Poster in AACC 2010: B-type natriuretic peptide measurements by two assays utilizing antibodies with different epitope specificity

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B-type natriuretic peptide measurements by two assays utilizing antibodies with different epitopes

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Natalia N. Tamm ¹, Alexander G. Semenov ¹, Karina R. Seferian ¹, MaryAnn M. Murakami ², Fred S. Apple ², Ekaterina V. Koshkina ³, Michail I. Krasnoselsky ⁴, Roman V. Malanichev ⁵,
Alexander G. Arutyunov ⁶, Alexey G. Katrukha ¹.

Brain natriuretic peptide (BNP) is an acknowledged marker of heart failure (HF) and is widely used in clinical practice for HF diagnosis and patient management. Most commercial BNP assays are designed as a sandwich-type immunoassays utilizing two monoclonal antibodies (MAbs) specific to two the different epitopes. At least one of these two antibodies is specific to the ring structure of the BNP molecule, while the other is specific either to the N-terminus or to C-terminus of the peptide. All commercial BNP assays cross-react with the proBNP forms (nonglycosylated and glycosylated), but the rate of cross-reactivity varies among assays.
It was shown recently that HF patients plasma contains a small portion of the fulllength BNP form (BNP-32) along with multiple forms truncated from both the N- (BNP 3-32, 4-32, 5-32) and C-termini (BNP 5-31, 1-25, 1-26) (Niederkofler et al, 2008). So it could be expected that BNP measurements by current versions of commercial assays could be affected by proteolytic degradation. Recently we have reported a new type of BNP assay - “Single Epitope Sandwich assay” (SES assay) (Tamm et al, 2008), in which one MAb 24C5 is specific ring fragment of the BNP molecule (epitope 11-17) and the second MAb – Ab-BNP2 recognizes the immune complex of MAb 24C5 with BNP (proBNP) only. Thus, only one epitope, located in the relatively stable part of the BNP molecule is needed for BNP measurements in the SES assay. This feature gives a substantial advantage for the SES assay approach over conventional assays because truncated BNP (or proBNP) forms presented in patients’ blood could be also detected by the SES assay.
The aim of this study was to compare results of BNP measurements by the SES assay and by the conventional-type Siemens ADVIA Centaur BNP immunoassays in order to verify hypothesis according to which SES assay should detect more BNP in the sample than conventional-type immunoassay.

Conclusions:
Precise measurements of BNP values are required for the correct diagnosis of patients with the signs and symptoms of HF. The underestimation of BNP/proBNP concentrations due to analyte proteolytic degradation may result in the misdiagnosis and/or misclassification of patients.
The SES assay is able to detect BNP molecules partially truncated from the both termini, thus detecting more molecules in the sample than the conventional-type assay. Further clinical studies are still needed to determine the implications of using the SES assay for the diagnosis, management and outcomes assessment of HF patients.