Towards stable diagnostic setups in clinical proteomics: Absolute quantitation of peptide biomarkers using MALDI-TOF-MS

In routine clinical diagnostics, peptide biomarkers are most commonly quantified using immunological techniques but these methods often lack sensitivity and/or specificity. Hence, quantitative mass spectrometry detection is desirable as an alternative diagnostic tool. To date, quantitative mass spectrometry is mostly based on ESI-MS coupled to LC, requiring highly sophisticated instrumentation and knowledge and is time consuming and expensive. In contrast, MALDI-TOF-MS is a very simple, sensitive and rapid method for the detection of peptide biomarkers. However, the infeasibility of absolute quantification has been a tremendous handicap to the use of MS in stable clinical diagnostics. Here, we describe the development of a technical platform based on ClinProt particles and heavy-isotope internal peptide standards for the fast and reliable preparation of samples. This combines the advantages of MALDI-TOF as a read-out system with absolute quantitation of peptide biomarkers. As a proof-of-concept, this platform was successfully employed for the absolute determination of the concentration of the highly abundant serum peptide des-Ala-Fibrinopeptide A in 45 serum samples from healthy donors. Such technology essentially contributes to the development of a stable MALDI-TOF-MS-based clinical assay.