Gut Microbiota-Dependent Trimethylamine N-Oxide Predicts Risk of Cardiovascular Events in Patients With Stroke and Is Related to Proinflammatory Monocytes

Objective- Gut microbiota-dependent metabolites, in particular trimethylamine N-oxide (TMAO), have recently been reported to promote atherosclerosis and thrombosis. Here, we examined for the first time the relation of TMAO and the risk of incident cardiovascular events in patients with recent first-ever ischemic stroke in 2 independent prospective cohorts. Moreover, the link between TMAO and proinflammatory monocytes as a potential contributing factor for cardiovascular risk in stroke patients was studied. Approach and Results- In a first study (n=78), higher TMAO plasma levels were linked with an increased risk of incident cardiovascular events including myocardial infarction, recurrent stroke, and cardiovascular death (fourth quartile versus first quartile; hazard ratio, 2.31; 95% CI, 1.25-4.23; P<0.01). In the second independent validation cohort (n=593), high TMAO levels again heralded marked increased risk of adverse cardiovascular events (fourth quartile versus first quartile; hazard ratio, 5.0; 95% CI, 1.7-14.8; P<0.01), and also after adjustments for cardiovascular risk factors including hypertension, diabetes mellitus, LDL (low-density lipoprotein) cholesterol, and estimated glomerular filtration rate (hazard ratio, 3.3; 95% CI, 1.2-10.9; P=0.04). A significant correlation was also found between TMAO levels and percentage of proinflammatory intermediate CD14⁺⁺CD16⁺ monocytes ( r=0.70; P<0.01). Moreover, in mice fed a diet enriched with choline to increase TMAO synthesis, levels of proinflammatory murine Ly6C^high monocytes were higher than in the chow-fed control group (choline: 9.2±0.5×10³ per mL versus control: 6.5±0.5×10³ per mL; P<0.01). This increase was abolished in mice with depleted gut microbiota (choline+antibiotics: 5.4±0.7×10³ per mL; P<0.001 versus choline). Conclusions- The present study demonstrates for the first time a graded relation between TMAO levels and the risk of subsequent cardiovascular events in patients with recent prior ischemic stroke. Our data support the notion that TMAO-related increase of proinflammatory monocytes may add to elevated cardiovascular risk of patients with increased TMAO levels.

Beta-1-Adrenergic Receptor Antibodies in Acute Coronary Syndrome: Is Less Sometimes More?

Background: Anti-beta-1-adrenergic receptor antibodies (anti-β₁AR Ab) are associated with ischemic cardiomyopathies (ICM). Evidence continues to emerge supporting an autoimmune component to various cardiac diseases. This study compares anti-β₁AR Ab concentrations in patients with different entities of acute coronary syndromes (ACS) to asymptomatic non-ACS patients with positron-emission computed tomography (PET/CT)-proven atherosclerosis, and healthy controls.

Methods: Serum anti-β₁AR Ab IgG concentrations were measured in 212 ACS patients, 100 atherosclerosis patients, and 62 controls using ELISA. All ACS patients underwent coronary angiography. All 374 patients participating completed a structured questionnaire regarding traditional cardiovascular risk factors. ACS patients were followed up for 6 months.

Results: Patients with ACS exhibited lower anti-β₁AR Ab levels compared to patients with atherosclerosis or healthy controls (both p < 0.001). No differences in the ab levels were evident between healthy controls and patients with atherosclerosis. In the ACS groups, lower concentrations were found in patients with ST-elevation myocardial infarction (STEMI) (0.67 μg/ml) compared to patients with angina pectoris (AP) and non-ST elevation myocardial infarction (NSTEMI) (both 0.76 μg/ml, p = 0.008). Anti-β₁AR Ab levels ≤ 0.772 μg/ml were predictive for death and reinfarction (AUC 0.77, p = 0.006). No significant correlations between anti-β₁AR Ab levels and atherosclerotic burden or traditional cardiovascular risk factors were identified.

Conclusions: Lower anti-β₁AR Ab concentrations appear to characterize ACS phenotypes and could serve as diagnostic and prognostic markers independent from traditional risk factors for atheroscle. The prognostic predictive value of anti-β₁AR Ab in ACS remains to be confirmed in larger studies.

Reg3β is associated with cardiac inflammation and provides prognostic information in patients with acute coronary syndrome

BACKGROUND

Regenerating islet-derived protein 3 beta (Reg3β) is a cardiomyocyte-derived chemokine for macrophages that is upregulated after myocardial infarction (MI) in mice. Here, we hypothesized that monitoring Reg3β expression might provide specific information on the degree of cardiac inflammation, which is a key determinant in disease progression and prognosis of patients with acute coronary syndrome (ACS).

METHODS AND RESULTS

The expression of Reg3β and other inflammatory markers including C-reactive protein (CRP) and myeloperoxidase (MPO) was measured by immunoblotting at serial time points in the hearts and serum of mice with acute MI. We identified a rapid increase of Reg3β, CRP and MPO expression in cardiac tissue and serum within the first 24 h after MI. The expression of Reg3β peaked at day 4 and thereby paralleled the kinetic profile of the early immune-inflammatory response at sites of cardiac injury, which has been characterized by multicolor flow cytometry. In a retrospective analysis including 322 ACS patients and 117 apparently healthy individuals, we detected increased Reg3β serum concentrations in ACS patients on admission by ELISA. Multiple regression analysis revealed significant relationships between Reg3β and hs-CRP, age, diabetes and NT-proBNP in ACS. Moreover, elevated Reg3β levels on admission were associated with an increased risk of death independent of cardiovascular risk factors and hs-CRP.

CONCLUSIONS

Reg3β is a prognostic biomarker for ACS and is strongly associated with the intensity of cardiac inflammation. Accordingly, Reg3β may complement established strategies of acute risk assessment in the management of ACS.

Antibodies against MYC-Associated Zinc Finger Protein: An Independent Marker in Acute Coronary Syndrome?

Introduction

Atherosclerosis is considered the pathophysiology underlying cardiovascular (CVD), cerebrovascular, and peripheral vascular diseases. Evidence supporting an autoimmune component is emerging, with imaging studies correlating MYC-associated zinc finger protein antibody (MAZ-Ab) optical density (OD) with plaque activity. This study compares MAZ-Ab OD on ELISA testing among patients presenting with acute coronary syndromes (ACSs) to healthy controls and investigates the association of MAZ-Ab to traditional CVD risk factors.

Methods

Patients admitted with ACSs between August 2007 and July 2011 were included. Serum samples taken at presentation were retrospectively tested for MAZ-Ab and compared with serum from healthy volunteers with no CVD risk factors. Large-scale assessment of post-ACS prognostic relevance was performed using the established PLATO cohort.

Results

In total 174 ACS patients and 96 controls were included. Among ACS patients, median MAZ-Ab OD was higher compared with controls (0.46 vs. 0.27; p = 0.001). Although the majority of ACS patients (116/174; 67%) had suffered from a ST-elevation myocardial infarction, no significant differences in MAZ-Ab titers were evident between ACS subtypes (p = 0.682). No associations between MAZ-Ab OD and conventional CVD risk factors were identified. Large-scale testing revealed no prognostic stratification regarding reinfarction (OR 1.04 [95% CI: 0.94–1.16]; p = 0.436).

Conclusion

MAZ-Ab OD was higher or all ACS phenotypes compared with controls. Given current understanding of MAZ-Ab function, these findings support an autoimmune component to CVD independent of conventional risk factors and indeed the extent of end-organ damage.

Risk scores and biomarkers for the prediction of 1-year outcome after transcatheter aortic valve replacement

BACKGROUND

Up to 50% of the patients still die or have to be rehospitalized during the first year after transcatheter aortic valve replacement (TAVR). This emphasizes the need for more strategic patient selection. The aim of this prospective observational cohort study was to compare the prognostic value of risk scores and circulating biomarkers to predict all-cause mortality and rehospitalization in patients undergoing TAVR.

METHODS

We calculated the hazard ratios and C-statistics (area under the curve [AUC]) of 4 risk scores (logistic European System for Cardiac Operative Risk Evaluation [EuroSCORE], EuroSCORE II, Society of Thoracic Surgeons predicted risk of mortality, and German aortic valve score) and 5 biomarkers of inflammation and/or myocardial dysfunction (high-sensitivity C-reactive protein, growth differentiation factor (GDF)-15, interleukin-6, interleukin-8, and N-terminal pro-B-type natriuretic peptide) for the risk of death (n = 80) and the combination of death or rehospitalization (n = 132) during the first year after TAVR in 310 consecutive TAVR patients.

RESULTS

The EuroSCORE II and GDF-15 had the strongest predictive value for 1-year mortality (EuroSCORE II, AUC 0.711; GDF-15, AUC 0.686) and for the composite end point (EuroSCORE II, AUC 0.690; GDF-15, AUC 0.682). When added to the logistic EuroSCORE and EuroSCORE II, GDF-15 enhanced the prognostic performance of the score and enabled substantial reclassification of patients. Combinations of increasing tertiles of the logistic EuroSCORE or EuroSCORE II and GDF-15 allowed the stratification of the patients into subgroups with mortality rates ranging from 4.0% to 49.1% and death/rehospitalization rates ranging from 15.3% to 68.4%.

CONCLUSIONS

Our study identified GDF-15 in addition to the logistic EuroSCORE and the EuroSCORE II as the most promising predictors of a poor outcome after TAVR.

Diabetes-associated microRNAs in pediatric patients with type 1 diabetes mellitus: a cross-sectional cohort study

CONTEXT

Circulating microRNAs (miRNAs/miRs) are used as novel biomarkers for diseases. miR-21, miR-126, and miR-210 are known to be deregulated in vivo or in vitro under diabetic conditions.

OBJECTIVE

The aim of this study was to investigate the circulating miR-21, miR-126, and miR-210 in plasma and urine from pediatric patients with type 1 diabetes and to link our findings to cardiovascular and diabetic nephropathy risk factors in children with type 1 diabetes.

DESIGN

miR-21, miR-126, and miR-210 concentrations were measured with quantitative RT-PCR in plasma and urine samples from 68 pediatric patients with type 1 diabetes and 79 sex- and age-matched controls.

SETTING

The study consisted of clinical pediatric patients with type 1 diabetes.

PATIENTS OR OTHER PARTICIPANTS

Inclusion criterion for patients was diagnosed type 1 diabetes. Exclusion criteria were febrile illness during the last 3 months; chronic inflammatory or rheumatic disease; hepatitis; HIV; glucocorticoid treatment; liver, renal, or cardiac failure; or hereditary dyslipidemia. Patients were age and sex matched to controls.

MAIN OUTCOME MEASURE(S)

Main outcome parameters were changes in miR-21, miR-126, and miR-210 concentration in plasma and urine from type 1 diabetic patients compared with corresponding controls.

RESULTS

Circulating miRNA levels of miR-21 and miR-210 were significantly up-regulated in the plasma and urine of the type 1 diabetic patients. Urinary miR-126 levels in diabetic patients were significantly lower than in age- and gender-matched controls and negatively correlated between the patient's glycated hemoglobin mean and miR-126 concentration value. In contrast, circulating miR-126 levels in plasma were comparable in both cohorts. For urinary miR-21, we found by an adjusted receiver-operating characteristic-curve analysis with an area under the curve of 0.78.

CONCLUSIONS

Type 1 diabetic pediatric patients revealed a significant deregulation of miR-21, miR-126, and miR-210 in plasma and urinary samples, which might indicate an early onset of diabetic-associated diseases.

Abstract 133: Prognostic Utility of the GDF-15/FSTL-1 Axis for Adverse Cardiac and Limb Events in Patients With Peripheral Artery Disease

Background: Peripheral artery disease (PAD) confers greater vulnerability to cardiovascular events. Inflammatory activation and tissue ischemia induce expression of a vasoprotective cytokine network including GDF15 and FSTL1. We sought to evaluate the clinical utility of novel vascular stress biomarkers for risk stratification in PAD.

Methods and Results: We followed 245 PAD patients prospectively over two years for adverse cardiac events (n=40, myocardial infarction, unstable angina, coronary revascularization, transient ischemic event, stroke, congestive heart failure, cardiac death) and adverse limb events (n=52, worsening claudication, peripheral revascularization, critical limb ischemia, amputation, graft or stent failure). At baseline, we measured serum GDF15 and FSTL-1 and disease severity by the ankle-brachial index (ABI). In survival analyses, higher GDF15 was associated with both adverse cardiac and limb events (P<0.0001, P<0.01). FSTL-1 was associated with adverse limb (P=0.03) but not cardiac events. In multivariable models adjusting for relevant covariates including ABI, higher GDF15 remained associated with higher risk of limb events (HR 1.83, 95% CI 1.10, 3.06, P=0.02) and cardiac events (HR 1.92, 95% CI 1.09, 3.32, P=0.02). There was a trend for an association of higher FSTL1 with limb events (HR 2.34, 95% CI 0.93, 5.75, P=0.07). Addition of GDF15 to clinical variables led to an increase in the c statistic (P<0.05) and net reclassification improvement (P<0.01) for both cardiac and limb events.

Conclusions: Our findings show that vascular stress markers involving the GDF15-FSTL1 axis provide additional prognostic value over clinical factors and disease severity for predicting adverse cardiac and limb events in patients with PAD.

Diagnostic performance of rising, falling, or rising and falling kinetic changes of high-sensitivity cardiac troponin T in an unselected emergency department population

BACKGROUND

Current ESC guidelines for the diagnosis of myocardial infarction consider a rise and/or fall of cardiac biomarkers. However, whether rising or falling patterns of high-sensitivity cardiac troponin T (hs-cTnT) improve the discrimination of ST-elevation myocardial infarction (non-STEMI) from non-acute coronary syndromes (ACS) has not been evaluated yet.

METHODS

We compared protocols of rising and falling absolute and relative hs-cTnT changes in an unselected emergency department population.

RESULTS

A total of 635 patients with unstable angina pectoris (UAP), non-STEMI, or acute symptoms and increased hs-cTnT (>99th percentile) were enrolled. Of these, 572 patients met the inclusion criteria of consistently rising patterns (n=254, 44.4%), consistently falling patterns (n=224, 39.2%), or falling patterns after an initial rise (n=94, 16.4%). Final diagnoses included 66 (11.5%) patients with UAP, 141 (24.7%) patients with non-STEMI, and 365 (63.8%) patients with hs-cTnT elevations not due to ACS. Rising values were found more frequently in patients with non-STEMI, as compared to non-ACS (OR 3.69, 95% CI 2.46-5.53; p<0.0001), and falling patterns were observed more frequently in patients with non-ACS conditions (OR 3.56, 95% CI 2.24-5.63; p<0.001). Addition of rising but not falling changes increased diagnostic performance of hs-cTnT concentrations at presentation: positive: AUC 0.680 (95% CI 0.618-0.742) vs. 0.861 (95% CI 0.822-0.900; p<0.0001), negative: AUC 0.678 (95% CI 0.545-0.812) vs. 0.741 (95% CI 0.635-0.847). A 20% criterion as proposed by ESC guidelines performed equally for positive and negative changes only when admission hs-cTnT values were considered: AUC 0.785 (95% CI 0.726-0.845) vs. AUC 0.763 (95% CI 0.681-0.845); p=ns.

CONCLUSIONS

Detection of rising but not falling hs-cTnT values improves discrimination of non-STEMI from non-ACS in an unselected emergency department population.

Highly specific detection of myostatin prodomain by an immunoradiometric sandwich assay in serum of healthy individuals and patients

Background

Myostatin is a muscle derived factor that functions as a negative regulator of skeletal muscle growth. Induction of myostatin expression was observed in rodent models of muscle wasting and in cachectic patients with cancer or pulmonary disease. Therefore, there is an increasing interest to use serum myostatin as a biomarker.

Methods

We established an immunoradiometric sandwich assay (IRMA), which uses a commercially available chicken polyclonal, affinity purified antibody directed against human myostatin prodomain. We determined the serum concentrations of myostatin prodomain in 249 healthy individuals as well as 169 patients with heart failure, 53 patients with cancer and 44 patients with chronic pulmonary disease.

Results

The IRMA had a detection limit of 0.7ng/ml, an intraassay imprecision of ≤14.1% and an interassay imprecision of ≤ 18.9%. The specificity of our assay was demonstrated by size exclusion chromatography, detection of myostatin by Western-blotting and a SMAD-dependent transcriptional-reporter assay in the signal-rich serum fractions, as well as lack of interference by unspecific substances like albumin, hemoglobin or lipids. Myostatin prodomain was stable at room temperature and resistant to freeze-thaw cycles. Apparently healthy individuals over the age of 55 had a median myostatin prodomain serum concentration of 3.9ng/ml (25^th-75^th percentiles, 2-7ng/ml) and we could not detect increased levels in patients with stable chronic heart failure or cancer related weight loss. In contrast, we found strongly elevated concentrations of myostatin prodomain (median 26.9ng/ml, 25^th-75^th percentiles, 7-100ng/ml) in the serum of underweight patients with chronic pulmonary disease.

Conclusions

We established a highly specific IRMA for the quantification of myostatin prodomain concentration in human serum. Our assay could be useful to study myostatin as a biomarker for example in patients with chronic pulmonary disease, as we detected highly elevated myostatin prodomain serum levels in underweight individuals of this group.

Incremental Prognostic Value of Biomarkers beyond the GRACE (Global Registry of Acute Coronary Events) Score and High-Sensitivity Cardiac Troponin T in Non-ST-Elevation Acute Coronary Syndrome

BACKGROUND

Guidelines recommend the use of validated risk scores and a high-sensitivity cardiac troponin assay for risk assessment in non-ST-elevation acute coronary syndrome (NSTE-ACS). The incremental prognostic value of biomarkers in this context is unknown.

METHODS

We calculated the Global Registry of Acute Coronary Events (GRACE) score and measured the circulating concentrations of high-sensitivity cardiac troponin T (hs-cTnT) and 8 selected cardiac biomarkers on admission in 1146 patients with NSTE-ACS. We used an hs-cTnT threshold at the 99th percentile of a reference population to define increased cardiac marker in the score. The magnitude of the increase in model performance when individual biomarkers were added to GRACE was assessed by the change (Δ) in the area under the receiver-operating characteristic curve (AUC), integrated discrimination improvement (IDI), and category-free net reclassification improvement [NRI(&gt;0)].

RESULTS

Seventy-eight patients reached the combined end point of 6-month all-cause mortality or nonfatal myocardial infarction. The GRACE score alone had an AUC of 0.749. All biomarkers were associated with the risk of the combined end point and offered statistically significant improvement in model performance when added to GRACE (likelihood ratio test P ≤ 0.015). Growth differentiation factor 15 [ΔAUC 0.039, IDI 0.049, NRI(&gt;0) 0.554] and N-terminal pro–B-type natriuretic peptide [ΔAUC 0.024, IDI 0.027, NRI(&gt;0) 0.438] emerged as the 2 most promising biomarkers. Improvements in model performance upon addition of a second biomarker were small in magnitude.

CONCLUSIONS

Biomarkers can add prognostic information to the GRACE score even in the current era of high-sensitivity cardiac troponin assays. The incremental information offered by individual biomarkers varies considerably, however.

A signature of circulating microRNAs differentiates takotsubo cardiomyopathy from acute myocardial infarction

Aims

Takotsubo cardiomyopathy (TTC) remains a potentially life-threatening disease, which is clinically indistinguishable from acute myocardial infarction (MI). Today, no established biomarkers are available for the early diagnosis of TTC and differentiation from MI. MicroRNAs (miRNAs/miRs) emerge as promising sensitive and specific biomarkers for cardiovascular disease. Thus, we sought to identify circulating miRNAs suitable for diagnosis of acute TTC and for distinguishing TTC from acute MI.

Methods and results

After miRNA profiling, eight miRNAs were selected for verification by real-time quantitative reverse transcription polymerase chain reaction in patients with TTC (n = 36), ST-segment elevation acute myocardial infarction (STEMI, n = 27), and healthy controls (n = 28). We quantitatively confirmed up-regulation of miR-16 and miR-26a in patients with TTC compared with healthy subjects (both, P < 0.001), and up-regulation of miR-16, miR-26a, and let-7f compared with STEMI patients (P < 0.0001, P < 0.05, and P < 0.05, respectively). Consistent with previous publications, cardiac specific miR-1 and miR-133a were up-regulated in STEMI patients compared with healthy controls (both, P < 0.0001). Moreover, miR-133a was substantially increased in patients with STEMI compared with TTC (P < 0.05). A unique signature comprising miR-1, miR-16, miR-26a, and miR-133a differentiated TTC from healthy subjects [area under the curve (AUC) 0.835, 95% CI 0.733–0.937, P < 0.0001] and from STEMI patients (AUC 0.881, 95% CI 0.793–0.968, P < 0.0001). This signature yielded a sensitivity of 74.19% and a specificity of 78.57% for TTC vs. healthy subjects, and a sensitivity of 96.77% and a specificity of 70.37% for TTC vs. STEMI patients. Additionally, we noticed a decrease of the endothelin-1 (ET-1)-regulating miRNA-125a-5p in parallel with a robust increase of ET-1 plasma levels in TTC compared with healthy subjects (P < 0.05).

Conclusion

The present study for the first time describes a signature of four circulating miRNAs as a robust biomarker to distinguish TTC from STEMI patients. The significant up-regulation of these stress- and depression-related miRNAs suggests a close connection of TTC with neuropsychiatric disorders. Moreover, decreased levels of miRNA125a-5p as well as increased plasma levels of its target ET-1 are in line with the microvascular spasm hypothesis of the TTC pathomechanism.

Identification of follistatin-like 1 by expression cloning as an activator of the growth differentiation factor 15 gene and a prognostic biomarker in acute coronary syndrome

BACKGROUND

Growth differentiation factor 15 (GDF15) is a stress-responsive cytokine and biomarker that is produced after myocardial infarction and that is related to prognosis in acute coronary syndrome (ACS). We hypothesized that secreted proteins that activate GDF15 production may represent new ACS biomarkers.

METHODS

We expressed clones from an infarcted mouse heart cDNA library in COS1 cells and assayed for activation of a luciferase reporter gene controlled by a 642-bp fragment of the mouse growth differentiation factor 15 (GDF15) gene promoter. We measured the circulating concentrations of follistatin-like 1 (FSTL1) and GDF15 in 1369 patients with ACS.

RESULTS

One cDNA clone that activated the GDF15 promoter-luciferase reporter encoded the secreted protein FSTL1. Treatment with FSTL1 activated GDF15 production in cultured cardiomyocytes. Transgenic production of FSTL1 stimulated GDF15 production in the murine heart, whereas cardiomyocyte-selective deletion of FSTL1 decreased production of GDF15 in cardiomyocytes, indicating that FSTL1 is sufficient and required for GDF15 production. In ACS, FSTL1 emerged as the strongest independent correlate of GDF15 (partial R(2) = 0.26). A total of 106 patients died of a cardiovascular cause during a median follow-up of 252 days. Patients with an FSTL1 concentration in the top quartile had a 3.7-fold higher risk of cardiovascular death compared with patients in the first 3 quartiles (P < 0.001). FSTL1 remained associated with cardiovascular death after adjustment for clinical, angiographic, and biochemical variables.

CONCLUSIONS

Our study is the first to use expression cloning for biomarker discovery upstream of a gene of interest and to identify FSTL1 as an independent prognostic biomarker in ACS.

Adjustment of the GRACE score by growth differentiation factor 15 enables a more accurate appreciation of risk in non-ST-elevation acute coronary syndrome

AIMS

The aim of the study was to evaluate whether knowledge of the circulating concentration of growth differentiation factor 15 (GDF-15) adds predictive information to the Global Registry of Acute Coronary Events (GRACE) score, a validated scoring system for risk assessment in non-ST-elevation acute coronary syndrome (NSTE-ACS). We also evaluated whether GDF-15 adds predictive information to a model containing the GRACE score and N-terminal pro-B-type natriuretic peptide (NT-proBNP), a prognostic biomarker already in clinical use.

METHODS AND RESULTS

The GRACE score, GDF-15, and NT-proBNP levels were determined on admission in 1122 contemporary patients with NSTE-ACS. Six-month all-cause mortality or non-fatal myocardial infarction (MI) was the primary endpoint of the study. To obtain GDF-15- and NT-proBNP-adjusted 6-month estimated probabilities of death or non-fatal MI, statistical algorithms were developed in a derivation cohort (n = 754; n = 66 reached the primary endpoint) and applied to a validation cohort (n = 368; n = 33). Adjustment of the GRACE risk estimate by GDF-15 increased the area under the receiver-operating characteristic curve (AUC) from 0.79 to 0.85 (P < 0.001) in the validation cohort. Discrimination improvement was confirmed by an integrated discrimination improvement (IDI) of 0.055 (P = 0.005). A net 31% of the patients without events were reclassified into lower risk, and a net 27% of the patients with events were reclassified into higher risk, resulting in a total continuous net reclassification improvement [NRI(>0)] of 0.58 (P = 0.002). Addition of NT-proBNP to the GRACE score led to a similar improvement in discrimination and reclassification. Addition of GDF-15 to a model containing GRACE and NT-proBNP led to a further improvement in model performance [increase in AUC from 0.84 for GRACE plus NT-proBNP to 0.86 for GRACE plus NT-proBNP plus GDF-15, P = 0.010; IDI = 0.024, P = 0.063; NRI(>0) = 0.42, P = 0.022].

CONCLUSION

We show that a single measurement of GDF-15 on admission markedly enhances the predictive value of the GRACE score and provides moderate incremental information to a model including the GRACE score and NT-proBNP. Our study is the first to provide simple algorithms that can be used by the practicing clinician to more precisely estimate risk in individual patients based on the GRACE score and a single biomarker measurement on admission. The rigorous statistical approach taken in the present study may serve as a blueprint for future studies exploring the added value of biomarkers beyond clinical risk scores.

Circulating Concentrations of Follistatin-Like 1 in Healthy Individuals and Patients with Acute Coronary Syndrome as Assessed by an Immunoluminometric Sandwich Assay

Background: Follistatin-like 1 (FSTL1) is a 308–amino acid secreted glycoprotein. Tissue levels of FSTL1 are induced in animal models and patients with chronic inflammatory and cardiovascular disease. We hypothesized that FSTL1 can be measured in the human circulation and used as a biomarker in acute coronary syndrome (ACS).

Methods: We developed an immunoluminometric assay (ILMA), assessed the preanalytic characteristics of FSTL1, and determined circulating FSTL1 concentrations in 120 apparently healthy individuals and 216 patients with ACS.

Results: The assay had a limit of detection of 0.17 μg/L, limit of quantification of 1.02 μg/L, intraassay imprecision of ≤12.7%, and interassay imprecision of ≤15.4%. Selectivity was demonstrated with size-exclusion chromatography and lack of cross-reactivity with related proteins. The assay was not appreciably influenced by unrelated biological substances. FSTL1 in serum or whole blood was stable at room temperature for 48 h and was resistant to 4 freeze-thaw cycles. Measured FSTL1 concentrations in citrated plasma and heparin-treated plasma were 18% and 17% lower, respectively, than concentrations measured in serum. Apparently healthy individuals presented with a median FSTL1 serum concentration of 7.18 (range 1.06–18.49) μg/L. Serum FSTL1 concentrations were increased in ACS and related to the risk of all-cause mortality during follow-up.

Conclusions: The ILMA permits detection of FSTL1 in human serum and plasma. We expect that the favorable preanalytic characteristics of FSTL1 and the reference limits defined here for apparently healthy individuals will facilitate future studies of FSTL1 as a biomarker in various disease settings, including ACS.