The alleviative effect of C-phycocyanin peptides against TNBS-induced inflammatory bowel disease in zebrafish via the MAPK/Nrf2 signaling pathways

Ulcerative colitis (UC) is an incurable and highly complex chronic inflammatory bowel disease (IBD) affecting millions of people worldwide. C-phycocyanin (C-PC) has been reported to possess outstanding anti-inflammatory activities and can effectively inhibit various inflammation-related diseases. Whether C-PC-derived bioactive peptides can inhibit intestinal inflammation is worth research and consideration. The inhibition activities of three anti-neuroinflammatory peptides were evaluated using 2-4-6-trinitrobenzen sulfonic acid (TNBS)-induced zebrafish colitis model. Subsequently, the abilities of peptides to promote gastrointestinal motility were also examined. The changes in the intestinal pathological symptoms and ultrastructure of intestinal, reactive oxygen species (ROS) levels, and antioxidant enzymes were then determined after co-treatment with peptides and TNBS. Transcriptome analysis was used to investigate the underlying ameliorating TNBS-induced colitis effects molecular mechanisms of better activity peptide. Furthermore, quantitative reverse-transcription polymerase chain reaction and molecular docking techniques verified the mRNA sequencing results. Three peptides, MHLWAAK, MAQAAEYYR and MDYYFEER, which significantly inhibit macrophage migration, were synthesized. The results showed that these peptides could effectively alleviate the inflammatory responses in the TNBS-induced zebrafish model of colitis. In addition, co-treatment with TNBS and C-PC peptides could decrease ROS production and increase antioxidant enzyme activities in zebrafish larvae. Moreover, MHLWAAK had the most significantly therapeutic effects on colitis in zebrafish. The transcriptome analysis suggests that the effect of MHLWAAK on TNBS-induced colitis may be associated with the modulation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and mitogen-activated protein kinase (MAPK) signaling pathway associated genes. In addition, molecular docking was conducted to study the prospective interaction between peptides and the key proteins that streamline the Nrf2 and MAPK signaling pathways. IL-6, JNK3, TNF-α, KEAP1-NRF2 complex and MAPK may be the core targets of MHLWAAK in treating colitis. The results suggested that the three C-PC-derived peptides could ameliorate TNBS-induced colitis in zebrafish, and these peptides might be a promising therapeutic candidate for UC treatment.