Isalo scorpion Cytotoxic peptide (IsCT) improved the physical barrier of the intestine on on-growing grass carp (Ctenopharyngodon idella)

Isalo scorpion cytotoxic peptide (IsCT) is an a-helical antimicrobial peptide with antibacterial and immunomodulatory activities. This research was performed to examine the link between Isalo scorpion cytotoxic peptide (IsCT) and the physical barrier of the intestine partially linked to antioxidant activity, apoptosis, and apical junction complex (AJC) of grass carp. Within sixty days, fish were arbitrarily divided into six treatments and fed six levels of IsCT (0, 0.6, 1.2, 1.8, 2.4, and 3.0 mg/kg diet), respectively. A six-day challenge test of Aeromonas hydrophila was subsequently performed. We found that appropriate IsCT supplementation (1.8 mg/kg diet) (1) reduced reactive oxygen species (ROS), protein carbonyl (PC) and malondialdehyde (MDA) contents, increased antioxidant enzyme activities and mRNA levels partly linked to regulation of the Kelch-like-ECH-associated protein (Keap)/NF-E2-related factor 2 (Nrf2) signaling in the intestines; (2) decreased DNA fragmentation and alleviated apoptosis partially associated with the intrinsic pathway [(Bcl-2, Mcl-1, and Bax)/Apaf-1/caspase-9/ caspase-3] and the extrinsic pathway (FasL/caspase-8/caspase-3, -7) regulated by the c-Jun N-terminal kinase (JNK) [not p38 mitogen-activated protein kinase (p38 MAPK)] signaling pathway in fish intestines; (3) ameliorated intestinal AJC barrier partially linked to strengthening the tight junction (TJ) and adherents junction (AJ) integrity regulated by a small Rho GTPase protein (RhoA)/the Rho-associated protein kinase (ROCK) signaling pathway in fish intestines. However, the mRNA expression of glutathione-S-transferase P2 (GSTP2), p38 MAPK, claudin-7a, claudin-7b, and claudin-15b in the intestines of grass carp was unaffected by IsCT supplementation. Our research revealed that IsCT enhanced the physical barrier of fish intestines associated with maintaining intestinal epithelial cells (IECs) and apical junctional complex (AJC) integrity. Based on ROS and PC contents, the appropriate levels of IsCT in grass carp were determined to be 1.78 and 1.77 mg/kg diet, respectively.