Impact of Epitope Specificity and Precursor Maturation in Pro-B–Type Natriuretic Peptide Measurement

Natriuretic Propeptides as Markers of Atrial Fibrillation Burden and Recurrence (from the AMIO-CAT Trial)

Natriuretic peptides are established plasma markers of systolic heart failure, but their usefulness for the evaluation of atrial fibrillation (AF) is unknown. We examined mid-regional pro-atrial natriuretic peptide (MR-proANP) and N-terminal pro-brain natriuretic peptide (NT-proBNP) in patients undergoing ablation for AF. A subpopulation of 102 patients (median age 60 [52;65], 82% male) from the AMIO-CAT trial (Recurrence of arrhythmia following short-term oral AMIOdarone after CATheter ablation for atrial fibrillation: a double-blind, randomized, placebo-controlled study) undergoing ablation for paroxysmal (n = 55) or persistent (n = 47) AF was studied. MR-proANP and NT-proBNP were measured before ablation and at 1, 3, and 6 months' follow-up. Three-day Holter monitoring was performed before ablation, and 6 to 8 weeks and 6 months after ablation. Plasma MR-proANP and NT-proBNP concentrations were higher during AF than during sinus rhythm before ablation (188 pmol/L [131;260] vs 94 pmol/L [64;125], p <0.001; 78 pmol/L [43;121] vs 10.3 pmol/L [5.9;121], p <0.001) and at 1, 3, and 6 months' follow-up. Categories of AF burden on 3-day Holter monitoring (0%, 0% to 99%, and 99% to 100%) were associated with plasma concentrations of both MR-proANP (94 pmol/L [55;127] vs 117 pmol/L [88;185] vs 192 pmol/L [127;261], p <0.001) and NT-proBNP (10 pmol/L [5.9;22] vs 22 pmol/L [8.9;53] vs 81 pmol/L [45;116], p <0.001). In a multivariate regression analysis, however, there was no significant association between baseline propeptide concentrations and recurrence of AF at 6 months' follow-up. In conclusion, AF was associated with higher plasma concentrations of MR-proANP and NT-proBNP than sinus rhythm. Moreover, AF burden was associated with subsequent concentrations of both MR-proANP and NT-proBNP. The results suggest that natriuretic propeptide measurement reflects functional cardiac dysfunction during AF, and that AF burden should be included in biochemical assessment of left ventricular dysfunction.

Unraveling the Molecular Complexity of O-Glycosylated Endogenous (N-Terminal) pro-B-Type Natriuretic Peptide Forms in Blood Plasma of Patients with Severe Heart Failure

BACKGROUND

Currently, N-terminal pro-B-type natriuretic peptide (NT-proBNP) and its physiologically active counterpart, BNP, are most frequently used as biomarkers for diagnosis, prognosis, and disease monitoring of heart failure (HF). Commercial NT-proBNP and BNP immunoassays cross-react to varying degrees with unprocessed proBNP, which is also found in the circulation. ProBNP processing and immunoassay response are related to O-linked glycosylation of NT-proBNP and proBNP. There is a clear and urgent need to identify the glycosylation sites in the endogenously circulating peptides requested by the community to gain further insights into the different naturally occurring forms.

METHODS

The glycosylation sites of (NT-) proBNP (NT-proBNP and/or proBNP) were characterized in leftovers of heparinized plasma samples of severe HF patients (NT-proBNP: >10000 ng/L) by using tandem immunoaffinity purification, sequential exoglycosidase treatment for glycan trimming, β-elimination and Michael addition chemistry, as well as high-resolution nano-flow liquid chromatography electrospray multistage mass spectrometry.

RESULTS

We describe 9 distinct glycosylation sites on circulating (NT-) proBNP in HF patients. Differentially glycosylated variants were detected based on highly accurate mass determination and multistage mass spectrometry. Remarkably, for each of the identified proteolytic glycopeptides, a nonglycosylated form also was detectable.

CONCLUSIONS

Our results directly demonstrate for the first time a rather complex distribution of the endogenously circulating glycoforms by mass spectrometric analysis in HF patients, and show 9 glycosites in human (NT-) proBNP. This information may also have an impact on commercial immunoassays applying antibodies specific for the central region of (NT-) proBNP, which detect mostly nonglycosylated forms.

Cardiac and proinflammatory markers predict prognosis in cirrhosis

BACKGROUND & AIMS

Inflammation and cardiac dysfunction plays an important role in the development of complications leading to increased mortality in patients with cirrhosis. Novel cardiac markers such as prohormone of ANP (proANP), copeptin and high-sensitivity troponin T (hs-TnT) and proinflammatory markers including soluble urokinase-type plasminogen activator receptor (suPAR) and high-sensitive C-reactive protein (hs-CRP) are related to these complications. We aimed to investigate if cardiac and proinflammatory markers are related to severity of liver disease, cardiac and haemodynamic changes, and long-term survival.

METHODS

One hundred and ninety-three stable cirrhotic patients (Child class: A = 46; B = 97; C = 50) had a full haemodynamic investigation performed with measurement of splanchnic and systemic haemodynamics and measurement of circulating levels of proBNP, proANP, copeptin, hs-TnT, LBP, IL 6, IL 8, IP 10, VEGF, hs-CRP and suPAR.

RESULTS

Soluble urokinase-type plasminogen activator receptor soluble urokinase-type plasminogen activator receptor, hs-CRP, and hs-TnT were significantly different throughout the Child classes (P < 0.01; P < 0.01; P < 0.02). All markers except copeptin correlated with indicators of disease severity in cirrhosis; ProANP and suPAR correlated with hepatic venous pressure gradient (r = 0.24 and r = 0.34; P < 0.001) and systemic vascular resistance (r = -0.24 and r = -0.33; P < 0.001). Cardiac (proANP, hs-TnT; P < 0.01) and proinflammatory (hs-CRP, suPAR; P < 0.05) markers were associated with mortality in a univariate Cox analysis, however, the strongest predictors of mortality in a multivariate Cox analysis were hs-TnT, ascites and hepatic venous pressure gradient (reg.coeff.: 0.34, P < 0.001; 0.16, P < 0.001; 0.06, P = 0.04).

CONCLUSION

Markers of cardiac dysfunction and inflammation are significantly associated with disease severity, degree of portal hypertension and survival in cirrhosis. In particular, hs-TnT and suPAR seem to contain prognostic information.

Effects of carvedilol and propranolol on circulatory regulation and oxygenation in cirrhosis: a randomised study

BACKGROUND AND AIMS

Newer studies suggest that carvedilol, a beta-blocker with a moderate anti-alpha-1 activity, is superior to propranolol in reducing the portal pressure and risk of variceal bleeding. The effect on arterial blood pressure is a matter of concern especially in decompensated patients.

AIMS

to assess potential differential effects of beta-blockers and beta-blockers with moderate anti-alpha-1 activity on selected haemodynamic, humoral, and respiratory characteristics in cirrhosis.

METHODS

Patients with cirrhosis and portal hypertension were randomised to receive carvedilol (n=16) or propranolol (n=13). Cardiac, systemic and splanchnic parameters along with oxygen saturation and plasma renin were measured at inclusion and after 3 months.

RESULTS

Arterial blood pressure, heart rate, and cardiac output decreased equally, central circulation time and systemic vascular resistance increased significantly but similarly. Central blood volume, plasma volume and arterial compliance were unaltered. The QTc interval and renin levels decreased in the carvedilol group, however not significantly different from the propranolol group. Arterial oxygen saturation and alveolar arterial oxygen gradient remained constant in both groups. Hepatic venous pressure gradient decreased equally in the carvedilol and propranolol groups (-17% and -20%, non significant).

CONCLUSIONS

Systemic haemodynamics and pulmonary effects of carvedilol and propranolol are modest and this study could not demonstrate any significant difference between the two treatments.

Glucagon-like peptide-1: effect on pro-atrial natriuretic peptide in healthy males

The antihypertensive actions of glucagon-like peptide-1 (GLP1) receptor agonists have been linked to the release of atrial natriuretic peptide (ANP) in mice. Whether a GLP1-ANP axis exists in humans is unknown. In this study, we examined 12 healthy young males in a randomized, controlled, double-blinded, single-day, cross-over study to evaluate the effects of a 2-h native GLP1 infusion. Plasma proANP concentrations were measured by an automated mid-region-directed proANP immunoassay and N-terminal pro B-type natriuretic peptide (BNP) on Roche Modular E170. Urine was collected for measurements of sodium excretion. Although GLP1 infusion increased the urinary sodium excretion markedly, there were no significant changes in either proANP or proBNP concentrations. When GLP1 infusion was stopped, sodium excretion declined rapidly. As proANP concentration reflects ANP secretion, our data could not confirm the existence of a GLP1-ANP axis in humans. Especially, the natriuretic effects of GLP1 seem unlikely to be mediated exclusively via ANP.

N-Terminal Pro–Atrial Natriuretic Peptide Measurement in Plasma Suggests Covalent Modification

BACKGROUND

The N-terminal fragment of cardiac-derived pro–B-type natriuretic peptide is a glycosylated polypeptide. It is unknown whether N-terminal pro–atrial natriuretic peptide (proANP) fragments are also covalently modified. We therefore evaluated the clinical performance of 2 distinctly different proANP assays on clinical outcome.

METHODS

We examined 474 elderly patients with symptoms of heart failure presenting in a primary healthcare setting. Samples were analyzed with an automated immunoluminometric midregion proANP (MR-proANP) assay and a new processing-independent assay (PIA) developed in our laboratory. The results were compared with Bland–Altman plots, and clinical performance was assessed by generating ROC curves for different clinical outcomes.

RESULTS

Despite linear regression results indicating a good correlation (r = 0.85; P &lt; 0.0001), the PIA measured considerably more proANP than the MR-proANP assay (mean difference, 663 pmol/L; SD, 478 pmol/L). In contrast, the clinical performances of the 2 assays [as assessed by the area under the ROC curve (AUC)] in detecting left ventricular dysfunction were similar [proANP PIA, 0.71 (95% CI, 0.63–0.79); MR-proANP assay, 0.74 (95% CI, 0.66–0.81); P = 0.32]. The prognostic ability to report cardiovascular mortality during a 10-year follow-up revealed AUC values of 0.66 (95% CI, 0.60–0.71) for the proANP PIA and 0.69 (95% CI, 0.63–0.74) for the MR-proANP assay (P = 0.08, for comparing the 2 assays).

CONCLUSIONS

Our data suggest that N-terminal proANP fragments in patient plasma differ from the calibrator peptides used but that the difference does not affect ROC curves in an elderly cohort of patients with mild to moderate heart failure. We suggest that human N-terminal proANP fragments can be covalently modified.

Practical application of natriuretic peptides in paediatric cardiology

It is still uncertain if cardiac natriuretic peptides are useful biomarkers in paediatric cardiology. In this review we identify four clinical scenarios in paediatric cardiology, where clinical decision-making can be difficult, and where we feel the paediatric cardiologists need additional diagnostic tools. Natriuretic peptide measurements could be that extra tool. We discuss and suggest N-terminal pro-B-type natriuretic peptide and B-type natriuretic peptide reference intervals for children without cardiovascular disease and cut-off points for the four specific paediatric heart conditions. We conclude that in premature neonates with persistent arterial ducts; in teenagers with tetralogy of Fallot and pulmonary regurgitation; and in children with heart transplants and potential allograft rejection cardiac peptides can provide the clinician with additional information, but in children with atrial septal defects the peptides are not helpful in guiding treatment or follow-up.