Plasma Interleukin-10 Levels and Adverse Outcomes in Acute Coronary Syndrome

CLINICAL RESEARCH STUDY Plasma Interleukin-10 Levels and Adverse Outcomes in Acute Coronary Syndrome Erdal Cavusoglu, MD, a,b Jonathan D. Marmur, MD, b Mohammad R. Hojjati, MD, PhD, b Vineet Chopra, MD, a Mitul Butala, MD, b Rakesh Subnani, BS, b Mohammad S. Huda, MD, b Sunitha Yanamadala, PhD, c Cyril Ruwende, MD, PhD, c Calvin Eng, MD, a David J. Pinsky, MD c a Division of Cardiology, Department of Medicine, Bronx Veterans Affairs Medical Center, Bronx, NY; b Division of Cardiology, Department of Medicine, SUNY Downstate Medical Center, Brooklyn, NY; c Division of Cardiovascular Medicine, Department of Medicine, University of Michigan, Ann Arbor, Mich. ABSTRACT PURPOSE OR BACKGROUND: Interleukin (IL)-10 is an immunoregulatory cytokine that is produced by a variety of cell types, such as macrophages and activated monocytes. IL-10 possesses numerous antiinflammatory, anti-thrombotic and anti-atherosclerotic properties. Furthermore, patients with acute coronary syndrome have been demonstrated to have reduced levels of IL-10 compared to their stable counterparts. For these reasons, it has been proposed that IL-10 plays a protective role in both atherogenesis and plaque vulnerability. However, 2 short-term studies on the prognostic utility of IL-10 in patients with acute coronary syndrome have provided conflicting results, with one study showing that reduced levels of IL-10 were predictors of adverse outcomes and another showing that elevated levels predicted poor outcomes. The objective of the present study was to investigate the long-term prognostic significance of baseline IL-10 levels in patients with acute coronary syndrome. METHODS: Baseline plasma IL-10 levels were measured in 193 well-characterized male patients with acute coronary syndrome who were referred for coronary angiography and followed prospectively for 5 years for the development of major adverse cardiovascular events. RESULTS: After controlling for a variety of baseline variables (including established biomarkers such as high-sensitivity C-reactive protein and N-terminal-pro-B-type natriuretic peptide), plasma IL-10 levels (whether analyzed as a continuous variable or as a categorical variable using receiver operating characteristic-derived cut point) were a strong and independent predictor of the composite outcome of death or non-fatal myocardial infarction when using a Cox proportional hazards model. CONCLUSIONS: These data demonstrate that, despite biologic plausibility for IL-10 as being a cardioprotective cytokine, elevated baseline plasma levels of IL-10 are a strong and independent predictor of long-term adverse cardiovascular outcomes in patients with acute coronary syndrome. Published by Elsevier Inc. The American Journal of Medicine (2011) 124, 724-730 KEYWORDS: Acute coronary syndrome; Biomarker; Inflammation; Interleukin-10; Prognosis Funding: None. Conflict of Interest: None of the authors have any conflicts of interest associated with the work presented in this manuscript. Authorship: All authors had access to the data and played a role in writing this manuscript. Requests for reprints should be addressed to Erdal Cavusoglu, MD, Professor of Medicine, SUNY Downstate Medical Center, 450 Clarkson Avenue, Box 1257, Brooklyn, NY 11203-2098 (E-mail address: ECavusoglu@aol.com). Interleukin (IL)-10 is an immunoregulatory cytokine produced by a variety of cell types, including activated monocytes, macrophages, and lymphocytes. 1,2 IL-10 possesses numerous anti-inflammatory properties 2,3 and has been shown to have a protective role in both atherosclerotic lesion formation and stability in animal studies. 1,4 These biological actions of IL-10 suggest a protective role for it in both atherogenesis and plaque vulnerability. Consistent with these experimental observations are clinical data demonstrating that patients with acute coronary syndrome have reduced levels of IL-10 compared with their stable counter- 0002-9343/$ -see front matter Published by Elsevier Inc. doi:10.1016/j.amjmed.2011.02.040

Cavusoglu et al IL-10 and Outcomes in ACS 725 parts, raising the possibility that low levels of IL-10 may play an etiologic role in the instability of the atherosclerotic plaque. 5 Collectively, this evidence provides biologic plausibility for IL-10 as a favorable prognostic biomarker in acute coronary syndrome. Indeed, a study in patients with acute coronary syndrome found that elevated baseline levels of IL-10 were strong and independent predictors of a reduced risk of death and myocardial infarction at 6 months of follow-up. 6 However, more recently, a large study in patients with acute coronary syndrome found that elevated baseline levels of IL-10 were independent predictors of an increased risk of the subsequent development of death and myocardial infarction at 1 year. 7 Thus, the 2 studies to date that have examined the prognostic utility of IL-10 in acute coronary syndrome have provided conflicting and contradictory findings. Furthermore, both of these studies were limited by a relatively short duration of follow-up. Accordingly, the objective of the current study was to help resolve this controversy and to do so with long-term follow-up data. To this end, we investigated the prognostic significance of baseline IL-10 levels in a group of well-characterized male patients with acute coronary syndrome who were referred for coronary angiography and followed prospectively for 5 years for the development of major adverse cardiovascular events. CLINICAL SIGNIFICANCE MATERIALS AND METHODS The study population and design have been described in detail. 8,9 The present study represents an analysis of the subpopulation of patients with acute coronary syndrome derived from a database of 389 patients. The database was generated at an urban Veterans Administration medical center and approved by the local institutional review board. Written informed consent was obtained from all patients. All patients referred to the Cardiac Catheterization Laboratory for coronary angiography at the Bronx Veterans Affairs Medical Center between January 13, 1999, and October 17, 2002, were eligible for inclusion in the database. Patients with active gastrointestinal bleeding or a hemoglobin concentration less than 8 g/dl were excluded. During the period of study enrollment, 523 unique and consecutive male patients underwent diagnostic coronary angiography. Of these 523 patients, 50 could not be enrolled because of an unexpected loss of key study personnel between January 29, 2001, and July 2, 2001. Of the remaining 473 patients, 84 were unwilling or unable to provide informed consent. IL-10 is an independent predictor of long-term adverse outcomes in acute coronary syndrome. The prognostic utility of IL-10 is independent of and comparable to that of hs-crp and NT-proBNP. The predictive value of IL-10 does not become apparent until after 1 year. IL-10 is one of few biomarkers for which 5-year prognostic data exist. There is a paradoxical association between the biological actions of IL-10 and its prognostic utility. Thus, 389 patients provided informed consent and constituted the total population from whom the database was derived. For the present study, 193 men who underwent diagnostic coronary angiography for the evaluation of acute coronary syndrome (12% with ST-segment elevation myocardial infarction, 43% with non-st-segment elevation myocardial infarction, and 45% with unstable angina pectoris) were included in the analysis. Fasting blood was obtained from all patients at the time of angiography for subsequent analysis. Commercially available kits were used to measure the plasma levels of IL-10 (Pierce Biotechnology, Rockford, Ill), high-sensitivity C-reactive protein (hs-crp; Life Diagnostics, West Chester, Pa), and N-terminal-pro-B-type natriuretic peptide (NT-proBNP; Diagnostic Automation, Calabasas, Calif). Patients were followed for the occurrence of death and myocardial infarction. Myocardial infarction during follow-up was defined by a history of chest pain with an associated elevation of troponin I or troponin T that was considered significant by local institutional criteria. A myocardial infarction was defined as fatal if its occurrence was causally and temporally related to a subsequent mortality. Otherwise, the myocardial infarction was defined as nonfatal. The information regarding the date of death was obtained using the following modalities: death certificate, social security death index, conversation with next of kin or primary physician, and review of medical records. The study population was divided into 2 groups, high or low IL-10, on the basis of the optimal receiver operating characteristic (ROC)-derived cut point for IL-10 that provided the maximal sensitivity and specificity for predicting adverse cardiovascular events. Summary statistics for the continuous variables were presented as mean standard deviation or medians with interquartile ranges, and comparisons between the 2 groups were performed with the nonparametric Wilcoxon rank-sum test. Data for the biomarkers other than IL-10 (NT-proBNP and hs-crp) were presented as medians with 25th and 75th percentiles. Log transformation was applied to all biomarkers (including IL-10) to decrease the skewness and kurtosis of the data. Categoric data were summarized as frequencies and percentages, and comparisons between groups were performed with Pearson s chi-square test or Fisher exact test if the number of observations per cell was less than 5. The predictors of the composite outcome of death or nonfatal myocardial infarction at 5 years were identified by univariate Cox regression. The following baseline variables

726 The American Journal of Medicine, Vol 124, No 8, August 2011 were studied by univariate analysis: age/10 years, family history of premature coronary artery disease, diabetes, hypertension, active tobacco use, hyperlipidemia, history of atrial fibrillation, serum creatinine, body mass index, troponin I, aspirin use, beta-blocker use, angiotensin-converting enzyme inhibitor use, angiotensin receptor blocker use, statin use, previous coronary artery bypass graft surgery, number of diseased coronary arteries, left ventricular function, congestive heart failure on presentation, myocardial infarction on presentation, hs-crp, NT-proBNP, and IL-10. IL-10 was analyzed as both a continuous and a dichotomous variable, using the ROC-derived cut point to create 2 categories. For the biomarkers (IL-10, hs-crp, and NT-proBNP), the hazard ratios represented an increase of 1 standard deviation in the respective log-transformed biomarker. Only those univariate predictors with P values.05 were subsequently entered into multivariate models. Multivariate Cox proportional hazard analyses were then performed as stepwise regressions with backward elimination to identify the independent predictors of adverse outcome at 5 years. Time to event at 5 years was presented with Kaplan Meier curves for the composite outcome of death or nonfatal myocardial infarction. Comparison between the 2 groups identified by the ROC-derived cut point for IL-10 was performed with the log-rank test. For the nonfatal myocardial infarction end point, subjects were censored after the first occurrence and no subjects contributed more than 1 end point to the analysis. All analyses used 2-sided tests, with an overall significance level of alpha 0.05. All statistical analyses were performed using SAS version 8 (SAS Institute Inc, Cary, NC). RESULTS In total, 193 men were enrolled in the study. IL-10 values were available for 182 of these patients. On the basis of ROC analysis, the optimal cut point that provided the maximal sensitivity and specificity for predicting adverse cardiovascular events was 4.9 pg/ml. By using this cut point, the study population was stratified into 2 groups (ie, 4.9 pg/ml vs 4.9 pg/ml). Baseline characteristics of the study population were stratified by the ROC-derived cut point as low and high IL-10 levels and are listed in Table 1. There was a higher incidence of C-reactive protein elevation and a higher percentage of patients who had myocardial infarction on presentation in patients with high IL-10 plasma levels compared with those with low IL-10 plasma levels. Otherwise, baseline characteristics did not significantly differ between patients in the 2 groups (Table 1). Five-year follow-up data with respect to the composite outcome of death or nonfatal myocardial infarction were available for 190 of the 193 patients (98.4% of the patients). At 5 years, there were 62 all-cause mortalities and 67 fatal or nonfatal myocardial infarctions. During this period, 93 patients, or 48.2% of the cohort, developed 1 or more component of the composite end point of death or nonfatal myocardial infarction. Thus, the total number of events for the composite outcome of death or nonfatal myocardial infarction was 93. The following baseline variables were significant for their association with clinical outcomes with P.05 on univariate analysis: age/10 years, diabetes, left ventricular function, the number of diseased coronary arteries, congestive heart failure on presentation, serum creatinine, IL-10 (both as a continuous and categoric variable), NTproBNP (as a continuous variable), and hs-crp (as a continuous variable). Together with IL-10 (analyzed both as a continuous variable and as a dichotomous variable based on the ROC-derived cut point), these significant univariate predictors of outcome were entered into multivariate models to identify the independent predictors of outcomes (Tables 2 and 3.) Congestive heart failure on presentation was not included as a covariate in multivariate models because of a very high and significant correlation between this variable and both NT-proBNP and left ventricular function (which were included in separate multivariate models). Model 1 adjusted for clinical and angiographic variables only, and model 2 also adjusted for additional biomarkers. Whether analyzed as a continuous or categoric variable, IL-10 was a strong and independent predictor of the composite outcome of death or nonfatal myocardial infarction at 5 years (Tables 2 and 3) with a hazard ratio comparable to that of NTproBNP and hs-crp. By using the ROC-derived value of 4.9 pg/ml as a prespecified cutoff point with a sensitivity of 36.6% and specificity of 81.4%, the event-free survival rate at 5 years for the group whose baseline IL-10 values were 4.9 pg/ml was 45.7% compared with 68.0% for those whose values were 4.9 pg/ml (P.0166 by log-rank test; Figure 1). DISCUSSION The most significant finding of our study was that elevated plasma levels of IL-10 at baseline were strong and independent predictors of long-term adverse cardiovascular outcomes in male patients presenting with acute coronary syndrome who were referred for coronary angiography. Specifically, we found that elevated plasma levels of IL-10 were associated with an increased risk of subsequent death or nonfatal myocardial infarction to 5 years after an index event, even after adjustment for clinically significant covariates, including other established biomarkers such as hs-crp and NT-proBNP. These data are consistent with those reported recently from the FRagmin and fast revascularisation during In- Stability in Coronary artery disease-ii (FRISC-II) investigators, 7 but are contradictory to an earlier study reporting a strong association between high levels of this antiinflammatory marker and improved outcomes in patients with acute coronary syndrome. 6 Thus, our study provides additional data on the controversial role of IL-10 as a prognostic biomarker in patients with acute coronary

Cavusoglu et al IL-10 and Outcomes in ACS 727 Table 1 Baseline Characteristics According to Interleukin-10 Status Characteristics Low IL-10 High IL-10 N 51* N 131* P Value Age (y) Mean (SD) 65.7 (9.5) 64.6 (10.3).6091 Median (IQ) 66.8 (57.0-73.5) 66.3 (55.8-73.4) Family history of premature coronary artery disease 10 (19.6%) 40 (30.5%).1381 Race.5239 Black 21 (41.2%) 47 (35.9%) Hispanic 12 (23.5%) 42 (32.1%) White 18 (35.3%) 42 (32.1%) Hyperlipidemia 33 (64.7%) 66 (50.4%).0814 24 (47.1%) 60 (45.8%).8786 Hypertension 44 (86.3%) 108 (82.4%).5315 Any tobacco use (past or present) 45 (88.2%) 105 (80.2%).1983 Active tobacco use 15 (29.4%) 53 (40.5%).1665 Congestive heart failure on presentation 9 (17.7%) 33 (25.2%).2780 MI on presentation 23 (45.1%) 82 (62.0%).0319 Atrial fibrillation 2 (3.9%) 6 (4.6%) 1.0000 BMI (kg/m 2 ) 29.4 (5.7) 28.5 (5.9).2028 29 (25.8-33.8) 27.6 (24.1-31.2) Aspirin use 45 (88.2%) 122 (93.1%).2809 Beta blocker use 39 (76.5%) 100 (76.3%).9847 ACE-I use 34 (66.7%) 76 (58.0%).2837 Statin use 30 (58.8%) 65 (49.6%).2642 LV function.8474 EF 55% 18 (38.3%) 40 (33.1%) EF 45%-54% 10 (21.3%) 30 (24.8%) EF 31%-44% 13 (27.6%) 31 (25.6%) EF 30% 6 (12.8%) 20 (16.5%) No. of diseased coronary arteries.3300 0 5 (9.8%) 19 (14.5%) 1 6 (11.8%) 23 (17.6%) 2 16 (31.4%) 29 (22.1%) 3 23 (45.1%) 51 (38.9%) 4 1 (2.0%) 9 (6.9%) Prior CABG 6 (11.8%) 12 (9.2%).5971 Serum creatinine (mg/dl) 1.1 (0.3) 1.5 (2.0).5950 1.1 (0.9-1.2) 1.1 (0.9-1.3) Troponin I (ng/ml) 6.0 (12.5) 25.8 (75.8).0987 0.4 (0.2-4.5) 1.5 (0.3-15.3) NT-proBNP (fmol/ml) 1219.1 (970.4) 1451 (1129.4).1413 869.8 (473.2-1671) 1044.4 (654.2-1940.6) hs-crp (mg/l) 15.1 (19.9) 40.2 (53.9).0027 9.8 (3.2-18.0) 15.8 (7.3-52.0) ACEI angiotensin-converting enzyme inhibitor; BMI, body mass index; CABG coronary artery bypass grafting; EF ejection fraction; hs- CRP high-sensitivity C-reactive protein; IL, interleukin; IQ interquartile; LV left ventricular; MI myocardial infarction; NT-proBNP N-terminalpro-B-type natriuretic peptide; SD, standard deviation. Data are presented as frequencies (percentages) for categoric variables and as means standard deviation or medians (interquartile ranges) for continuous variables. Low IL-10 indicates levels 4.9 pg/ml, and high IL-10 indicates levels 4.9 pg/ml. *n 182 for entire cohort because of missing IL-10 values in 11 patients. Hyperlipidemia was diagnosed in patients who had been given lipid-lowering medication or had a history of total cholesterol levels 240 mg/dl. 8 Takes into account the left main, left anterior descending, left circumflex, and right coronary arteries. syndrome. Furthermore, to our knowledge, our study provides the longest follow-up to date on the prognostic utility of IL-10 in patients with acute coronary syndrome to date. IL-10 is an immunoregulatory cytokine that is produced by various inflammatory cells, especially macrophages. 2 Numerous experimental studies have suggested an anti-inflammatory, antithrombotic, and antiatherosclerotic role for IL-10. Specif-

728 The American Journal of Medicine, Vol 124, No 8, August 2011 Table 2 Multivariate Cox Proportional Hazard Analyses for Death or Nonfatal Myocardial Infarction at 5 Years Using Interleukin-10 as a Continuous Variable Baseline Variable HR (95% CI) P Value Model 1A IL-10 1.31 (1.06-1.60).0113 Age/10 y 1.35 (1.04-1.77).0265 2.02 (1.28-3.19).0025 Serum 1.21 (1.04-1.40).0132 creatinine LV function 1.30 (1.06-1.60).0117 Model 1B IL-10 1.26 (1.03-1.54).0272 Age/10 y 1.38 (1.07-1.78).0133 2.05 (1.32-3.20).0015 NT-proBNP 1.35 (1.07-1.72).0127 hs-crp 1.32 (1.05-1.66).0178 CI confidence interval; HR hazard ratio; hs-crp high-sensitivity C-reactive protein; IL interleukin; LV left ventricular; NTproBNP N-terminal-pro-B-type natriuretic peptide. Multivariate Cox proportional hazard analyses were performed as stepwise regressions with backward elimination. Twenty-two baseline variables were initially studied by univariate analysis. Only those predictors with a P.05 were subsequently entered into multivariate models, the results of which are presented. Model 1A did not include other biomarkers (hs-crp and NT-proBNP), whereas model 1B included these markers. Because of a significant correlation between NT-proBNP and LV function (r 0.42, P.0001), LV function was not included in model 1B. ically, IL-10 has been shown to suppress macrophage function, 10 inhibit production of proinflammatory cytokines, 2,3 and suppress tissue factor expression. 11 Furthermore, animal studies have shown a protective role for IL-10 in both atherosclerotic lesion formation and stability. 1,4 Concordant with these basic observations are clinical data demonstrating decreased IL-10 levels in patients with plaque instability and acute coronary syndrome compared with patients with stable angina, suggesting that decreased IL-10 concentrations may contribute to atheromatous plaque instability in humans. 5 Indeed, in a study of 547 patients with acute coronary syndrome enrolled in the Chimeric c7e3 Anti Platelet Therapy in Unstable Refractory angina trial, Heeschen and colleagues 6 found that elevated baseline levels of serum IL-10 were associated with a more favorable prognosis (with respect to death and nonfatal myocardial infarction) at 6-month follow-up. However, in stark contrast with these findings, a more recent and larger study by the FRISC-II investigators found that elevated baseline levels of IL-10 were associated with an increased risk of death and myocardial infarction at 12 months, even though this association was weakened after adjustment for C-reactive protein and IL-6. 7 Furthermore, elevated IL-10 levels in that study were associated with a large number of common cardiovascular risk factors, leading the authors to conclude that increased IL-10 is an indicator of enhanced systemic inflammation in patients with acute coronary syndrome. Consistent with the findings reported by the FRISC-II investigators, we similarly found that elevated baseline levels of plasma IL-10 were strong predictors of the subsequent development of death and nonfatal myocardial infarction. However, in contrast with the findings by the FRISC-II investigators, we found no weakening of the association between IL-10 levels and adverse outcomes after adjusting for hs-crp. In fact, the association persisted even after adjusting for both hs-crp and NT-proBNP, 2 markers whose prognostic utility in acute coronary syndrome has been firmly established in the literature. 12,13 Furthermore, our adjusted relative risks for elevated IL-10 were higher than those observed by the FRISC-II investigators. 7 In addition, IL-10 was a predictor of outcomes whether analyzed as a continuous or categoric variable, a statistical testimony to the strength and validity of the findings. We believe that our findings extend the observations of the FRISC-II investigators to the long-term (from 1 year of follow-up to 5 years), thereby adding IL-10 to the relatively short list of biomarkers for which such long-term prognostic data exist. Although our study was relatively small in size, the long follow-up and high-risk profile of the patients led to a high event rate that allowed for statistical power. Finally, our patients were extremely well characterized with all subsequent events rigorously confirmed by multiple modalities. Table 3 Multivariate Cox Proportional Hazard Analyses for Death or Nonfatal Myocardial Infarction at 5 Years Using Interleukin-10 as a Dichotomous Variable Baseline Variable HR (95% CI) P Value Model 2A IL-10 1.94 (1.08-3.49).0268 Age/10 y 1.33 (1.02-1.72).0338 1.96 (1.24-3.10).0039 Serum 1.18 (1.02-1.37).0302 creatinine LV function 1.31 (1.07-1.62).0102 Model 2B IL-10 1.80 (1.01-3.20).0453 Age/10 y 1.36 (1.06-1.75).0155 1.99 (1.28-3.10).0024 NT-proBNP 1.28 (1.01-1.61).0390 hs-crp 1.35 (1.06-1.72).0138 CI confidence interval; HR hazard ratio; hs-crp high-sensitivity C-reactive protein; IL interleukin; LV left ventricular; NTproBNP N-terminal-pro-B-type natriuretic peptide. Multivariate Cox proportional hazard analyses were performed as stepwise regressions with backward elimination. Twenty-two baseline variables were initially studied by univariate analysis. Only those predictors with a P.05 were subsequently entered into multivariate models, the results of which are presented. Model 2A did not include other biomarkers (hs-crp and NT-proBNP), whereas model 2B included these markers. Because of a significant correlation between NT-proBNP and LV function (r 0.42, P.0001), LV function was not included in model 2B.

Cavusoglu et al IL-10 and Outcomes in ACS 729 Figure 1 Kaplan Meier curves for event-free survival according to baseline plasma IL-10 values stratified by ROC-derived cut point of 4.9 pg/ml versus 4.9 pg/ml. At 5 years, the event-free survival rate (for death or nonfatal myocardial infarction) was 68% in the low IL-10 group (ie, 4.9 pg/ml), whereas it was 45.7% in the high IL-10 group (ie, 4.9 pg/ml) (P.0166 by log-rank test). The mechanism(s) for the paradoxic and counterintuitive finding of an inverse association between IL-10 levels and adverse clinical outcomes in patients with acute coronary syndrome is unknown and beyond the scope of our study. The FRISC-II investigators have suggested that sampling time may influence IL-10 measurements (with the majority of the FRISC-II patients being sampled later than 8 hours after study randomization) and may explain the contradictory findings between their study and that of Heeschen et al. 6 Although we did not record the sampling times in our study, blood samples were drawn from our population with acute coronary syndrome at the time of their cardiac catheterization and not on initial presentation, representing an inherent delay in procurement of samples similar to that observed in the FRISC-II study. It also is conceivable that IL-10 may have other (as of yet) undefined and unknown harmful effects that could theoretically overcome any of its favorable anti-inflammatory actions in the acute coronary syndrome setting. Alternatively, and in simplistic terms, increased levels of this anti-inflammatory marker may represent a compensatory or counterregulatory mechanism during a heightened inflammatory state, as occurs in acute coronary syndrome, and may therefore represent a surrogate (rather than causal) marker of increased risk. It is noteworthy that similar seemingly contradictory and counterintuitive observations have been reported for other biomarkers, where there has been a discordance between purported in vitro biological actions and anticipated clinical prognostic utility. 8,14 For example, despite an overwhelming body of experimental evidence demonstrating that adiponectin is a cardioprotective protein with anti-inflammatory, antithrombotic, and antiproliferative actions, we and others have shown that elevated levels of this marker are associated with an increased risk of subsequent mortality and myocardial infarction in high-risk high-inflammatory states, such as acute coronary syndrome, 8,15 renal failure, 16 and peripheral vascular disease. 17 The mechanism for this paradoxical association remains unknown. 18 Thus, it is likely that the directionality of the association between the levels of a particular protein and prognosis may ultimately be a function of multiple (and unknown) factors, and not just a function of biological plausibility. Finally, it is worth noting that, on the basis of the survival curves, the predictive value of IL-10 in our study did not become apparent until after approximately 1 year. The mechanism for this curious observation is not known, but assuming the validity of this finding, it may explain the discrepant results reported by the 2 previous studies investigating the prognostic utility of IL-10 (both of which had relatively short follow-up). In addition, the fact that the study with the longer follow-up reported similar findings to ours further supports this contention, because the predictive

730 The American Journal of Medicine, Vol 124, No 8, August 2011 value of elevated IL-10 levels likely started to become apparent by 1 year in this larger study. CONCLUSIONS We found that elevated baseline plasma levels of IL-10 were independently associated with an increased risk of death and nonfatal myocardial infarction at 5-year follow-up in a cohort of men with acute coronary syndrome who were referred for coronary angiography. Furthermore, the prognostic power of IL-10 in this regard was independent of, and comparable to that of, other established biomarkers, such as hs-crp and NT-proBNP. This study is consistent with a recent large study and extends those observations to the long-term. The mechanisms for these seemingly counterintuitive findings merit further investigation. References 1. Mallat Z, Besnard S, Duriez M, et al. Protective role of interleukin-10 in atherosclerosis. Circ Res. 1999;85:e17-24. 2. de Vries JE. Immunosuppressive and anti-inflammatory properties of interleukin 10. Ann Med. 1995;27:537-541. 3. de Waal Malefyt R, Abrams J, Bennett B, Figdor CG, de Vries JE. Interleukin 10(IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes. J Exp Med. 1991;174:1209-1220. 4. Pinderski Oslund LJ, Hedrick CC, et al. Interleukin-10 blocks atherosclerotic events in vitro and in vivo. Arterioscler Thromb Vasc Biol. 1999;19:2847-2853. 5. Smith DA, Irving SD, Sheldon J, Cole D, Kaski JC. Serum levels of the antiinflammatory cytokine interleukin-10 are decreased in patients with unstable angina. Circulation. 2001;104:746-749. 6. Heeschen C, Dimmeler S, Hamm CW, et al. Serum level of the antiinflammatory cytokine interleukin-10 is an important prognostic determinant in patients with acute coronary syndromes. Circulation. 2003;107:2109-2114. 7. Malarstig A, Eriksson P, Hamsten A, Lindahl B, Wallentin L, Siegbahn A. Raised interleukin-10 is an indicator of poor outcome and enhanced systemic inflammation in patients with acute coronary syndrome. Heart. 2008;94:724-729. 8. Cavusoglu E, Ruwende C, Chopra V, et al. Adiponectin is an independent predictor of all-cause mortality, cardiac mortality, and myocardial infarction in patients presenting with chest pain. Eur Heart J. 2006;27:2300-2309. 9. Cavusoglu E, Ruwende C, Eng C, et al. Usefulness of baseline plasma myeloperoxidase levels as an independent predictor of myocardial infarction at two years in patients presenting with acute coronary syndrome. Am J Cardiol. 2007;99:1364-1368. 10. Fiorentino DF, Zlotnik A, Mosmann TR, Howard M, O Garra A. IL-10 inhibits cytokine production by activated macrophages. J Immunol. 1991;147:3815-3822. 11. Lindmark E, Tenno T, Chen J, Siegbahn A. IL-10 inhibits LPSinduced human monocyte tissue factor expression in whole blood. Br J Haematol. 1998;102:597-604. 12. Scirica BM, Morrow DA, Cannon CP, et al. Clinical application of C-reactive protein across the spectrum of acute coronary syndromes. Clin Chem. 2007;53:1800-1807. 13. Scirica BM, Cannon CP, Sabatine MS, et al. Concentrations of C-reactive protein and B-type natriuretic peptide 30 days after acute coronary syndromes independently predict hospitalization for heart failure and cardiovascular death. Clin Chem. 2009;55:265-273. 14. Cavusoglu E, Eng C, Chopra V, Clark LT, Pinsky DJ, Marmur JD. Low plasma RANTES levels are an independent predictor of cardiac mortality in patients referred for coronary angiography. Arterioscler Thromb Vasc Biol. 2007;27:929-935. 15. Schnabel R, Messow CM, Lubos E, et al. Association of adiponectin with adverse outcome in coronary artery disease patients: results from the AtheroGene study. Eur Heart J. 2008;29:649-657. 16. Menon V, Li L, Wang X, et al. Adiponectin and mortality in patients with chronic kidney disease. J Am Soc Nephrol. 2006;17:2599-2606. 17. Dieplinger B, Haltmayer M, Poelz W, Mueller T. Value of adiponectin as predictor of 5-year all-cause mortality in patients with symptomatic peripheral arterial disease: results from the Linz Peripheral Arterial Disease (LIPAD) study. Clin Chim Acta. 2009;408:87-91. 18. Teoh H, Strauss MH, Szmitko PE, Verma S. Adiponectin and myocardial infarction: a paradox or a paradigm? Eur Heart J. 2006;27: 2266-2268.