suPAR in cardiovascular disease.

Soluble urokinase plasminogen activator receptor (suPAR), the soluble counterpart of urokinase plasminogen activator receptor, is found in the circulation at various levels. suPAR and its parent molecule, cell surface uPAR, exhibit similar structure and extracellular functional roles facilitating fibrinolysis, cellular adhesion, and migration. Studies have assessed the correlation between suPAR in cardiovascular disease (CVD). It is postulated that suPAR may serve as an indicator of inflammatory activation and burden during CVD progression. Increased suPAR independently predicts poorer outcomes in acute coronary syndromes, in heart failure, as well as in coronary artery disease and atherosclerosis. To guide translation into clinical utization, suPAR has been assessed in numerous CVD settings for improved risk discrimination independently or in association with established traditional risk factors. Whilst the involvement of suPAR has been explored in other diseases such as kidney diseases and cancer, there is only emerging evidence of suPAR's mechanistic involvement in cardiovascular disease. In this review, we provide a background into suPAR and its potential role as a biomarker in CVD.

Prognostic performance of soluble urokinase plasminogen activator receptor for heart failure or mortality in Western and Asian patients with acute breathlessness.

AIMS: The performance of circulating soluble urokinase plasminogen activator receptor (suPAR) for predicting the composite endpoint of subsequent heart failure (HF) hospitalisation and/or death at 1 year was assessed in (i) patients with undifferentiated breathlessness, and generalisability was compared in (ii) disparate Western versus Asian sub-cohorts, and in (iii) the sub-cohort adjudicated with HF. METHODS AND RESULTS: Patients with acute breathlessness were recruited from the emergency departments in New Zealand (NZ, n = 612) and Singapore (n = 483). suPAR measured in the presentation samples was higher in patients incurring the endpoint (n = 281) compared with survivors (5.2 ng/mL vs 3.1 ng/mL, P < 0.0001). The discriminative power of suPAR for endpoint prediction was c-statistic of 0.77 in the combined population, but was superior in Singapore than NZ (c-statistic: 0.83 vs 0.71, P < 0.0001). Although the highest suPAR tertile (>4.37 ng/mL) was associated with risks of >4-fold in NZ, >20-fold in Singapore, and ≥3-fold in HF for incurring the outcome, there was no interaction between country and suPAR levels after adjustment. Multivariable analysis indicated suPAR to be robust in predicting HF/death at 1-year [hazard ratio: 1.9 (95% CI:1.7 to 2.0) per SD increase] and improved risk discrimination for outcome prediction in HF (∆0.06) and for those with NT-proBNP >1000 pg/mL (∆0.02). CONCLUSION: suPAR is a strong independent predictor of HF and/or death at 1 year in acutely breathless patients, in both Asian and Western cohorts, and in HF. suPAR may improve stratification of acutely breathless patients, and in acute HF, for risk of later onset of heart failure or mortality.

Convalescent Growth Differentiation Factor-15 and Long-Term Outcomes after an Acute Coronary Syndrome.

BACKGROUND: Growth differentiation factor-15 (GDF-15) has been shown to be associated with adverse clinical outcomes in patients after an acute coronary syndrome when measured soon after an event. Although dynamic in the acute phase after myocardial injury, GDF-15 has been shown to remain stable during convalescence. In this study, we aimed to assess the value of GDF-15 as a long-term prognostic marker for clinical outcomes when measured in the convalescent phase following an acute coronary syndrome. METHODS: GDF-15 concentrations were measured in 1945 patients who were recruited between 2002 and 2009 to the Coronary Disease Cohort Study. For this analysis, follow-up was curtailed at 10 years and association of GDF-15 with all-cause death, cardiovascular death, recurrent myocardial infarction, and heart failure hospitalizations were assessed with multivariate Cox proportional hazard regression analysis. RESULTS: After 10 years of follow-up, there were 648 deaths (348 from cardiovascular causes), 500 admissions for myocardial infarction, and 436 for heart failure. Four-month convalescent GDF-15 demonstrated a robust independent association with all endpoints, which remained after adjustment for Global Registry of Acute Coronary Events score and other convalescent biomarkers. When compared to the lowest quartile of GDF-15 concentrations, those in the highest quartile had a 3-fold increased risk of all-cause death. CONCLUSIONS: Convalescent plasma GDF-15 is a strong and independent predictor of 10-year all-cause death, cardiovascular death, recurrent myocardial infarction, and heart failure admission following an acute coronary syndrome. AUSTRALIAN NEW ZEALAND CLINICAL TRIALS REGISTRY TRIAL ID: ACTRN12605000431628.

Circulating erythroferrone has diagnostic utility for acute decompensated heart failure in patients presenting with acute or worsening dyspnea.

Objectives: In dyspneic patients with atrial fibrillation (AF) or obesity, the diagnostic performance of NT-proBNP for acute heart failure is reduced. We evaluated the erythroblast derived protein erythroferrone (ERFE) as an ancillary biomarker for the diagnosis of acute decompensated heart failure (ADHF) in these comorbid subgroups in both Western and Asian populations. Methods: The diagnostic performance of ERFE (Intrinsic Lifesciences) and NT-proBNP (Roche Cobas e411) for ADHF was assessed in 479 New Zealand (NZ) and 475 Singapore (SG) patients presenting with breathlessness. Results: Plasma ERFE was higher in ADHF, compared with breathlessness from other causes, in both countries (NZ; 4.9 vs. 1.4 ng/ml, p < 0.001) and (SG; 4.2 vs. 0.4 ng/ml, p = 0.021). The receiver operating characteristic (ROC) areas under the curve (AUCs) for discrimination of ADHF were reduced in the NZ cohort compared to SG for ERFE (0.75 and 0.84, p = 0.007) and NT-proBNP (0.86 and 0.92, p = 0.004). Optimal cut-off points for ERFE yielded comparable sensitivity and positive predictive values in both cohorts, but slightly better specificity, negative predictive values and accuracy in SG compared with NZ. In patients with AF, the AUC decreased for ERFE in each cohort (NZ: 0.71, n = 105, SG: 0.61, n = 44) but increased in patients with obesity (NZ: 0.79, n = 150, SG: 0.87, n = 164). Conclusions: Circulating ERFE is higher in patients with ADHF than in other causes of new onset breathlessness with fair diagnostic utility, performing better in Asian than in Western patients. The diagnostic performance of ERFE is impaired in patients with AF but not patients with obesity.

Analytical and biological assessment of circulating human erythroferrone.

BACKGROUND: Erythroferrone (ERFE) is an erythroid hormone putatively involved in stress erythropoiesis. Its regional clearance and circulating form in humans, as well as levels in normal health and coronary disease remain unclear. METHODS: To establish a reference interval, ERFE was measured in 155 healthy volunteers using the Intrinsic LifeSciences ELISA. To identify trans-organ gradients in ERFE, regional blood sampling was undertaken in patients (n = 13) undergoing clinically indicated cardiac catheterisation. The Intrinsic ELISA was assessed for reproducibility, stability, linearity and possible cross-reactivity, interference and anticoagulant effects. Circulating forms of ERFE were evaluated by HPLC. RESULTS: In healthy individuals, the median concentration of ERFE was 0.51 ng/mL (IQR: 0.12-1.25), with men (n = 78) having higher levels than women (n = 77) (0.67 vs 0.32 ng/mL, p = 0.0001). ERFE concentrations in trans-organ sampling revealed no clear organ of clearance or production. Samples with high endogenous ERFE levels were suppressed by haemoglobin (≥2 g/L), bilirubin (≥200 µmol/L), lipaemia (>1 g/L), and freeze thawing (≥2 cycles), but this was not observed with low ERFE concentrations. Endogenous ERFE immunoreactivity was 46% higher in EDTA plasma compared with serum and lithium heparin plasma. On SE-HPLC, ERFE eluted as intact and cleaved forms. CONCLUSION: We provide a useful reference range for ERFE in EDTA plasma. We found no specific site of secretion or clearance. The Intrinsic ELISA performed adequately but is limited by interference and stability when endogenous levels are high. Circulating forms are multiple and complex.

Analytical, biochemical and clearance considerations of soluble urokinase plasminogen activator receptor (suPAR) in healthy individuals.

BACKGROUND: Soluble urokinase plasminogen activator receptor (suPAR) is an emerging marker of cardiovascular disease burden. Appropriate assessment of assay performance and reference interval are required to enable interpretation of results to facilitate its clinical application. METHODS: suPAR was measured using the suPARnostic® ELISA in 155 healthy volunteers. Assay performance was assessed for anticoagulant effect, recovery, interference, linearity and cross-reactivity. The identity of immunoreactive suPAR was confirmed by size-exclusion HPLC. To establish anatomical sites of release and uptake, we measured suPAR in regional samples from subjects undergoing cardiac catheterization. RESULTS: The median concentration of suPAR was 2.1 ng/mL (IQR:1.7-2.3) in health. In comparison with EDTA, suPAR measurements were affected by lithium heparin (>10% change) and increased with serum usage. suPAR reactivity also increased in the presence of haemolysis (10 g/L), but was suppressed with urokinase and lipids (4 g/L). In multiple regression analyses, suPAR associated independently with body weight, NT-proBNP and MR-proADM (P = .03) for healthy individuals. Regional plasma sampling showed lower suPAR concentrations in the coronary sinus and renal vein compared with concentrations in femoral arterial samples. Immunoreactive circulating suPAR species had Mr of 10-39 kDa. CONCLUSION: The suPARnostic® assay performs acceptably for a clinical assay but is limited in the presence of high levels of hemolysis, lipids and urokinase. We provide the first evidence for the heart and kidneys as organs of suPAR clearance in humans. Additional investigations are warranted to determine whether there is a need to compare the marker performance of differing circulating forms of suPAR.

The performance of contemporary cystatin C-based GFR equations in predicting gentamicin clearance.

AIMS: We aimed to compare the performances of contemporary cystatin C (Cys)-based GFR equations, and the creatinine only Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for predicting gentamicin clearance. METHODS: The bias and imprecision of the CKD-EPI, CKD-EPI_Cys and creatinine-cystatin C CKD-EPI (CKD-EPI_CrCys) equations for predicting gentamicin clearances, were assessed in 260 patients treated with gentamicin during 2012-2013. The creatinine-cystatin C Berlin Initiative Study equation (BIS_CrCys) was examined in the ≥70 year subgroup. The reference gentamicin clearance was calculated using post-dose plasma concentrations. RESULTS: The CKD-EPI_CrCys equation had the highest percentage of estimates within 30% of the reference gentamicin clearance (70%, P = 0.003) and lowest root mean square error (95% CI) of 29 (25, 23) ml min(-1) of the three equations for the entire cohort. There was no significant improvement in the performances of the equations with the exclusion of 41 patients with abnormal thyroid function tests or steroid co-prescription at the time of the index gentamicin dose. Of the remaining 219 patients, adjustment for individual BSA improved the performances of all GFR equations (P ≤ 0.003) in those with body mass indices (BMI) <18.5 or ≥30 kg m(-2) , but not those with BMI 18.5-29.9 kg m(-2) . There was no advantage of the BIS_CrCys over the CKD-EPI_CrCys equation in the ≥70 year subgroup. CONCLUSIONS: The CKD-EPI_CrCys equation provided the best estimate of gentamicin clearance. If used for guiding gentamicin dosing, the results from GFR equations should be adjusted for individual BSA at the extremes of body size.

Comparative performances of the new chronic kidney disease epidemiology equations incorporating cystatin C for use in cancer patients.

AIM: In cancer patients receiving chemotherapy treatment, accurate assessment of kidney function is required. The aim of our study was to investigate whether the inclusion of cystatin C together with creatinine in prediction equations would improve the prediction of glomerular filtration rate (GFR). METHODS: Plasma creatinine and cystatin C were analyzed in 155 patients (cancer, n = 80, kidney donors, n = 75) undergoing (99m) Technetium diethylenepentaacetic (Tc-DTPA) GFR clearance. Equations by the CKD-EPI (chronic kidney disease epidemiology) group (creatinine-, creatinine + cystatin C-, cystatin C-based, respectively) and Cockcroft-Gault were compared with Tc-DTPA GFR by difference plots, receiver operator characteristics curve analysis, root mean square error, chi-squared analysis and percentage concordance according to carboplatin dosage. Comparisons between two creatinine methodologies (enzymatic vs Jaffe) were also performed. RESULTS: In the overall group, the combination creatinine and cystatin C equation had 69% of results within 20% of GFR (P20), a sensitivity of 86.3% and a specificity of 73.1% to detect reduced GFR at <90 mL/min/1.73 m(2), and a concordance of 78%. In contrast, the traditional Cockcroft-Gault equation had a P20 of 38.0%, with a large underestimation to predict GFR, thereby accounting for approximately 45% of dosing discordance. No obvious differences were obtained when comparing the performance of equations using the two creatinine methodologies. CONCLUSION: The inclusion of cystatin C in the CKD-EPI equations improved the prediction of kidney function in the overall population, although probably not sufficiently for it to be favored over radioisotopic GFR for guiding chemotherapy. More research is warranted to further improve estimated GFR equations for these purposes.

The relative effects of fat versus muscle mass on cystatin C and estimates of renal function in healthy young men.

BACKGROUND: It is well known that plasma creatinine concentration is affected by muscle mass, while some studies have suggested cystatin C is affected by body mass index (BMI). Our aim was to assess the effects of lean versus fat mass on cystatin C and creatinine derivative equations in estimating glomerular filtration rate (GFR) in healthy young men. METHODS: Three groups of participants were studied: those classified as normal (BMI 18-25 kg/m(2) with body fat <30%); muscular subjects (BMI >30 kg/m(2) and body fat <20%); and obese subjects (BMI >30 kg/m(2) and body fat >30%). All underwent diethylenetriamine pentaacetic acid GFR, bio-electrical impedance and dual-energy X-ray absorptiometry body composition analysis, measurement of plasma cystatin C, creatinine and high-sensitivity C-reactive protein and completed a diet record. RESULTS: Cystatin C was highest in the obese group (0.77 mg/L; 95% confidence intervals [CI] 0.69-0.77) and creatinine was highest in the muscular group (90.1 µmol/L; 95% CI 84.3-96.0). On multivariate analysis, body fat and GFR (P = 0.003) were significant determinants of cystatin C; muscle mass and age affected creatinine significantly (P = 0.02). Using cystatin C equations, Le Bricon and Hoek showed significantly lower estimated GFR in the obese group but performed reasonably well within 50%, 30% and 20% of GFR. Creatinine equations showed significant underestimations of GFR for the muscular group. CONCLUSIONS: Body fat is a significant determinant of cystatin C while creatinine concentration is highly affected by muscle mass and age. Body composition plays an important role in the interpretation of renal function. Cystatin C equations are still accurate in predicting GFR in our healthy male group without chronic kidney disease.

Methods of Estimating GFR - Different Equations Including CKD-EPI.

The initiative for estimating glomerular filtration rate (GFR) derives from the limitations of interpreting plasma creatinine alone, the cost and complexities of determining a gold standard GFR with either inulin or radionuclides, and the inaccuracies inherent in measuring a 24 h urine creatinine clearance. In August 2005, the Australasian Creatinine Consensus Working Group recommended that an eGFR based on the abbreviated MDRD (Modification of Diet in Renal Disease) formula shall be automatically calculated for every request for creatinine in people over 18 years. Uptake was almost universal, though with appropriate caveats in place regarding potential limitations. Updated recommendations in 2007 recognised uniform standardisation of the plasma creatinine assay. A recent development is the CKD-Epidemiology Collaboration (CKD-EPI) equation which confers less underestimation of GFR in subjects with normal renal function. Cystatin C and its derivative equations may have advantages in some situations.