Abstract
As an intermediate substance of the tricarboxylic acid cycle and a precursor substance of glutamic acid synthesis, the effect of alpha-ketoglutarate on growth and protein synthesis has been extensively studied. However, its prevention and treatment of pathogenic bacteria and its mechanism have not yet been noticed. To evaluate the effects of alpha-ketoglutarate on intestinal antioxidant capacity and immune response of Songpu mirror carp, a total of 360 fish with an average initial weight of 6.54 ± 0.08 g were fed diets containing alpha-ketoglutarate with 1% for 8 weeks. At the end of the feeding trial, the fish were challenged with Aeromonas hydrophila for 2 weeks. The results indicated that alpha-ketoglutarate supplementation significantly increased the survival rate of carp after infection with Aeromonas hydrophila (P < 0.05), and the contents of immune digestion enzymes including lysozyme, alkaline phosphatase and the concentration of complement C4 were markedly enhanced after alpha-ketoglutarate supplementation (P < 0.05). Also, appropriate alpha-ketoglutarate increased the activities of total antioxidant capacity and catalase and prevented the up-regulation in the mRNA expression levels of pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, interleukin-6, and interleukin-8 (P < 0.05). Furthermore, the mRNA expression levels of toll-like receptor 4 (TLR4), and nuclear factor kappa-B (NF-κB) were strikingly increased after infection with Aeromonas hydrophila (P < 0.05), while the TLR4 was strikingly decreased with alpha-ketoglutarate supplementation (P < 0.05). Moreover, the mRNA expression levels of tight junctions including claudin-1, claudin-3, claudin-7, claudin-11 and myosin light chain kinases (MLCK) were upregulated after alpha-ketoglutarate supplementation (P < 0.05). In summary, the appropriate alpha-ketoglutarate supplementation could increase survival rate, strengthen the intestinal enzyme immunosuppressive activities, antioxidant capacities and alleviate the intestinal inflammation, thereby promoting the intestinal immune responses and barrier functions of Songpu mirror carp via activating TLR4/MyD88/NF-κB and MLCK signaling pathways after infection with Aeromonas hydrophila.
Highlights
Extensive aquaculture practices subject fish to environmental stress, increasing the susceptibility to various pathogens [1]
The results indicated that the activities of SOD, CAT and total antioxidant capacity (T-AOC) were significantly decreased after infection with A. hydrophila (P < 0.05), and the supplementation of AKG generated a remarkable increase of the activities of CAT and T-AOC (P < 0.05)
A. hydrophila, which is an emergent bacterial pathogen that is commonly encountered in freshwater, was selected as the inflammatory infection model of Songpu mirror carp in this study
Summary
Extensive aquaculture practices subject fish to environmental stress, increasing the susceptibility to various pathogens [1]. Antimicrobial agent or immunotherapeutic agent that can effectively prevent and cure pathogenic bacteria is one of great significance to the healthy growth of aquatic animals and even humans. A handful of studies have been reported the clinical benefits of AKG in improving immunity in malnutrition or inflammatory diseases to maintain intestinal structure and function under stress [12, 13]. These observations indicated that AKG supplementation may has beneficial effects on the intestinal innate immune response of fish, and this possibility is worthy of study with respect to aquatic animals. Our previous studies on Songpu mirror carp have shown that AKG had a beneficial effect on increasing the growth performance and protein efficiency [15, 16], while information regarding the effects of AKG supplementation on innate immune response in Songpu mirror carp is scarce, and little is known about the molecular mechanisms responsible for the action of AKG on the intestine of carp
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