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Brief Communications |
1 Department of Laboratory Medicine, Konventhospital Barmherzige Brueder, Linz, Austria;2 Department of Internal Medicine, Krankenhaus Bad Ischl, Austria;3 Institute for Applied System Sciences and Statistics, University of Linz, Austria;4 Department of Cardiology, Medical University of Vienna, Austria;5 Paracelsus Private Medical University, Salzburg, Austria
aaddress correspondence to this author at: Department of Laboratory Medicine, Konventhospital Barmherzige Brueder, Seilerstaette 2-4, A-4020 Linz, Austria. Fax +43-732-7677-3799; e-mail thomas.mueller{at}bs-lab.at.
Abstract
Background: The soluble isoform of the interleukin-1 receptor family member ST2 (sST2) has been implicated in heart failure. The aim of the present study was to evaluate the capability of sST2 as a prognostic marker in patients with acute destabilized heart failure.
Methods: sST2 plasma concentrations were obtained in 137 patients with acute destabilized heart failure attending the emergency department of a tertiary care hospital. The endpoint was defined as all-cause mortality, and the study participants were followed up for 365 days.
Results: Of the 137 patients enrolled, 41 died and 96 survived during follow-up. At baseline the median sST2 plasma concentration was significantly higher in the patients who died than in those who survived (870 vs 342 ng/L, P <0.001). Kaplan-Meier curve analyses demonstrated that the risk ratios for mortality were 2.45 (95% CI, 0.88–6.31; P = 0.086) and 6.63 (95% CI, 2.55–10.89; P <0.001) in the second tercile (sST2, 300–700 ng/L; 11 deaths vs 34 survivors) and third tercile (sST2, >700 ng/L; 25 deaths vs 21 survivors) of sST2 plasma concentrations compared with the first tercile (sST2, 
300 ng/L; 5 deaths vs 41 survivors). In multivariable Cox proportional-hazards regression analyses, an sST2 plasma concentration in the upper tercile was a strong and independent predictor of all-cause mortality.
Conclusions: Increased sST2 concentrations determined in plasma samples drawn from patients with acute destabilized heart failure at their initial presentation indicate increased risk of future mortality. Increased sST2 plasma concentrations are independently and strongly associated with one-year all-cause mortality in these patients.
ST2 is an interleukin-1 receptor family member with transmembrane (ST2L) and soluble (sST2) isoforms(1). In the Human Gene Nomenclature Database the approved symbol for ST2 is IL1RL1 (interleukin-1 receptor-like-1). The human IL1RL1 gene was found to be located on chromosome 2(2). ST2L and sST2 are produced by alternative promoter splicing and 3' processing(3). ST2L is a membrane-bound isoform with 3 extracellular IgG domains, a single transmembrane domain, and an intracellular domain. sST2 lacks the transmembrane and intracellular domains(1). Currently, the pathophysiological role of ST2L is not fully understood, although interleukin-33 has previously been identified as a functional ligand of ST2L(4). In addition to proposed functions in several tissues, interleukin-33/ST2L signaling has recently been demonstrated to function in a crucial cardioprotective mechanism that protects the myocardium under mechanical overload(5). This finding is probably related to observations that increases of circulating sST2 predict worse prognosis in patients with chronic heart failure and those with acute myocardial infarction(6)(7). In the present work we aimed to show that increased plasma concentrations of sST2 are predictive for 1-year mortality in patients with acute destabilized heart failure.
Recently, we demonstrated that increased plasma concentrations of B-type natriuretic peptide (BNP), midregional pro-A-type natriuretic peptide (MR-proANP), midregional proadrenomedullin (MR-proADM), and the C-terminal part of the arginine vasopressin prohormone (Copeptin) were predictive for 1-year mortality in 137 consecutive patients with symptomatic acute destabilized heart failure who were treated at the emergency department of a tertiary care hospital(8). As a post hoc analysis, we used this cohort to evaluate the usefulness of sST2 as a prognostic marker in acute destabilized heart failure. Comprehensive information on the demographic and clinical characteristics of the study participants is given in the previous publication on this study cohort(8). The endpoint of our follow-up investigation was defined as all-cause mortality, and the study participants were followed up for 365 days from the time they presented to the emergency department.
During initial patient examination in our emergency department blood samples were collected for measurement of BNP concentrations and were analyzed within the next 4 hours by a commercially available assay on an AxSYM analyzer (Abbott Laboratories). Aliquots of these EDTA-plasma samples were stored at –80 °C for further analyses. One aliquot of plasma from each patient was used for determination of MR-proANP, MR-proADM, and Copeptin by commercially available immunoluminometric assays (B.R.A.H.M.S AG) as previously described(8). Another aliquot of plasma from each patient was used for determination of sST2 plasma concentrations (i.e., in these samples there was no freeze and thaw cycle before the sST2 measurements). Regarding the stability of sST2 in frozen plasma samples, a >95% mean recovery of sST2 has been reported compared to correlative fresh samples across sST2 concentrations ranging from 20 ng/L to >10 000 ng/L (James L. Januzzi, personal communication, November 12, 2007). sST2 measurement was fully-automated on a BEP® 2000 instrument (Dade Behring) with a previously described sandwich double monoclonal antibody ELISA method (Medical&Biological Laboratories)(7). All 137 plasma samples were measured in 1 batch approximately 3 years after blood collection in a blinded fashion to clinical features and biochemical data.
To evaluate the precision of the sST2 assay in our laboratory, we performed a replication study according to the Clinical and Laboratory Standards Institute (CLSI) guideline EP5-A(9). Two pooled patient plasma samples (aliquoted into twenty 1.5-mL plastic tubes and frozen at –80 °C) were used for the experiment. We analyzed these samples in duplicate in 1 run per day for 20 days on the BEP® 2000 instrument. Within-run and total imprecision (CV) were calculated with the CLSI single-run precision evaluation test(9). The sST2 assay had a within-run CV of 5.5% and a total CV of 13% at a mean concentration of 80 ng/L, and a within-run CV of 3.7% and a total CV of 7.4% at a mean concentration of 157 ng/L. The manufacturer of the sST2 assay (Medical&Biological Laboratories) claims a limit of detection of 32 ng/L.
Using test results of 100 plasma donors, we calculated reference values for sST2 by using a nonparametric percentile method (95%, double-sided). In this sample, the reference intervals for sST2 were 0–168 ng/L (in 83 of the 100 plasma donors sST2 plasma concentrations 32 ng/L were obtained).
We analyzed our data with the SPSS 13.0 software (SPSS Inc.) and the MedCalc 8.0.0.0 package (MedCalc Software). All probabilities were 2 tailed, and P values <0.05 were regarded as significant. Univariate comparisons between the patients who died and those who survived were performed with the 
2 test for categorical variables and with the nonparametric Mann–Whitney U-test for continuous variables. We used the Spearman coefficient of rank correlation (rs) to assess the relationship of sST2 concentrations with other variables. The whole study population of 137 patients with acute destabilized heart failure was then stratified according to terciles for sST2 concentrations. Using the tercile approach, we computed Kaplan-Meier estimates of the distribution of times from baseline to death, and we performed log-rank tests to compare the survival curves between the groups. Furthermore, Cox proportional-hazards regression was used to analyze the effect of several confounding risk factors on survival. In Cox proportional-hazards regression analyses the biochemical markers sST2, BNP, MR-proANP, MR-proADM, and Copeptin were dichotomized according to the plasma concentrations dividing the second and third terciles (i.e., third terciles vs first and second terciles for each marker).
Of the 137 patients with acute destabilized heart failure, 41 died and 96 survived within 365 days from the time of study enrollment. The median survival of the patients who died during follow-up was 108 days (range 3–342 days). At baseline the median sST2 plasma concentration was significantly higher in the patients who died than in those who survived (870 vs 342 ng/L, P <0.001). The complete baseline patient characteristics for the survivors and nonsurvivors have been described previously(8) (condensed data are listed in Supplemental Table 1 in the Data Supplement that accompanies the online version of this Brief Communication at http://www.clinchem.org/content/vol54/issue4).
Associations of sST2 vs BNP [rs, 0.317; 95% CI, 0.157–0.460; P <0.001], MR-proANP (rs, 0.310; 95% CI, 0.150–0.454; P <0.001), MR-proADM (rs, 0.537; 95% CI, 0.406–0.646; P <0.001), Copeptin (rs, 0.442; 95% CI, 0.296–0.567; P <0.001), estimated glomerular filtration rate (rs, –0.231; 95% CI, –0.384 to –0.066; P = 0.007), patient age (rs, –0.035; 95% CI, –0.202–0.133; P = 0.682), and body mass index (rs, –0.116; 95% CI, –0.279–0.052; P = 0.174), respectively are depicted in Supplemental Fig. 1
, A–G in the online Data Supplement.
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Fig. 1
shows the Kaplan-Meier curves of the 137 patients with acute destabilized heart failure who were stratified into 3 groups according to terciles of sST2 at baseline. Mortality was significantly higher in patients with increased baseline sST2 plasma concentrations (log-rank test for trend, P <0.001). The risk ratios for mortality were 2.45 (95% CI, 0.88–6.31; P = 0.086) and 6.63 (95% CI, 2.55–10.89; P <0.001) in the second tercile (sST2, 300–700 ng/L; 11 deaths vs 34 survivors) and third tercile (sST2, >700 ng/L; 25 deaths vs 21 survivors) of sST2 plasma concentrations compared with the first tercile (sST2, 300 ng/L; 5 deaths vs 41 survivors).
The results of Cox proportional-hazards regression analyses are given in Table 1
. As detailed, in univariate analysis an sST2 concentration >700 ng/L displayed a significant risk ratio. In multivariable Cox proportional-hazards regression analyses, an sST2 plasma concentration in the upper tercile was a strong and independent predictor of all-cause mortality.
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The main finding of the present post hoc analysis is that increased concentrations of sST2 determined in plasma samples drawn from patients with acute destabilized heart failure at their initial presentation indicate an increased risk of future mortality. Plasma concentrations of sST2 >700 ng/L predicted 1-year all-cause mortality independently of other possible confounders in our cohort. These findings are in line with results on circulating sST2 concentrations in patients with acute dyspnea very recently reported by Januzzi and colleagues(10). In a subgroup analysis of their cohort, these authors found that increased sST2 concentrations were highly predictive for 1-year mortality among patients with acute heart failure (for direct comparison of these data and ours, Kaplan-Meier curve analysis of our cohort using Januzzi et al.’s cutoff value is shown in Supplemental Fig. 2 in the online Data Supplement). Thus, taken together the findings of Januzzi et al. and our findings support the conclusion that sST2 concentration (determined at the time of patient presentation in an emergency department) seems to be an excellent marker for risk stratification in patients with acute destabilized heart failure.
We acknowledge that the present study was a post hoc evaluation of the prognostic capability of sST2 plasma concentrations. In addition, we are not able to provide data on whether sST2 decreases in response to adequate heart failure therapy or on whether a biochemical response of sST2 to therapy would modify prognosis in these patients. Therefore, further prospectively planned and adequately powered studies are necessary to clarify whether sST2 can be used for prognostic purposes in heart failure patients or whether there might be an additional value for a strategy based on a combination of sST2 and other biochemical markers (e.g., BNP or amino-terminal proBNP) and also to demonstrate that adequate therapy in heart failure patients will have any impact on circulating sST2 concentrations. Furthermore, before sST2 measurements can be introduced into clinical practice for this purpose, biological variation studies will be necessary.
Acknowledgments
Grant/Funding Support: None declared.
Financial Disclosures: T.M. has received speaking fees from Abbott Diagnostics, and B.R.A.H.M.S AG. R.P. has received speaking fees from B.R.A.H.M.S AG.
Acknowledgments: We would like to thank Critical Diagnostics, holder of the license for ST2 cardiac testing, for providing ST2 reagents free of charge, and B.R.A.H.M.S AG, holder of patent rights on the MR-proANP, MR-proADM, and Copeptin assays, for providing the assays free of charge. Critical Diagnostics and B.R.A.H.M.S AG did not play a role in the design of the study; data collection, analysis, and interpretation; or the preparation of the manuscript.
References
The following articles in journals at HighWire Press have cited this article:
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S. U. Rehman, T. Mueller, and J. L. Januzzi Jr Characteristics of the Novel Interleukin Family Biomarker ST2 in Patients With Acute Heart Failure J. Am. Coll. Cardiol., October 28, 2008; 52(18): 1458 - 1465. [Abstract] [Full Text] [PDF]
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J. Diez Serum Soluble ST2 as a Biochemical Marker of Acute Heart Failure: Future Areas of Research J. Am. Coll. Cardiol., October 28, 2008; 52(18): 1466 - 1467. [Full Text] [PDF]
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