Monitoring of Eosinophil Derived Proteins by Microsampling Bioanalysis for Disease Monitoring

Microsampling is the act of taking small volume (< 100 µL) blood samples for bioanalytical applications. Blood samples can be taken remotely and by a non-clinical specialist (i.e. a patient at home), despatched to central laboratories, and analysed by bioanalytical detection techniques such as liquid chromatography mass spectrometry (LC-MS) and enzyme linked immunosorbent assay (ELISA). The development of microsampling techniques has opened up novel approaches to delivering healthcare remotely.
Eosinophils are a form of granulocyte that are involved in several inflammatory processes and host response against infection. The role of eosinophils in asthma has been extensively studied, with evidence suggesting that they are involved in many aspects of asthma pathogenesis. Eosinophil cell count has been used as a biomarker for diagnosis and therapeutic response in several instances, e.g. response to inhaled corticosteroids. The question is therefore asked as to whether eosinophils can be monitored via a microsampling device. Though microsampling devices have been applied to a wide range of small and large molecule analytes encompassing pharmaceuticals and associated metabolites, endogenous metabolites, and protein biomarkers, it is challenging to investigate applications where the cell itself is a biomarker. Typically, this is due to the drying of the blood sample onto the microsampling device resulting in cell lysis.
LC-MS based proteomics has been previously applied to the study of eosinophils, with several proteins being found in high abundance. These include proteins which are thought to be unique to eosinophils (eosinophil peroxidase (EPX), major basic protein 2 (MBP2)). It is suggested therefore, that these proteins could potentially be used as a surrogate marker of eosinophil count due to their high specificity for the eosinophil. This has been previously demonstrated for EPX in sputum, whereby eosinophil count correlated with EPX concentration in the same matrix. Despite this, further study is required to investigate whether EPX correlates strongly with eosinophil count in blood, and further, whether this can be replicated on a dried blood microsample.