Recent studies showed that pro-brain natriuretic peptide (proBNP)-108 and N-terminal proBNP-76 (NT-BNP) contains seven sites for O-linked oligosaccharide attachment. The levels of glycosylated NT-BNP are underestimated, because in NT-BNP assay system, one antibody recognizes NT-BNP [42–46], which contains glycosylation sites at amino acid residues 44. A recent study showed that O-linked oligosaccharide attachment almost completely inhibits the binding of the antibody to the peptide. In this study we investigate the pathophysiological significance of plasma levels of non-glycosylated (nonglyNT-BNP) and glycosylated NT-BNP (glyNT-BNP) in heart failure (HF) and chronic renal failure (CRF).Design and Method:
We enrolled 219 patients with HF and 142 patients with CRF on haemodialysis. To measure nonglyNT-BNP and glyNT-BNP, samples were incubated with or without a cocktail of deglycosylating enzymes, and NT-BNP was measured using Roche Elecsys proBNP II. The percentage glyNT-BNP was calculated as glyNT-BNP/(glyNT-BNP + nonglyNT-BNP).Results:
BNP is 271 ± 586 pga/mL, and nonglyNT-BNP is 2920 ± 21035 pg/mL in HF, whereas BNP is 384 ± 660 pga/mL, and nonglyNT-BNP is 7485 ± 11909 pg/mL in CRF. NonglyNT-BNP/BNP ratio in CRF is higher than that in HF (31.8 ± 51.6 vs 7.5 ± 8.4, P < 0.001). Interestingly, the percentage glyNT-BNP in CRF is also higher than that in HF (82.7 ± 6.8 vs 63.1 ± 13.7, P < 0.01), suggesting that > 80% of total NT-BNP in CRF and >60% of total NT-BNP in HF are invisible to the assay and therefore underestimated. There are significant relationships between the percentage glyNT-BNP and NT-BNP/BNP ratio in HF (r = -0.449, P < 0.001) and CRF (r = -0.498, P < 0.001). After haemodialysis (n = 66), plasma BNP and nonglyNT-BNP declined (p < 0.001); however, glyNT-BNP was unchanged. Notably, the percentage glyNT-BNP was increased after haemodialysis (81.7 ± 6.6 to 84.6 ± 6.1, p < 0.001).Conclusions:
These findings suggest that most endogenous plasma NT-BNP is glycosylated and therefore undetectable with the current NT-BNP assay system (Roche Elecsys proBNP II), and that the relative glycosylation level is increased by haemodialysis.