesis. A previous study of the general popu-ation showed that increased plasma MPO levelreceded the onset of coronary artery disease byears.42
Our study has several limitations. First, plasmaPO and other parameters were measured on a
ingle occasion and did not reflect possiblehanges with time on dialysis therapy. However,iven that this is a prognostic rather than etio-ogic study, a single time measurement also repro-uces the typical situation of daily clinical prac-ice. Second, our study included prevalent dialysisatients and may introduce survival bias. Furthertudy is needed to elucidate the exact mechanis-ic link between MPO level and cardiovascularisease in uremia. In this study, the rule of 10vents per variable in the multivariable Coxegression analysis was relaxed to show ad-quate control of confounding43; however, wecknowledged that the models may be somewhatverfitted.In conclusion, our study has shown that plasmaPO level predicts long-term mortality and car-
iovascular events in patients with ESRD be-ond the standard clinical, dialysis, echocardio-raphic, and biochemical parameters, includingRP, cTnT, and NT-pro-BNP levels. MPO maye involved in the pathogenesis of increasedardiovascular mortality in PD patients.
ACKNOWLEDGEMENTSThis study was presented as a free communication in
enal Week of the American Society of Nephrology, Novem-er 4-9, 2008, Philadelphia, PA.Support: This study was supported by Hong Kong Health
ervice Research Grant No. 6901023, of which Dr Wang ishe principal investigator.
Financial Disclosure: The authors declare that they haveo relevant financial interests.
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