Abstract
There is an emerging interest in the diverse functions of neutrophil extracellular traps (NETs) in a variety of disease settings. However, data on circulating NETs rely largely upon surrogate NET markers such as cell-free DNA, nucleosomes, and NET-associated enzymes. Citrullination of histone H3 by peptidyl arginine deiminase 4 (PAD4) is central for NET formation, and citrullinated histone H3 (H3Cit) is considered a NET-specific biomarker. We therefore aimed to optimize and validate a new enzyme-linked immunosorbent assay (ELISA) to quantify the levels of H3Cit in human plasma. A standard curve made of in vitro PAD4-citrullinated histones H3 allows for the quantification of H3Cit in plasma using an anti-histone antibody as capture antibody and an anti-histone H3 citrulline antibody for detection. The assay was evaluated for linearity, stability, specificity, and precision on plasma samples obtained from a human model of inflammation before and after lipopolysaccharide injection. The results revealed linearity and high specificity demonstrated by the inability of detecting non-citrullinated histone H3. Coefficients of variation for intra- and inter-assay variability ranged from 2.1 to 5.1% and from 5.8 to 13.5%, respectively, allowing for a high precision. Furthermore, our results support an inflammatory induction of a systemic NET burden by showing, for the first time, clear intra-individual elevations of plasma H3Cit in a human model of lipopolysaccharide-induced inflammation. Taken together, our work demonstrates the development of a new method for the quantification of H3Cit by ELISA that can reliably be used for the detection of NETs in human plasma.
Highlights
Neutrophil extracellular traps (NETs) are webs of chromatin fibers (DNA and histones) coated with antimicrobial granular proteins including the enzymes neutrophil elastase (NE) and myeloperoxidase (MPO)
As no international standard preparation is available for H3Cit, we generated a standard curve using in vitro PAD4citrullinated H3Cit, as previously described [24]
For the first time, an elevation of H3Cit in plasma in a human model of LPS-induced inflammation
Summary
Neutrophil extracellular traps (NETs) are webs of chromatin fibers (DNA and histones) coated with antimicrobial granular proteins including the enzymes neutrophil elastase (NE) and myeloperoxidase (MPO). In light of the emerging data on the adverse role of NETs, pre-clinical studies are starting to explore the possibility of alleviating the effects of NETs with new therapeutic agents that degrade NETs or inhibit their formation [3, 8, 20]. In this context, a reliable and specific biomarker of NETs would play a central role in prediction of risk, prognosis, and therapeutic effects
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