Point of care measurement of eosinophil derived neurotoxin (EDN) as a biomarker of eosinophilic asthma

Abstract

Introduction: Increased blood eosinophils (EOS) are associated with increased exacerbations, disease severity and mortality in asthma, and therapeutic reduction of EOS is beneficial to these patients (J. Nixon Pharmacology & Therapeutics 2017). EDN is an alternative biomarker of eosinophilia that may better reflect eosinophil activity than EOS. EDN can be measured by immunoassay but a clinical diagnostic is not available. We developed a novel point of care (PoC) EDN diagnostic and deployed in a pilot study. Methods: Venous plasma and haematology samples and fingerprick capillary blood were collected from 10 asthmatic patients. EOS were measured by standard clinical haematology. EDN was measured in whole venous and capillary blood and plasma using a prototype PoC diagnostic, and also in plasma by a commercially available sandwich ELISA assay (Alpco). Results: EOS ranged from 60 to 1220 cells/uL. EDN levels in plasma, venous and capillary blood measured with the novel diagnostic, and in plasma with the Alpco assay, ranged from 3.4 – 23.0, 2.4 - 15.9, 3.4 - 26.9, and 4.28 to 25.2 ng/mL respectively. All 4 EDN measurements were highly correlated with EOS, with Pearson r values of 0.88, 0.86, 0.84 and 0.77, and P values of 0.0007, 0.0012, 0.0025 and 0.016 respectively. Conclusions: EDN levels can be measured in asthmatics and are highly correlated with eosinophils. EDN may be an alternative biomarker of eosinophilic asthma to EOS and is amenable to rapid PoC diagnostic technology. EDN merits further investigation as a potential predictive biomarker for therapies directed at eosinophilic asthma patients.