Journal
CLINICA CHIMICA ACTA
Volume 413, Issue 3-4, Pages 483-489Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.cca.2011.11.007
Keywords
'Top-down' protein mass spectrometry; Retinol-Binding Protein; Retinol-Binding Protein 4; Tubular proteinuria; Renal Fanconi Syndrome; Dissociation-enhanced lanthanide fluorescence immunoassay
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Funding
- Cambridge Biomedical Research Centre
- Addenbrooke's Hospital Charities
- Bart's
- London Charity
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Background: Retinol-Binding Protein in urine (uRBP), a biomarker for the proximal renal tubular disease of congenital and acquired Fanconi Syndrome (FS) occurs in multiple forms. However these have not had quantitative mass spectrometric (MS) analysis, nor is there a validated assay for defined molecular species of uRBP with linearity on sample dilution. Methods: A 'Top-down' MS approach identified distinct forms of uRBP differing by only one amino acid. Based on this, we designed a dual-monoclonal antibody-based fluorescence immunoassay calibrated with intact plasma RBP4. Results: LC-MS showed that uRBP in FS (one Dent disease urine) comprised intact plasma RBP4 and C-terminal-truncated RBP4, desL-RBP4 and desLL-RBP4 in molar ratio 2:2:1. DELFIA (R) assay calibrated with plasma RBP4, formulated with two monoclonal antibodies (HyTest, Finland), mAb48 for capture and biotinylated-mAb42 for detection, provided good sensitivity (1 mu g/L), working range>500 mu g/L and good linearity on sample dilution. The three predominant forms of uRBP were equipotent over the assay working range. uRBP reference range was <3 mu g/mmol creatinine and FS patients had concentrations of 1000-5000 mu g/mmol creatinine. Conclusions: Using 'Top-down' MS analysis of uRBP we devised an accurate, linear, fluorescence immunoassay with defined RBP molecular targets optimal for uRBP measurement. Discrimination of elevated uRBP from the upper limit of normal was some 10-fold greater than previous assays. (C) 2011 Elsevier B.V. All rights reserved.
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