Application of the Spot method to the identification of peptides and amino acids from the antibody paratope that contribute to antigen binding.

Overlapping peptide scans prepared by Spot synthesis have been used to map interaction sites in several systems. Here we report our experience with this approach to identify peptides from the variable parts of anti-hapten, anti-peptide and anti-protein antibodies that retain their specific antigen-binding capacity in the Spot format. In general, the identification by the Spot method of antigen-reactive peptides was confirmed by using soluble peptides which demonstrated antigen-binding capacity in ELISA or Biacore and, biological activity for some peptides derived from anti-CD4 antibodies. The Spot method was also used to map precisely key residues from the antibody paratope. The identification of critical residues from an anti-troponin I antibody of diagnostic interest is reported as well as the compiled results from the analysis of five other antibodies of various specificities. A critical assessment of our results is provided by comparing results obtained by our approach in the mapping of antibody residues critical for antigen binding with data from the literature concerning the structural analysis of antigen-antibody complexes.

Local carotid atherosclerotic plaque proteins for the identification of circulating biomarkers in coronary patients.

OBJECTIVE: To identify circulating biomarkers that originate from atherosclerotic vulnerable plaques and that could predict future cardiovascular events. METHODS: After a protein enrichment step (combinatorial peptide ligand library approach), we performed a two-dimensional electrophoresis comparative analysis on human carotid plaque protein extracts (fibrotic and hemorrhagic atherosclerotic plaques). In silico analysis of the biological processes was applied on proteomic data. Luminex xMAP assays were used to quantify inflammatory components in carotid plaques. The systemic quantification of proteins originating from vulnerable plaques in blood samples from patients with stable and unstable coronary disease was evaluated. RESULTS: A total of 118 proteins are differentially expressed in fibrotic and hemorrhagic plaques, and allowed the identification of three biological processes related to atherosclerosis (platelet degranulation, vascular autophagy and negative regulation of fibrinolysis). The multiplex assays revealed an increasing expression of VEGF, IL-6, IL-8, IP-10 and RANTES in hemorrhagic as compared to fibrotic plaques (p<0.05). Measurement of protein expressions in plasmas from patients with stable and unstable coronary disease identified a combination of biomarkers, including proteins of the smooth muscle cell integrity (Calponin-1), oxidative stress (DJ-1) and inflammation (IL-8), that allows the accurate classification of patients at risk (p=0.0006). CONCLUSION: Using tissue protein enrichment technology, we validated proteins that are differentially expressed in hemorrhagic plaques as potential circulating biomarkers of coronary patients. Combinations of such circulating biomarkers could be used to stratify coronary patients.

Assay for measurement of intact B-type natriuretic peptide prohormone in blood.

BACKGROUND: B-Type natriuretic peptide (BNP1-32) as well as the N-terminal fragment of the prohormone containing residues 1-76 (NT-proBNP1-76), both cleavage products of the precursor proBNP1-108, are reported to be powerful markers for prognosis and risk stratification of heart failure. However, the intact precursor also circulates in the bloodstream. Assays for the detection of these cleavage products have been developed, but most of these assays may overestimate the concentrations of the cleavage products because they also measure the precursor form. It is therefore important to develop an immunoassay that specifically measures solely proBNP1-108 in plasma. METHODS: After carefully designing the peptide used to immunize mice, we selected a specific monoclonal antibody (mAb Hinge76) that recognizes the cleavage site of proBNP1-108, an epitope present only in the precursor form. mAb Hinge76 recognizes recombinant proBNP1-108 in a dose-dependent manner, without any significant cross-reactivity with either recombinant NT-proBNP1-76 or synthetic BNP1-32. By combining mAb Hinge76 with a polyclonal antibody directed against BNP1-32, we were able to set up a proBNP1-108-specific sandwich immunoassay able to confirm the presence of proBNP1-108 in blood samples. RESULTS: From a cohort of 50 healthy persons and 170 patients with congestive heart failure (CHF), our assay was able to differentiate healthy individuals from CHF patients (P <0.005). Interestingly, plasma proBNP1-108 concentrations were correlated with New York Heart Association classification. Moreover, a close relationship between proBNP1-108 and BNP1-32 concentrations may exist, as a good correlation (r2= 0.89) was obtained when their respective concentrations were compared. CONCLUSION: mAb Hinge76 is the first proBNP1-108-specific mAb produced that allows accurate estimation of proBNP1-108 concentrations in plasma.