Screening of serological markers for differential diagnosis ischemic colitis and ulcerative colitis by proteomic techniques

Objective To screen and identify serum protein biomarkers for the differential diagnosis between ischemic colitis (IC) and ulcerative colitis (UC) by tandem mass tag (TMT) combined with liquid chromatography/tandem mass spectrometry (LC-MS/MS). Methods From January 2018 to January 2019, at the First Affiliated Hospital of School of Medicine of Zhejiang University, patients with UC or IC, and health controls, each 10 cases, were enrolled into UC group, IC group and normal control (NC) group, respectively. Fasting serum samples of all the subjects were collected. After removal of high-abundance protein, followed by proteolysis, peptide labeling and fractionating, the samples were then processed by mass spectrometry. The protein with TMT data of three groups was obtained and protein with TMT value 0 were removed. Heat map of protein was constructed. The differential protein was defined as the protein fold change over 1.5 or less than 0.67. The Reactome database was used to cluster the pathways of differential proteins among groups. Statistical methods included t test, hypergeometry test and corrected by BH multiple test. Results A total of 357 serum proteins were identified by proteomic profiling. There were 27 differential proteins between the IC group and the NC group, including six up-regulated proteins and 21 down-regulated proteins. There were 228 differential proteins between the UC group and the NC group, including 75 up-regulated proteins and 153 down-regulated proteins. There were 49 differential proteins between UC group and IC group, including 22 up-regulated proteins and 27 down-regulated proteins. In the comparison of differential proteins between the NC group, IC group and UC group, only the expression of fibrin 3 was statistically significant (the fold change between UC and NC, between UC and IC, between IC and NC were 0.24, 0.46 and 0.53, respectively; t=-5.089, -7.298 and -3.919, all P<0.01). The results of pathway cluster analysis showed that in the comparison of differential proteins between IC group and NC group, only the platelet degranulation pathway was enriched, and 10 proteins were involved in this pathway (P<0.01). In the comparison of differential proteins between UC group and NC group, there were 58 pathways enriched, of which 38 proteins were involved in the platelet degranulation pathway, 16 proteins were involved in the initial complement trigger pathway, 13 proteins were involved in the complement cascade pathway, and 11 proteins were involved in antibody-mediated complement activation pathway (all P<0.01). In the comparison of differential proteins between UC group and IC group, three different pathways were obtained. Among them, nine proteins were involved in the platelet degranulation pathway, seven proteins were involved in the initial complement trigger pathway, and five proteins were involved in the complement cascade pathway (all P<0.01). Conclusions The difference in serum proteome between IC patients and UC patients was significant, and the differential proteins are mainly involved in platelet activation and complement activation. The candidate proteins identified in this study may be used as biomarkers for the differential diagnosis of UC and IC in the future. Key words: Colitis, ischemic; Colitis, ulcerative; Proteomics; Markers, serum