Abstract
This experiment was performed to investigate the effects of soybean meal on intestinal health of Songpu Mirror carp (Cyprinus carpio Songpu) as well as the mechanism of AKG alleviating intestinal injury. A total of 609 juvenile Songpu mirror carp with an initial body weight of (9.51±0.06) g were randomly divided into 7 groups with 3 replicates per group and 29 fish per group. The control group was fed with 30.8 % fish meal (FM group) as the protein source. The experimental group was fed with 40 % soybean meal (SM group) as basic diet. The AKG group were fed with the basic diet supplemented with 1% α-ketoglutarate. Groups Met and Com were fed with the basic diet supplemented with 300 mg/kg Metformin and 0.2 mg/kg Compound C respectively. Groups Met+AKG and Com+AKG were supplemented with Metformin and Compound C on the basis of AKG group respectively. The experiment lasted for 59 days. Compared with FM group, mucosa ATP and ADP contents of the distal intestine (DI) were significantly increased (P<0.05) in SM group. Meanwhile, the expression of ACC, tumor necrosis factor alfa (TNF-α), interleukin-1 beta (IL-1β), transforming growth factor-beta (TGFβ2), caspase9, Claudin7, Claudin11, Claudin3c, Occludin in the proximal intestine (PI), the expression of AMP-activated protein kinase alfa (AMPK-α), target of rapamycin (TOR), ACC, IL-1β, TGFβ1, Caspase8, Claudin7, Occludin in the mid intestine (MI), the expression of TGFβ1, caspase8, caspase9 in the DI were significantly decreased and the expression of TNF-a, Claudin11, Claudin3c, Occludin in the DI were significantly increased (P<0.05) in SM. Compared with SM, the expression of TGFβ1 (PI), Claudin7 (PI), Claudin11 (PI, MI and DI), TOR (PI and MI), caspase8(MI), TNF-α (MI) and Occludin (DI) were significantly decreased (P<0.05) in AKG group. The ADP and AMP contents of mucosa of DI were significantly increased in Met and Com group. Subsequently, the expression of AMPK-α (PI), TOR (MI and DI), TNF-α (PI), IL-1β (PI), Caspase9 (PI), Claudin7 (PI), Claudin11 (PI and MI), Claudin3c (PI), TGFβ1 (MI) were significantly increased and the expression of Occludin were significantly decreased in Met group. The expression of Occludin (PI) were significantly increased and the expression of Claudin11(MI and DI) and Occludin (DI) were significantly decreased in Com group. Compared with AKG, the ATP, ADP and AMP contents of mucosa of DI were significantly increased in Com+AKG group. The ADP contents of mucosa of DI were significantly increased in Met+AKG group. The expression of Claudin7 (PI), Claudin11(PI) and TOR (MI) were significantly decreased in Met+AKG and Com+AKG. Morever, the expression of caspase8 (PI), Claudin11 (MI) and Claudin7(DI) were significantly increased in Met+AKG. The expression of Claudin11 (DI) and Occludin (DI) were significantly increased in Com+AKG (P<0.05). In conclusion, soybean meal decreased the energy level of PI and MI, but inhibited the expression of AMPK-α, TOR and ACC, and further decreased the expression of tight junction protein in PI and MI. Intestinal inflammation in DI was triggered. AKG can improve the expression of TOR, tight junction and anti-inflammatory factors in PI, reduce the expression of pro-inflammatory factors in MI and DI, alleviate the apoptosis of MI and DI by inhibiting endogenous apoptosis, and alleviate the damage of soybean meal to the intestine of carp. This study found the way that soy protein would damage intestinal health, and its effect on intestinal mucosal energy metabolism and the mechanism of AKG in alleviating intestinal injury. So this may provide a theoretical basis for improving the application of soybean in aquatic animal production.
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