Analytical assay characterization for 1–108Pro-B-type natriuretic peptide on the BioPlex™ 2200 analyzer

Specificity of B-Type Natriuretic Peptide Assays: Cross-Reactivity with Different BNP, NT-proBNP, and proBNP Peptides

BACKGROUND

B-type natriuretic peptides (BNPs) are used clinically to diagnose and monitor heart failure and are present in the circulation as multiple proBNP-derived fragments. We investigated the specificity of BNP immunoassays with glycosylated and nonglycosylated BNP, N-terminal proBNP (NT-proBNP), and proBNP peptides to probe the cross-reactivity of each assay.

METHODS

Nine B-type natriuretic peptides were studied,including synthetic and recombinant BNP (Shionogi, Scios, Mayo), human and synthetic glycosylated and nonglycosylated NT-proBNP (HyTest, Roche Diagnostics), and human glycosylated and nonglycosylated proBNP (HyTest, Scios). Five BNP [Abbott, Abbott POC, Alere, Beckman Coulter, Siemens (Centaur)], 9 NT-proBNP [Ortho-Clinical Diagnostics, Roche, Response, bioMerieux, Siemens (Dimension, Immulite, Stratus CS), Mitsubishi] and 3 research-use-only proBNP immunoassays [Biosite (Alere), Bio-Rad, Goetze] were evaluated. Specificity was assessed by calculating the recovery between baseline and peptide-spiked human plasma pools at target concentrations of 100 ng/L BNP, 300 ng/L proBNP, or 450 ng/L NT-proBNP. All assays were performed in duplicate.

RESULTS

BNP and NT-proBNP assays demonstrated substantial cross-reactivity with proBNP peptides. NT-proBNP assays do not detect glycosylated forms of either NT-proBNP or proBNP. proBNP assays preferentially detect the BNP 1-32 peptide and have minimal cross-reactivity with BNP peptides and glycosylated proBNP.

CONCLUSIONS

BNP or NT-proBNP results are not transferable among the current existing immunoassays owing to their differences in cross-reactivity and ability to detect various glycosylated forms of proBNP-derived fragments. Opportunities remain to standardize and harmonize BNP and NT-proBNP assays, as well as to develop specific proBNP assays, to widen their clinical scope of use.

State of the art of immunoassay methods for B-type natriuretic peptides: An update

The aim of this review article is to give an update on the state of the art of the immunoassay methods for the measurement of B-type natriuretic peptide (BNP) and its related peptides. Using chromatographic procedures, several studies reported an increasing number of circulating peptides related to BNP in human plasma of patients with heart failure. These peptides may have reduced or even no biological activity. Furthermore, other studies have suggested that, using immunoassays that are considered specific for BNP, the precursor of the peptide hormone, proBNP, constitutes a major portion of the peptide measured in plasma of patients with heart failure. Because BNP immunoassay methods show large (up to 50%) systematic differences in values, the use of identical decision values for all immunoassay methods, as suggested by the most recent international guidelines, seems unreasonable. Since proBNP significantly cross-reacts with all commercial immunoassay methods considered specific for BNP, manufacturers should test and clearly declare the degree of cross-reactivity of glycosylated and non-glycosylated proBNP in their BNP immunoassay methods. Clinicians should take into account that there are large systematic differences between methods when they compare results from different laboratories that use different BNP immunoassays. On the other hand, clinical laboratories should take part in external quality assessment (EQA) programs to evaluate the bias of their method in comparison to other BNP methods. Finally, the authors believe that the development of more specific methods for the active peptide, BNP1-32, should reduce the systematic differences between methods and result in better harmonization of results.

Galectin-3 testing: validity of a novel automated assay in heart failure patients with reduced ejection fraction

Circulating levels of galectin-3 (Gal-3), a marker of cardiac fibrosis and remodeling, contribute to the risk stratification of patients with heart failure (HF). The aim of our study was to determine the analytical validity and clinical validity of a novel automated Gal-3 assay in HF patients with reduced ejection fraction. We showed an excellent agreement between the VIDAS® Gal-3 automated assay and the ELISA reference method (r=0.90, p<0.001) and a mean difference of -1.3 ng/mL was observed on the Bland and Altman plot. Gal-3 levels measured with the VIDAS® assay were significantly related to NYHA functional classes (p<0.001) and mean Gal-3 levels were 13.8 ng/mL in NYHA II patients, 17.7 ng/mL in NYHA III and 19.6 ng/mL in NYHA IV. Furthermore, our results showed that Gal-3 levels measured with the VIDAS® assay were not only predictive of long-term cardiovascular death in patients with systolic HF but have also provided added value to natriuretic peptide testing in multimarker strategies. Therefore, our data are also supporting the clinical validity of the Gal-3 automated assay.

Value of proBNP1-108 testing for the risk stratification of patients with systolic heart failure

The study objectives were to determine the circulating levels of proBNP1-108, the precursor of B-type natriuretic peptide (BNP) and amino-terminal pro-BNP (NT-proBNP), in patients with systolic heart failure (HF) and to assess their prognosis value for cardiovascular (CV) death over a long-term follow-up. Seventy-three patients with systolic HF and 68 healthy volunteers were included. ProBNP1-108, BNP and NT-proBNP levels were measured with automated immunoassays and their predictive value for long-term survival was assessed through an 8 years follow-up. ProBNP1-108 levels were markedly increased in patients with systolic HF in comparison to healthy volunteers. In univariate proportional hazard model, survival was related to proBNP1-108, BNP, NT-proBNP, age, EF and glomerular filtration rate (eGFR). Kaplan-Meier survival curves according to proBNP tertiles diverged significantly, and the highest proBNP levels were related to patients with the highest risk of CV death. In a multivariate analysis including age, EF, proBNP1-108, BNP, NT-proBNP, and eGFR levels, NT-proBNP was the strongest predictor of long term CV death. Our study therefore demonstrated that high levels of proBNP1-108, measured with an assay with enhanced analytical specificity, are related to the long-term risk of cardiovascular death in systolic heart failure.

Circulating forms of the b-type natriuretic peptide prohormone: pathophysiologic and clinical considerations

Recent studies reported that many different biochemical forms of B-type-related peptides circulate in human blood. In particular, a significant amount of the prohormone peptide (i.e., proBNP108) can be detected in plasma of patients with heart failure. These data indicate that the posttranslational maturation processing of the B-type natriuretic peptide (BNP) precursor may not be efficient in heart failure. The aim of this chapter is to describe the biochemical pathways of proBNP108 maturation and to discuss the pathophysiological relevance of alteration of the posttranslational maturation mechanisms in heart failure. An impaired cardiac endocrine function was proposed to explain the altered electrolyte and fluid homeostasis occurring in chronic heart failure. Recent studies demonstrated that a great part of BNPs assayed by immunoassay methods in healthy subjects and in patients with cardiovascular disease is devoid of biological activity. These findings suggest that an alteration in posttranslational maturation of BNP precursor may promote the resistance to biological action of BNP in patients with heart failure at a prereceptor level. These studies also open a new and more complex scenario regarding the circulating BNPs. The active hormone (i.e., BNP1-32) may be produced even in vivo from the circulating precursor proBNP108 by plasma enzyme degradation, such as the soluble form of corin, possibly able to process the circulating intact precursor of natriuretic hormones. As a future perspective, the simultaneous measurement of the proBNP1-108 and the active peptide BNP1-32 with more specific methods could allow a more accurate estimation of both production/secretion of B-type-related peptides from cardiomyocytes and the true activity of the cardiac endocrine function.