Plasma Pro-Adrenomedullin But Not Plasma Pro-Endothelin Predicts Survival in Exacerbations of COPD

Original Research COPD

Plasma Pro-Adrenomedullin But Not Plasma Pro-Endothelin Predicts Survival in Exacerbations of COPD* Daiana Stolx, MD; Mirjam Christ-Crain, MD; Nils G. Morgenthaler, MD; David Miedinger, MD; Jorg Leuppi, MD; Christian Miiller, MD; Roland Bingisser, MD, FCCP; Joachim Struck, MD; Beat Miiller, MD; and Michael Tamm, MD, FCCP

Background: Plasma endothelin and adrenomedullin are increased in patients with pulmonary arterial hypertension, hypoxia, and pulmonary infections, conditions that predict survival in patients with COPD. We investigated whether plasma pro-endothelin-1 (proET-1) and/or pro-adrenomedullin (proADM) on admission to the hospital for acute exacerbation predict survival in patients with COPD. Methods: We examined 167 patients who had been admitted to the hospital for acute exacerbation, and we followed them up for 2 years. We measured plasma C-terminal (CT) proET-1 and mid-regional (MR) proADM on hospital admission, after 14 to 18 days, and after 6 months. In addition to plasma CT proET-1 and MR proADM, we assessed with Cox regression univariate and multivariate analyses the predictive value of clinical, functional, and laboratory parameters on 2-year survival. We analyzed the time to death by Kaplan-Meier curves. ResuZts: Compared to recovery and stable state, CT-proET-1and MR-proADM were significantly increased on hospital admission (p < 0.001 and p = 0.002, respectively). MR-proADM, but not CT-proET-1, was associated with increased in-hospital mortality (p = 0.049) and independently predicted 2-year survival (p = 0.017). ProADM plasma levels > 0.84 nmoVL on hospital admission increased the mortality risk within 2 years from 13to 32% (p = 0.004).By contrast, age (p = 0.779), Charlson comorbidity score (p = 0.971), body mass index (p = 0.802), FEV, percent predicted (p = 0.741), PAo, (p = 0.744), PAco, (p = 0.284), leukocyte counts (p = 0.333), C-reactive protein (p = 0.772), procalcitonin (p = 0.069), pulmonary arterial hypertension (p = 0.971), and CT-proET-1(p = 0.223) were not independently associated with 2-year survival. Conclusions: This study shows that plasma proADM but not plasma proET-1 on admission to the hospital for acute exacerbation independently predicts survival, thus suggesting that this biomarker could be used to predict prognosis in patients with COPD. (CHEST 2008; 134:263-272) Key words: biomarker; chronic bronchitis; hospitalization; prognosis Abbreviations: BMI = body mass index; CT = C-terminal; ET-1 = endothelin-1; GOLD = Global Initiative for Chronic Obstructive Lung Disease; IQR = interquartile range; MR = mid-regional; proADM = pro-adrenomedullin; proET-l = pro-endotbelin-1

c

OPD is a growing cause of morbidity and mortality.l.2 Exacerbations of COPD impose an increasingly large burden on health services throughout the world and are now being recognized as important events in disease progres~ion.~,~ The levels of several circulating biomarkers are increased during exacerbations, potentially reflecting the spillover of local airway inflammation into the circulation?8 www.chestjournal.org

Systemic markers have gained general interest as means of determining disease severity and prognosis in stable COPD.y-ll However, there is little information about whether or not biomarker levels can predict clinical outcomes in the setting of exacerbations.12 Severe acute exacerbations of COPD (ie, those requiring hospital admission) have an important impact on patient prognosis, including mortality, CHEST I 134 1 2 / AUGUST, 2008

263

dial infarction and systemic inflammatory response and generate great health-care burdens and economic syndrome. Furthermore, adrenomedullin levels are costs.1z16 Because some patients might present for increased in patients with pulmonary arterial hyperthe first time to the hospital due to an exacerbation, tension and end-stage pulmonary disease.33 The a biomarker allowing risk stratification in this particprognostic value of proET-1 has not yet been evalular setting could be of special interest. uated. However, pulmonary arterial hypertension, Endothelin-1 (ET-1) is a potent vasoconstrictive which is associated with increased ET-1 plasma peptide that is derived from the vascular endothelevels, is linked to worse clinical outcome in COPD lium, which has been classically related to the pathopatients.337 Therefore, we have investigated whether genesis of pulmonary arterial hypertension. 17,18The plasma proADM and/or proET-1 levels on hospital synthesis of ET-1 is inducible by various factors, admission predict survival in a well-characterized coincluding hypoxia and pulmonary infections.19-21 It is hort of patients with acute exacerbations of COPD. also thought to have important proinflammatoryeffects The primary end point was 2-year survival. The secin the airways, being both a chemoattractant and an ondary end points were in-hospital mortality and length up-regulator of other inflammatory mediators.22 of hospital stay. Adrenomedullin, a peptide with 52 amino acids, has immune-modulating, metabolic, and vascular actions.23 It can behave both as a hormone and a cytokine, and can simultaneously control pulmonary MATERIALS AND METHODS blood flow, leukocyte migration, and electrolyte bala n ~ e . 2 Adrenomedullin ~~5 also possesses antimicroSetting and Study Population bial properties, having a direct bactericidal activity This prospective cohort study took advantage of baseline data that is further enhanced by the modulation of comfrom 167 patients with acute exacerbations of COPD, who were plement activity.26 admitted to the emergency department of the University HospiET-1 and adrenomedullin are rapidly cleared from tal Basel and were included in a prospective, randomized trial.8 A the circulation, and therefore are difficult to measure. predefined secondary end point was the assessment of further biomarkers in COPD patients3*30 Mid-regional (MR) pro-adrenomedullin (proADM) The diagnosis of COPD was based on clinical history, physical and C-terminal (CT) pro-endothelin-1 (proET-1) examination findings, and spirometric criteria according to the have been identified as more stable, in vivo precurGlobal Initiative for Chronic Obstructive Lung Disease (GOLD) sors of the mature molecules, reflecting directly the guidelines.40 An exacerbation of COPD was defined as “a suslevels of the rapidly degraded active adrenomedullin tained worsening of the patient’s condition, from the stable state and beyond normal day-to-day variations, that is acute in onset and ET- 1.27.28 necessitates a change in regular medication in a patient with ProADM plasma concentrations have been s ~ o w I Pand -~ ~ underlying COPD.”41Spirometry confirming the COPD diagnoto predict prognosis in patients with acute myocarsis was performed within 48 h of study inclusion. *From the Clinic of Pneumology and Pulmonary Cell Research (Drs. Stolz, Miedinger, Leuppi, and Tamm), the Clinic of Endocri, Diabetes, and Clinical Nutrition (Dr. Christ-Crain and B. and the Department of Internal Medicine (Drs. C. Miiller and Bingisser), University Hos ital Basel, Basel, Switzerland; and the Research Department &s. Morgenthaler and Struck), BRAHMS AG, Biotechnology Centre, Hennigsdorf, Germany. Dr. Stolz was partially supported by grants from the Swiss National Foundation and the Margarete and Walter Lichtenstein Foundation. Dr. Stolz has received speakers’ honoraria from BRAHMS AG (the manufacturer of proADM, pro-endothelin, and procalcitonin assays). Drs. Miiller, Miiller, and Christ-Crain served as consultants and were sponsored by BRAHMS AG for attending advisory board meetin s, speaking engagements, and research. Drs. Morgenthaler an$ Struck are employees of BRAHMS AG. Drs. Christ-Cain, Miedinger, Leuppi, Bingisser, and Tamm have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article. Manuscript received January 15, 2008; revision accepted March 29, 2008. Reproduction of this article is rohibited without written permission from the American College ofchest Physicians (www.chestjoumal. orgmisdre rints shtml). Corresponkke io: Daiana Stolz, MD, Clinic of Pneumology, University Hos ital Basel, Petemgraben 4, CH-4031 Basel, Switzerland; e-mui~stolzd@~hbs.ch DOI: 10.1378/chest.08-0047

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Patients were excluded from the study if they were severely immunocompromised, or had asthma or cystic fibrosis. Patients were examined on admission to the emergency department by a resident who was supervised by a board-certified specialist in internal medicine. The baseline assessment included the gathering of clinical data and the performance of routine blood tests. Blood sampling for proADM and proET-1 determination was performed immediately after admission to the emergency department, concomitantlywith the routine blood sampling, and before the administration of any drug therapy. Spontaneously, expectorated sputum samples were obtained and examined by using standard techniques.42 Spirometry was performed by trained lung function technicians according to American Thoracic Society guideline^.^^ Respiratory symptoms were quantified using a questionnaire for patients with respiratory illnesses (range, 0 to 95; higher scores indicate greater discomfort).44 Historical data on echocardiography, performed within 6 months of the hospital stay, were obtained from hospital medical records. Relevant pulmonary arterial hypertension was defined as an estimated systolic pulmonary arterial pressure of > 35 mm Hg, as measured by e~hocardiography.~5 Follow-up visits comprising clinical, laboratory, and lung function and/or radiologic assessments were performed after 14 to 18 days and after 6 months following hospital admission. Thus, blood samples were collected on admission to the emergency department (ie,admission), after 14 to 18 days (ie, recovery phase) and after 6 months (ie, stable phase) following hospital admission. Original Research

The trial was approved by the Basel Ethics Committee and was regstered with the Current Controlled Trials Database (ISRCTN77261143).* AU participants gave written informed consent.

two tailed; p < 0.05 was defined as being significant. The data were analyzed using a statistical software package (SPSS, version 15 for Windows; SPSS Inc; Chicago IL; and Sigmaplot, version 10 for Windows; SYSTAT; San Jose, CA).

Olltcom All patients were followed up for a mean ( 2 SD) duration of

28.4 2 5.0 months. Patients who survived until follow-up were categorized as survivors, whereas patients who died within the follow-up period were categorized as nonsurvivors. The cause of death was adjudicated based on the review of medical records (from the University Hospital Basel, neighborhood institutions, nursing homes, day-care centers, emergency medical services, and family physicians) and personal interviews with attending physicians and family physicians. Medical records review was performed by two independent, board-certified pulmonary specialists. Discrepancies were settled by consensus. Vital status was additionally confirmed by family physicians and/or health insurance companies.

Measurements of CT-ProET-I, MR-ProADM, and Other k b o r a t o y Parameters MR-proADM was detected in the plasma of all patients with a new sandwich immunoassay (MR-proADM LIA; BRAHMS AG; Hennigsdorf, Germany).47The lowe? detection limit of the assay is 0.08 nmoVL, and the functional assay sensitivity is 0.12 nmoVL. CT-proET-1 levels were measured in plasma with another sandwich immunoassay (CT-proET-1 LIA; BRAHMS AG).2H The assay (mean reference range, 44.3 ? 10.6 pmoVL) has an analytical detection limit of 0.4 pmoVL. C-reactive protein levels were measured in ethylenediaminetetraacetic acid plasma (Hitachi Instrument 917; Roche Diagnostics; Rotkreuz, Switzerland). Procalcitonin levels were measured using 20 to 50 p L of plasma or serum by a time-resolved amplified cryptate emission technology assay (PCT KRYPTOR; BRAHMS AG). The assay has a functional assay sensitivity of 0.06 pg/L, 3-fold to 10-fold above normal mean values.

Statistical Analysis Discrete variables are expressed as counts (percentages), and continuous variables are expressed as the mean t- SD or median (interquartile range [IQR]). The comparability of groups was analyzed by x2 test or Fisher exact test, as appropriate. For paired, longitudinal analyses, the Wilcoxon test (two samples) and the Friedman test (multiple samples) were applied. For independent samples, the Mann-Whitney U test was used. To analyze the relationship between different variables and proADM and proET-1 levels on emergency department admission, a multiple linear regression model including age, Charlson condition and age-related score, body mass index (BMI), FEV, percent predicted, PO,, Pco,, leukocyte counts, C-reactive protein levels, procalcitonin levels, and the presence of pulmonary arterial hypertension was used. To assess the influence of proADM and proET-1 levels, age, Charlson condition and age-related score, BMI, FEV, percent predicted, PO,, Pco,, leukocyte counts, C-reactive protein, procalcitonin, the presence of pulmonary arterial hypertension, and comorbidities on %year survival, Coxregression univariate and multivariate analyses were performed. Correlation analyses were performed using the Spearman rank correlation. The time to death up to 2 years in patients with proADM levels below the median (< 0.84 nmol/L) and above the median ( 20.84 nmoVL) was analyzed by Kaplan-Meier survival curves and compared by log-rank tests. Skewed data were logarithmically transformed for regression analyses. All tests were www.chestjournal.org

RESULTS

The detailed baseline characteristics of the 167 patients are presented in Table l. Overall, 116 patients (69.5%) had relevant comorbidities. Sputum cultures grew bacterial pathogens in 65 cases (38.9%). Echocardiography results were available for 123 patients (73.7%). A total of 38 patients (22.8.%) demonstrated clinically relevant pulmonary arterial hypertension.45 In 12 cases (7.2%), echocardiography showed decreased left ventricular ejection fraction (ejection fraction, 5 40%). The median length of hospital stay was 9 days (IQR, 1to 15 days). Sixteen patients (9.6%) required intensive care. The in-hospital mortality rate was 3.0% (five patients). There were another 32 deaths during the follow-up period. Hence, a total of 37 patients (22.2%) died within 2 years of the initial hospitalization. The main causes of mortality were respiratory conditions (ie,COPD-related respiratory failure including pneumonia) in 19 patients and cardiovascular disorders in 12 patients. In one patient, the cause of death was unknown. Of the 37 patients who died during the 2-year follow-up period, 10 (27%) had concomitant malignancy (bronchial carcinoma, 5 patients; prostate carcinoma, 2 patients; urogenital carcinoma, 1 patient; peritoneal carcinomatosis, 1patient; and carcinoma of unknown primary site, 1 patient). In five cases, death was definitively attributed to a cause other than COPDrelated respiratory failure or cardiovascular disease (bronchial carcinoma, one case; colon diverticulitis, two cases; ischemic colitis, one case; and Staphylococcus aureus endocarditis, one case). In considering patients with concomitant comorbidities, we did not find an association between 2-year survival and cardiopathy (p = 0.119), pulmonary arterial hypertension (p = 0.348), diabetes mellitus (p = 0.293), and renal failure (p = 0.081). Likewise, the association between left ventricular failure and mortality at 2 years was not statistically significant (8% [l of 13 patients] vs 26% [29 of 110 patients], respectively; p = 0.138). In contrast, patients with malignancy (n = 24) had a significantly higher mortality compared to those without malignancy (n = 143; p = 0.013). Mortality at 2 years was similar across GOLD stages (stage IV, 13 of 40 patients; stage 111, 15 of 76 patients; stage 11, 15 of 76 patients; and stage I, 2 of 14 patients; p = 0.333). Seventy-three patients (43.7%) required a rehospitalization due to exacerbation within 2 years of CHEST I 134 I 2 I AUGUST, 2008

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Table 1-Baseline Characteristics of 167 Patients Presenting With an Acute Exacerbation of COPD* Characteristics Gender Male Female Age,+ yr BMI Smoking,$ pack-yr Duration of COPD,$ mo AECOPD hospitalization in previous year AECOPD hospitalization in previous year$ Duration of AECOPD, d Cough Increased sputum production Discolored sputum Dyspnea Fever Comorbidities Cardiopathy Arterial hypertension Malignancy Diabetes mellitus Renal failure Type of AECOPD (anthonisen criteria) 1 (t dyspnea, sputum purulence, sputum volume) 2 (two of the above) 3 (one of the above and one or more minor findings) GOLD stage I (FEV, 5 80% predicted) I1 (50% pred 5 FEV, 2 50% predicted and 5 80% predicted) 111 (FEV, 5 30% predicted and 2 50%predicted) IV (FEV, 5 30% predicted) Charlson weighted index of comorbiditiest Charlson condition and age-related scoret Estimated 10-yr survival rate,+ % FEVIP L % predicted Pao,,$ mm Hg Pace,,$ mm Hg Leukocyte counts,$ x lo9 cells/L

Values 75 (44.9) 92 (55.1) 70 (42-91) 24.6 (4.8) 45 (30-60) 127 (86) 82 (49.1) 0.98 (1.3) 4 (3-7) 142 (85) 113 (67.7) 95 (56.9) 155 (92.8) 68 (40.7)

I

I

T

I

Recovety phase

Stable phasr

76 (45.5) 42 (25.1) 24 (14.4) 19 (11.4) 15 (9.0) 80 (47.9) 36 (21.6) 51 (30.5)

Adrnisei on

I.*

14 (8.4) 37 (22.2)

I

I

I

Recove& phase

Stable'phacre

76 (45.5) 40 (24.0) 2 (14) 5 (4-7) 21 (0-53) 0.892 (0.397) 39.9 (16.9) 62.9 (15.7) 43.8 (11.0) 11.27(4.7)

*Values are given as No. (%), unless otherwise indicated. Lung function values represent results obtained during the recovery phase, all other characteristics were assessed on admission. AECOPD = acute exacerbation of COPD; = increase. +Valuesare given as No. (range). $Values are given as the median (IQR). $Values are given as the mean (SD).

follow-up. Among recurrent patients, the median time to readmission to the hospital was 174 days (IQR, 42 to 395 days).

CT-ProET-1 and MR-ProADM Plasma Levels on Hospital Admission, Recovey,and Stable Phase Circulating proET-1 and proADM levels on hospital admission, in the recovery phase, and in the 266

stable phase are shown in Figure 1. Compared to the recovery and stable phase, proADM and proET-1 levels were significantly elevated at hospitalization (p = 0.002 and p < 0.001, respectively). ProADM levels in the recovery phase and in the stable phase were similar (p = 0.350),while proET-1 concentrations in the recovery phase were lower than in the stable phase (p = 0.001).Compared to healthy individuals (mean, 0.33 nmol/L; SD, 0.07 n m ~ l / L ) , ~ '

__

Admission

FIGURE1. Top, A: proET-l levels on hospital admission (n = 167), in the recovery phase (14 to 18 days after hospital admission; n = 156), and in the stable phase (6 months after hospital admission; n = 144). At hospital admission, proET-1 levels were significantly increased (70.9 pmoVL; IQR, 53.7 to 103.0 pmoVL) compared to those in the recovery phase (58.0 pmoVL; IQR, 48.2 to 76.6 pmoVL) and the stable phase (61.6 m o m ; IQR, 51.3 to 83.0 pmoVL). * = p < 0.0001 comparing i v e l s on hospital admission vs recovery hase vs stable phase (Friedman test). Levels at the recovery !as, were lower than those in the stable phase (p = 0.001). e bars represent SEs. Bottom, B : proADM levels on hospital admission (n = 167), in the recovery phase (14 to 18 days after hospital admission; n = 156), and in the stable hase (6 months after hospital admission; n = 144). At hospitafadmission, proADM levels were significantly increased (0.84 nmoVL; IQR, 0.59 to 1.22 nmoVL) com ared to the recovery hase (0 72 nmoVL; IQR, 0.55 to 0.98 nmotL) and the stable p i a x (0.66 nmoVL; IQR, 0.49 to 0.95 nmoL'L). * = p = 0.002 corn aring levels on hos ital admission vs recovery phase vs stable pcase (Friedman testfl Levels at the recovery phase and stable phase were similar (p = 0.350). The bars represent SEs. Original Research

proADM levels were increased in 163 patients (97.6%) at exacerbation; 140 patients (89%) in the recovery phase of the disease and 114 patients (79.2%) in the stable phase of the disease. Similarly, compared to healthy individuals the mean proET-1 values (44.3 pmoVL; range, 10.5 to 77.4 pmoVL)28 were increased in 146 patients (87.4%) at exacerbation; 121 patients (77.6%) in the recovery phase of the disease and 102 patients (70.8%) in the stable phase of the disease. We found no correlation between COPD severity according to the GOLD criteria, and proET-1 and proADM levels at hospital admission (r = -0.078, p = 0.322; and r = -0.066, p = 0.406, respectively). ProADM and proET-1 levels were similar in patients with GOLD stage I disease (0.76 nmoVL [range, 0.55 to 0.981 and 72.4 pmoVL [range, 47.3 to 108 pmoVL], respectively), patients with GOLD stage I1 disease (0.97 nmoVL [range, 0.65 to 1.22 nmoVL] and 76 p m o a [62.5-1121, respectively), GOLD stage 111 disease (0.85 nmoVL [range, 0.59 to 1.33 nmoVL] and 69 pmoVL [range, 54.0 to 99.91, respectively), and GOLD stage IV disease (0.74 nmoVL [range, 0.51 to 1.14 nmoVL] and 70.4 pmoVL [range, 47.2 to 95.1 pmoVL], respectively; p = 0.372 and p = 0.600, respectively). ProET-1 and proADM levels did not discriminate between Anthonisen exacerbation types (p = 0.756) or between sputum bacterid growth results (p = 0.470). ProADM and proET-1 levels were similar in patients with and without previous antibiotic therapy on hospital admission (p = 0.703 and p = 0.085, respectively). Antibiotic therapy during hospitalization did not influence proADM and proET-1 levels at 14 to 18 days after hospitalization (p = 0.606 and p = 0.118, respectively). Similarly, there were no differences in proADM and proET-1 levels at 14 to 18 days after hospitalization in patients receiving steroids during hospitalization (0.720 nmol/L [range, 0.548 to 0.985 nmoyL] and 57.7 pmoK [range, 48.1 to 74.2 pmoK], respectively; n = 147) and in those who did not receive steroids (0.657 nmoVL [range, 0.560 to 0.870 nmoVL] and 62.7 p m o L [range, 52.2 to 80.9 pmoK], respectively; n = 20; p = 0.767 and p = 0.544, respectively). Conversely, proADM levels were significantly higher in patients with malignancy compared to those patients without malignancy (1.225 nmoVL [range, 0.718 to 1.770 nmoVL] vs 0.810 nmoVL [range, 0.571 to 1.100 nmoVL], respectively; p = 0.008). The respective values for proET-1 were 86.5 pmoyL [range, 69.7 to 1-50.5pmoVL] vs 66.9 pmoVL [range, 49.9 to 94.7 pmoVL], respectively; p = 0.003). Spearman correlation coefficients for patient characteristics on hospital admission and proET-1 and proADM levels on hospital admission are shown in Table 2. ProADM and proET-1 levels on hospital www.chestjournal.org

Table 2-Spearman

Correlation Between Clinical and Laboratory Markers, Plasma CT-proET-1, and MR-proADM (n = 167) on Hospital Admission ProET-1

ProADM

I

Parameters

I

p -Coefficient p Value 'p -Coefficient p ~ a l u e i

Age Cliarlson comorbidity score

0.179 0.367

< 0.001*

0.451 0.606

< 0.001* < 0.001*

BMI

0.107 0.077

0.179 0.329

0.116 0.024

0.143 0.761

0.033 0.023 0.103 0.239 0.395

0.712 0.798 0.188 0.002* < 0.001*

0.024 0.010 0.045 0.233 0.497 0.590

0.790 0.910 0.568 0.002* < 0.001* < 0.001*

0.590

< 0.001*

FEV, 9% predicted Pao, Paco, Leukocyte counts C-reactive protein Procalcitonin ProET-1 ProADM

0.021*

*Statistically significant

admission correlated significantly with age, Charlson comorbidity score, C-reactive protein level, procalcitonin level, and with each other. In our multivariate linear regression model, procalcitonin level (p = 0.026) and age (p = 0.033) were independent predictors of proET-1 levels on hospital admission (adjusted R2 = 0.189). The predictors for proADM level on hospital admission were age (p = 0.004), procalcitonin levels (p = O.OlS), and Pao, (p = 0.034; adjusted R2 = 0.237).

CT-ProET-1 and MR-ProADM and Pulmona y Arterial Hypertension ProET-1 and proADM levels tended to be higher in patients with pulmonary arterial hypertension compared to those with normal pulmonary pressures (Fig 2). ProET-1 and proADM levels in patients with and without impaired left ventricular ejection fraction (< 40%) were similar (p = 0.536 andp = 0.115, respectively). However, proADM levels but not proET-1 levels correlated significantly with left ventricular ejection fraction ( r = -0.222, p = 0.014; and r = -0.056, p = 0.539, respectively).

CT-ProET-1 and MR-ProADM and In-Hospital Mortality ProET-1 levels correlated with the length of hospital stay ( r = 0.165; p = 0.033) but not with length of ICU stay ( r = 0.105; p = 0.177). Patients transferred to the ICU and those who were not admitted to the ICU had similar proET-1 levels on hospital admission (72.6 pmoVL [range, 59.4 to 169.8 pmoVL] vs 70.1 pmoVL [range, 53.6 to 95.5 pmoVL], respectively; p = 0.221). There were no differences CHEST I 134 I 2 I AUGUST, 2008

267

A

nmow; range, 0.58 to 1.22 nmom; p = 0.049). Hospital stay was longer in patients with high proADM levels (11days; IQR, 7 to 16 days) compared to those hospitalized with low proADM levels (8 days; IQR, 1to 15 days; p = 0.030).

250

p = 0.054

CT-ProET-1 and MR-ProADM, and 2-Year Survival

I

OJ

No PAH

BZ5 20

PAH

p = 0.031 0

T

s15 r

ie,, P

05

00

No PAH

PAH

FIGURE2. Top, A: mean proET-1 plasma levels on hospital admission were similar in patients with pulmonary arterial hypertension (81.0 prnoVL; range, 64.5 to 148.8 pmoVL; n = 28) corn ared to patients with normal pulmonary pressures (71.2 p m o k ; range, 55.0 to 91.7 pmoVL; n = 95; p = 0.054 [MannWhitney U test]). The shaded areas represent the 25th to 75th IQRs. Outliers (5tW95th percentiles) are denoted by the circles. Bottom, B: mean proADM plasma levels on hospital admission were significantly higher in patients with pulmonary arterial hypertension (1.06 nmoVL; range, 0.76 to 1.63 nmoVL; n = 28) com ared to patients with normal pulmonary pressures (0.82 nmo5L: range, 0.61 to 1.23 nmoVL; n = 95; p = 0.031 [MannWhitney U test]). The shaded areas represent the 25th to 75th IQRs. Outliers (5tW95th percentiles) are denoted by circles. PAH = pulmonary artery hypertension.

in proET-1 levels in patients who survived (70.5 moVL; range, 53.7 to 103.0 moVL) and those who died (71.6 pmoVL; range, 54.8 to 132.5 pmoVL) during hospitalization (p = 0.714). ProADM levels on hospital admission correlated with the length of hospital stay (r = 0.274; p < 0.0001) and tended to correlate with the length of ICU stay ( r = 0.151; p = 0.051). Patients requiring ICU stay had higher proADM levels (1.23 nmoVL; range, 0.61 to 2.14 nmoVL) than those who did not require ICU admission (0.83 nmoVL; range, 0.59 to 1.14 nmoVL; p = 0.057). Circulating levels in hospital nonsurvivors (1.07 nmoVL; range, 0.95 to 2.80 nmoVL) were significantly higher than in hospital survivors (0.82 268

Circulating proADM levels on hospital admission were significantly higher in long-term nonsurvivors compared to long-term survivors (1.14 nmoVL [range, 0.80 to 1.56 nmoVL] vs 0.76 nmoVL [range, 0.55 to 1.05 nmoVL], respectively; p < 0.0001). The corresponding values for proET-1 levels were 91.1 pmoVL (range, 63.5 to 127.0 pmoVL) and 67.5 pmol/L (range, 49.7 to 87.1 pmol/L; p = 0.007). Using a univariate logistic model and a Cox regression model, we evaluated the prognostic value of proADM levels, proET-1 levels, age, and clinical parameters to predict 2-year survival following hospitalization for acute exacerbation (Table 3). Age, Charlson comorbidity score, PAco,, procalcitonin levels, proET-1 levels, and proADM levels on hospital admission were significantly associated with 2-year survival, while no association was found for BMI, PAo,, leukocyte counts, C-reactive protein levels, FEV, percent predicted, and the presence of pulmonary arterial hypertension. Compared to survivors, nonsurvivors were slightly older (mean age, 75 years [age IQR, 59 to 91 years] vs 70 years [age IQR, 42 to 88 years], respectively; p = 0.068), had higher mean carbon dioxide arterial content (51.8 mm Hg [SD, 16.4 mm Hg] vs 42.2 mm Hg [SD, 7.7 mm Hg], respectively; p = 0.008), and a higher mean Charlson comorbidity score (7 [range, 6 to 8.51 vs 4.5 [range, 3 to 71, respectively; p < 0.001). In the multivariate Cox regression model analysis, proADM level was the only predictive factor independently associated with 2-year survival (p = 0.017) [Table 41. Using the best diagnostic cutoff value for proADM level (0.77 nmoVL), the sensitivity and specificity of proADM level to predict death at 2 years were 0.81 (95% CI, 0.68 to 0.90) and 0.53 (95% CI, 0.49 to 0.56), respectively. At this cutoff value, the numberneeded-to-diagnose in this study (ie,the number of patients who had to be tested to identify a nonsurvivor at 2 years) was 3 (95% CI, 2 to 6). Using the best diagnostic cutoff value (85.7 pmoVL), the sensitivity and specificity of proET-1 level to predict death at 2 years were 0.54 (95% CI, 0.40 to 0.67) and 0.75 (95% CI, 0.71 to 0.78), respectively. Kaplan-Meier survival curves showing patients with circulating levels of proADM below the median (<0.84 nmol/L) or above the median (20.84 nmoVL) on hospital admission are shown in Figure 3. ProADM plasma levels 2 0.84 nmoVL on hospital admission Original Research

Table 3-Univahte Logistic Regression and Cox Regression Analyses for the Association Between Clinical and Laboratory Parameters on Hospital Admission and 2-Year Mortality in COPD Patients (n = 167) Logistic Regression I

p Value

Odds Ratio (95% CI)

Parameters

1.046 (1.004-1.090) 1.473 (1.2461.740) 0.958 (0.884-1.037) 0.268 (0.040-1.786) 31.15 (4.52-214.45) 0.690 (0.258-1.846) 1.126 (0.878-1.444) 1.780 (1.195-2.653) 2.491 (1.164-5.332) 3.978 (1.840-8.599) 0.983 (0.961-1.004) 0.807 (0.29W2.225)

Age Charlson comorbidity score BMI Pao, Paco, Leukocyte counts C-reactive protein Procalcitonin ProET-l ProADM FEV, % predicted Pulmonary arterial hypertension*

Cox Regression I

0.031t

< 0.001t 0.289 0.174 < o.oo1t 0.460 0.349 0.005t O.Ol9.i < 0.001t 0.117 0.678

I

p Value

Hazard Ratio (95% CI)

1.043(1.006-1.081) 1.270 (1.1561.395) 0.966 (0.901-1.035) 0.276 (0.049-1.564) 22.59 (5.30-96.36) 0.709 (0.303-1.662) 1.094 (0.881-1.3599 1.517 (1.144-2.010) 2.189 (1.178-4.066) 3.155 (1.779-5.596) 0.985 (0.9661.005) 1.103 (0.451-2.698)

I

0.024t

< o.oo1t 0.321 0.146 < 0.001t 0.429 0.415 0.004t 0.013t < 0.001t 0.141 0.831

*n = 123. t Statistically significant.

increased the mortality risk within 2 years of hospitalization from 13 to 32% (p = 0.004). Compared to patients with proADM levels of < 0.84 nmoVL, the odds ratio for mortality within 2 years in patients presenting with proADM levels 2 0.84 nmoYL at hospital admission was 3.12 (95% CI, 1.35 to 7.58). Thus, one in every six patients (95% CI, 3.2 to 15.9) with proADM levels on hospital admission above the median died within 2 years of hospitalization for acute exacerbation.

DISCUSSION In this investigation, we have examined the predictive value of plasma proET-1 and proADM levels

on survival in patients with acute exacerbations of COPD requiring hospitalization. We have reported three major findings. First, proET-1 and proADM levels were markedly increased at exacerbation and decreased significantly in the recovery and stable phases of the disease. Second, neither proET-1 nor proADM levels correlated consistently with the clinical presentation on hospital admission. Finally, and most importantly, plasma proADM levels but not plasma proET-1 levels on hospital admission independently predicted 2-year survival in patients with COPD, thus suggesting that this biomarker could be used to predict prognosis during exacerbations. A few previous s t ~ d i e shave ~ , ~examined ~ the importance of ET-1 levels in COPD patients. Sputum ET-1

Table 4 -Multivariate Cox Regression Model Analysis for the Association Between Clinical and Laboratory

Parameters on Hospital Admission and 2-Year Mortality in COPD Patients (n = 167) Cox Regression I

I

Parameters Age Charlson comorbidity score BMI Pao, Paco, Leukocyte counts C-reactive protein Procalcitonin ProET-1 ProADM FEV, % predicted Pulmonary arterial hypertension* *n = 123. t Statistically significant. www.chestjournal.org

-

8 *

R d D M OM nmolll. n 80

Hazard Ratio

95% CI

p Value

1.009 1.186

(0.949-1.073) (0.98S1.432)

0.779 0.075

0.988 0.996 1.025 0.936 1.002 1.677 0.995 2.368 1.005 1.020

(0.896-1.089) (0.971-1.021) (0.980-1.071) (0.819-1.070) (0.991-1.012) (0.961-2.924) (0.986-1.003) (1.167-4.803) (0.974-1.037) (0.35G2.975)

0.802 0.744 0.284 0.333 0.772 0.069 0.223 0.017t 0.741 0.971

P W M> OM nmolll. n =

1*n(dayr)

FIGURE3. Kaplan-Meier curves showing the probability of suMval in patients with proADM levels at hospital admission below the median (ie, < 0.84 nmoVL; n = 85) and in those with proADM levels at hospital admission above the median (ie, 2 0.84 nmoVL; n = 82; p = 0.002 [log-rank test]). CHEST I 134 I 2 I AUGUST, 2008

269

levels have been shown to increase in patients with acute exacerbations of COPD, and ET-1 has been implicated in the pathogenesis of virally mediated inflammation.21A novel finding of the current study is that ET-1 plasma levels on hospital admission are not correlated with the clinical presentation of the exacerbation or the in-hospital outcome. Additionally, and in contrast to previous assumptions, elevated circulating ET-1 levels were not associated with increased morbidity or mortality in COPD.7 This study is the first to report increased plasma proADM levels in patients with acute exacerbations of COPD. Our results are in line with previous examinations, which have described elevated adrenomedullin levels in a small subset of patients with severe stable COPD.33,49 Adrenomedullin has a range of biological actions.50 However, its mechanism of action in patients with acute exacerbations of COPD remains unclear. Adrenomedullin secretion is stimulated by tumor necrosis factor-a, interleukinI@, and lipopolysaccharide, and appears to initiate the hyperdynamic response during the early stage of bacterial i n f e ~ t i o n . ~It~ , is ~ l also involved in the regulation of the complement cascade, thereby exerting a direct bactericidal effect on selected micro0rganisms.26.5~The systemic response modulated by adrenomedullin has been observed not only in patients with sepsis but also in localized pulmonary p~ocesses.~3,53,54 Within this context, increased circulating adrenomedullin levels might contribute to the repulsion of the bacterial threat in patients experiencing exacerbations of COPD. Furthermore, adrenomedullin has been suggested to inhibit bronchoconstriction induced by histamine and acetylcholine.55 Thus, increased circulating adrenomedullin levels could potentially promote bronchodilatation in patients with exacerbations of COPD, a phenomenon that has been previously described to be involved in exacerbations of asthma.56.57 In agreement with earlier reports,33we have found a positive association between pulmonary arterial hypertension and adrenomedullin. ProADM has a protective effect against hypoxia-induced vascular remodeling and, hence, secondary pulmonary hypertension in COPD patients.58 In our study, high plasma proADM levels were consistently associated with increased mortality following acute exacerbations of COPD. Remarkably, the predictive effect of proADM levels on survival was persistent for up to 2 years, and was independent of age, comorbidity score, hypoxemia, lung function impairment, and pulmonary artery hypertension. This suggests that plasma proADM levels during an exacerbation might reflect the ability or inability of patients with COPD to cope with the acute physiologic stress related to exacerbations rather than 270

merely mirroring the severity of the underlying lung disease. In analogy to patients with coronary artery disease, who may develop ischemic changes only during cardiopulmonary exercise testing, it is tempting to speculate that those patients with reduced physiologic reserve are the ones prone to respond with increased plasma proADM levels in cases of systemic stress. Hence, proADM level could be considered a surrogate marker for overall cardiopulmonary distress and not a specific marker of airway obstruction. Previous clinical studies3l have suggested that proADM exhibits similar prognostic properties in myocardial infarction. Herein, elevated circulating adrenomedullin levels are thought to signify left ventricular dysfunction and to be negatively related to ejection f r a ~ t i o n . ~ Conversely, ~-~l in COPD patients, plasma levels of proADM are similar in patients with normal and decreased left ventricular ejection fraction. The most intuitive explanation for these findings is to assume that the stimulus leading to increased proADM levels differs between patients with COPD and those with myocardial disease. Potential etiologic candidates linked to increased proADM levels in COPD patients include the inflammation and/or infection during an exacerbation; the decreased pulmonary uptake resulting from secondary pulmonary arterial hypertension; and the counterregulatory effect on bronchoconstriction. An alternative explanation is that elevated proADM levels identify patients in whom transient myocardial dysfunction develops during systemic stress situations such as exacerbations. This is supported by the positive correlation found between left ventricular ejection fraction and plasma proADM levels and the pathophysiologic link between cardiovascular disease and COPD mortality.62However, brain natriuretic peptide, which is a more specific marker of cardiac dysfunction, failed to adequately predict survival in patients who were admitted to the hospital with exacerbations of COPD.39Further work is needed to clarifji whether proADM is only a sensitive surrogate marker of systemic cardiopulmonary stress or whether it plays an active role in regulating the inflammatory response in COPD. Specific adrenomedullin receptor antagonists and adrenomedullin antiserum may potentially provide a new therapeutic option within the pulmonary arsenal, such as endothelin in patients with primary pulmonary hypertension.63 Several limitations to our study need to be mentioned. First of all, we conducted a single-center study. However, due to the well-defined findings of our study, it seems unlikely that contradicting results would be found by investigating a larger and more diverse population. Moreover, except for echocardiography, no further assessment of cardiac function or Original Research

pulmonary arterial pressures (eg, cardiac catheterization) has been performed, and cardiac function assessment was not performed during exacerbation. This could be an explanation for the fact that, in contrast to previous studies,3ifj4 we could not demonstrate pulmonary arterial hypertension to be independently associated with increased mortality. A longer duration of follow-up could also have produced different results. Alternatively, the inclusion of a population with major comorbidities and predominantly severe or very severe COPD could have underestimated the contribution of lung function impairment and pulmonary arterial hypertension to mortality. Also we could not include all factors known to be related to a worse prognosis in patients with stable COPD in our regression analyses (eg, quality-of-life scores, rate of decline of FEV,, or dyspnea scale). However, there is as yet little knowledge about the prognostic significance of these parameters during an exacerbation. Finally, our results are preliminary and therefore hypothesis generating. Thereby, it is intriguing and has not yet been well explained how a single biomarker could explain all-cause mortality on a single measurement during an exacerbation, particularly when proADM levels did no correlate with COPD severity, pulmonary hypertension, hypoxia, or hypercarbia, all of which are known markers of disease severity, and demonstrated an association with increased mortality. In conclusion, plasma proADM levels but not plasma proET-1 levels on admission to the hospital for an acute exacerbation independently predicts survival in patients with COPD, and suggests that this biomarker could potentially be clinically useful to predict prognosis in these patients.

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