Analysis by Clinical Mass Spectrometry of Bloodstains

Analyses of blood spotted and dried on a matrix (DBS), has been used since the 1960s in clinical chemistry neonatal screening. Since then, many clinical analytes, including nucleic acids, small molecules and lipids, have been successfully measured using DBS.

DBS collection is in fact less invasive than classical venous puncture, it can be carried out by the patient at home and shipped by regular mail with no particular risk of contamination. The use of DBS in routine for the detection of transmissible diseases, as well as for the follow-up of chronic disease like diabetes, represent a safer and less costly evolution of clinical biology for the society.

However the routine use of DBS is yet is limited. The major limitations of using DBS are represented by the small blood volumes associated with DBS sampling (5-10 μL) and by the limited possibility to detect peptides and proteins.

In this program, we will address this issue by adapting to DBS mass spectrometry (MS) quantification of proteins/peptides. This relies on the detection of distinctive proteotypic peptides (peptides which sequence is specific to a unique protein). The specificity of such assays using triple quadrupole mass spectrometer is based on the capability to detect peptides by three molecular characteristics: retention time, precursor ion mass (m/z) and fragment ion mass (m/z). The combination of the precursor ion mass and the fragment ion mass z, highly specific, is called a transition. This approach is named when several peptides are detected in a single run "multiple reaction monitoring" or MRM. Using this approach, the direct analysis of the trypsin digest of blood samples is possible without additional sample fractionation.

In a series of preliminary experiments, we could detect on single DBS puch of 6mm of diameter, 35 plasma proteins. Several proteins are of clinical relevance such as apolipoprotein A, B, C, ceruloplasmin, haptoglobin, plasminogen, transthyretin (prealbumin) or serum albumin. We will extend the range of blood protein detected by MS. Focus will be put on select biomarkers to generate clinically relevant panels that can be used for patients monitoring, nutrition monitoring and for the follow-up of frailty in elderly people .

Innovative workflows to obtain more rapid, efficient and costless detection will be developed. We will also evaluate a new type of DBS card (Noviplex™) which collects plasma instead of whole blood, and is expected to achieve better clinical concordance of the results between DBS and classical sampling. The detection of the relevant clinical analytes will be validated on available patient samples in accordance with the clinical norm ISO15189 and the requirement for CE IVD marking. This will allow commercial developments (kits, protocols...) realized with the industrial partner Spot-to-lab. This start-up has already put on the market DBS analyses resulting from previous collaborative research. Being able to measure peptide/proteins from DBS in parallel with other clinical analytes also developed by Spot-To-Lab (vitamin D, HbA1c…) represents a breakthrough which will gives major perspective to the use of DBS in clinical chemistry for disease detection and monitoring.