Impaired intestinal physical barrier of on-growing grass carp by deficient iron under Aeromonas hydrophila infection

Abstract

This research discovered the impacts of dietary iron on intestine health of on-growing grass carp (Ctenopharyngodon idella). Six hundred and thirty grass carp (242.32 ± 0.58 g) were fed different diets containing 12.15, 35.38, 63.47, 86.43, 111.09, 136.37 and 73.50 mg iron/kg, where the iron source first six groups was ferrous fumarate, and the last group was ferrous sulfate. Feeding trial lasted for sixty days. Thereafter, a fourteen days' challenge test was carried out through Aeromonas hydrophila infection. Previous study showed that the optimum iron level of on-growing grass carp based on per weight gain was estimated to be 75.65 mg/kg. Results from the present study displayed that in contrast to optimum iron level, deficient iron downregulated gene expression of tight junction complexes, Apoptosis regulator Bcl-2 (Bcl-2), MCL1 apoptosis regulator BCL2 family member (Mcl-1), inhibitor of apoptosis protein (IAP) and NF-E2-related factor 2 (Nrf2). It also reduced activities and gene expression of antioxidant enzymes, and upregulated gene expression of apoptosis-related cysteine peptidase CASP (caspase) -2, -7, -8, -9, apoptotic protease activating factor 1 (Apaf-1), Apoptosis regulator Bax (Bax) (in MI and DI), Fas ligand (FasL), p38 mitogen activated protein kinase (p38MAPK), Kelch like ECH associated protein 1a (Keap1a), Keap1b, claudin-12 and myosin light chain kinase (MLCK). In addition, deficient iron raised malondialdehyde (MDA), protein carbonyl (PC) and reactive oxygen species (ROS) generation in intestine of grass carp (P < 0.05). These data demonstrated that deficient iron is harmful to intestinal physical barrier of fish. Besides, the efficiency of ferrous fumarate on intestinal physical barrier function was better than ferrous sulfate in fish. At last, based on MDA contents in MI and DI, the iron requirements were 83.40 and 80.20 mg/kg diet (ferrous fumarate as sources), respectively.