A specific calprotectin neo-epitope (CPa9-HNE) in serum from inflammatory bowel disease patients is associated with neutrophil activity and endoscopic severity

Background and aims: Endoscopy and the use of fecal calprotectin (fecal CP) are among the least favored methods for assessing disease activity by inflammatory bowel disease (IBD) patients; the handling/processing of fecal samples is also impractical. Therefore, we sought to develop a novel neo-epitope serum calprotectin ELISA, CPa9-HNE, with the aim of quantifying neutrophil activity and NETosis and proposing a non-invasive method for monitoring disease activity in IBD patients. Methods: In vitro cleavage was performed by mixing calprotectin (S100A9/S100A8) with human neutrophil elastase (HNE), and a novel HNE-derived calprotectin neo-epitope (CPa9-HNE) was identified by mass spectrometry for ELISA development. The CPa9-HNE ELISA was quantified in supernatants from ex vivo activated neutrophils and serum samples from patients with ulcerative colitis (UC, n = 43), Crohn’s disease (CD, n = 93), and healthy subjects (HS, n = 23). For comparison, fecal CP and MRP8/14 biomarkers were also measured. Results: CPa9-HNE was specific for activated neutrophils ex vivo. Serum CPa9-HNE levels were four fold higher in CD (p