Effects of tributyrin and alanyl-glutamine dipeptide on intestinal health of largemouth bass (Micropterus salmoides) fed with high soybean meal diet

A Comparative Study on Effects of Three Butyric Acid-Producing Additives on the Growth Performance, Non-specific Immunity, and Intestinal Microbiota of the Sea Cucumber Apostichopus japonicus

The providers of butyric acid, Clostridium butyricum (CB), sodium butyrate (SB), and tributyrin (TB), have been extensively studied as aquafeed additives in recent years. However, no comparative study has been reported on the probiotic effects of CB, SB, and TB as feed additives on sea cucumber (Apostichopus japonicus). A 63-day feeding trial was performed to assess the effects of dietary live cells of C. butyricum (CB group, the basal diet supplemented with 1% CB), sodium butyrate (SB group, the basal diet supplemented with 1% SB), and tributyrin (TB group, the basal diet supplemented with 1% TB) on the growth, non-specific immunity, and intestinal microbiota of A. japonicus with a basal diet group as the control. Results indicated that all three additives considerably increased A. japonicus growth, with dietary CB having the optimal growth-promoting effect. Of the seven non-specific enzyme parameters measured in coelomocytes of A. japonicus (i.e., the activities of phagocytosis, respiratory burst, superoxide dismutase, alkaline phosphatase, acid phosphatase, catalase, and lysozyme), dietary CB, SB, and TB considerably increased the activities of six, five, and six of them, respectively. The immune genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) expression in the mid-intestine tissues of A. japonicus was significantly increased by all three additives. The CB group had the highest expression of all four genes. Additionally, the relative expression of Aj-p105, Aj-p50, and Aj-lys genes was significantly up-regulated in the three additive groups after stimulation with inactivated Vibrio splendidus. Dietary CB enhanced the intestinal microbial diversity and richness in A. japonicus while dietary TB decreased them. Meanwhile, dietary CB, SB, and TB significantly enhanced the abundance of Firmicutes, unclassified_f_Rhodobacteraceae, and Proteobacteria, respectively, while dietary CB and SB reduced the abundance of Vibrio. Dietary CB and SB improved the stability of microbial ecosystem in the intestine of A. japonicus. In contrast, dietary TB appeared to have a negative effect on the stability of intestinal microbial ecosystem. All three additives improved the intestinal microbial functions associated with energy production and immunity regulation pathways, which may contribute directly to growth promotion and non-specific immunity enhancement in A. japonicus. Collectively, in terms of enhancing growth and non-specific immunity, as well as improving intestinal microbiota, dietary live cells of C. butyricum exhibited the most effective effects in A. japonicus.

Glycerol tributylate (Triacylglycerol tributanoate) promoted the liver lipid metabolism by cultivating the intestinal flora of grass carp (Ctenopharyngodon idellus)

To investigate the effects of glycerol tributyrin (TB) (Triacylglycerol tributanoate) on the regulation of liver lipid metabolism by intestinal flora of grass carp (Ctenopharyngodon idellus). The compound feed with soybean oil 2.8% + fish oil 1.8%, soybean oil 6.3% + fish oil 1.8%, and soybean oil 6.2% + fish oil 1.8% + TB 0.1% was added to the basal diet as a fat source and fed to the basal (control) group, high lipid (HL) group, and tributyrin (TB) group for 12 weeks. We tested the growth performance, fat content, diversity, and abundance of gut flora and other related indexes of grass carp by Soxhlet extraction, liver tissue enzyme activity, oil red O staining, and 16S rRNA high-throughput sequencing. The results showed that the liver fat number and liver fat content of grass carp in the TB group were lower than those in the HL group, while the fattening degree was significantly higher than those in the other two groups; according to the indices such as Shannon, Ace, and Coverage, it was found that the grass carp in the TB group had the highest abundance and diversity of intestinal microflora; at the portal level, Proteobacteria and Fusobacteria were the main dominant flora in the TB group, with the number of unique OUTs accounting for about 59. 9% of the total number measured; at the genus level, the relative abundance of lipase-producing, short-chain fatty acid-associated bacteria, such as Bacillus-Lactobacillus and Bifidobacterium, was significantly lower (p < 0.05). Thus, we conclude that the addition of TB to high-fat diets can alter the structure of the intestinal microbial community and promote hepatic lipid metabolism in grass carp. TB can alleviate fatty liver in grass carp by increasing the relative abundance of short-chain fatty acids in the intestine. Meanwhile, TB inhibits the conversion of primary bile acids to secondary bile acids in the host, which can block intestinal FXR signaling and the hepatic FXR-SHP pathway, thus slowing down fat synthesis and alleviating the accumulation of liver lipids in grass carp.

Comparative Transcriptomic Analysis of Largemouth Bass (Micropterus salmoides) Livers Reveals Response Mechanisms to High Temperatures

High temperatures are considered one of the most significant limitations to subtropical fishery production. Largemouth bass (Micropterus salmoides) is an economically important freshwater species grown in subtropical areas, which are extremely sensitive to heat stress (HS). However, comprehensive transcriptomic data for the livers of largemouth bass in response to HS are still lacking. In this study, a comparative transcriptomic analysis was performed to investigate the gene expression profiles of the livers of largemouth bass under HS treatment. As a result, 6114 significantly differentially expressed genes (DEGs), which included 2645 up-regulated and 3469 down-regulated genes, were identified in response to HS. Bioinformatics analyses demonstrated that the 'ECM-receptor interaction' pathway was one of the most dramatically changed pathways in response to HS, and eight DEGs assigned to this pathway were taken as hub genes. Furthermore, the expression of these eight hub genes was determined by quantitative reverse transcription PCR, and all of them showed a significant change at the transcriptional level, suggesting a crucial role of the 'ECM-receptor interaction' pathway in the response of largemouth bass to HS. These findings may improve our understanding of the molecular mechanisms underlying the response of largemouth bass to HS.

Alpha-ketoglutaric acid mitigates the detrimental effects of soy antigenic protein on the intestinal health and growth performance of Mirror carp Cyprinus carpio

The study investigated the alleviated effects of Alpha-ketoglutaric acid (AKG) on the intestinal health of mirror carp (Cyprinus carpio Songpu) caused by soy antigenic protein. The diets were formulated from fishmeal (CON), 50% soybean meal (SBM), the mixture of glycinin and β-conglycinin (11 + 7S) and adding 1% AKG in the 11 + 7S (AKG). Carp (~ 4 g) in triplicate (30 fish per tank) was fed to apparent satiation thrice a day for six weeks. Compared with CON, SBM treatment resulted in significantly poor growth performance (P < 0.05), whereas 11 + 7S and AKG treatments were not significantly different from CON (P > 0.05). Gene expression of tumor necrosis factor (TNF-α) and interleukin-1 β (IL-1β) in proximal intestines (PI) and distal intestines (DI) were increased (P < 0.05), and transforming growth factor (TGF-β) in PI and middle intestines (MI) was decreased (P < 0.05) in both SBM and 11 + 7S. The caspase-3 in DI increased in SBM (P < 0.05) and the caspase-3 and caspase-9 in DI increased in 11 + 7S (P < 0.05); conversely, TGF-β in PI and MI was increased, TNF-α and IL-1β in the MI, caspase-3, and caspase-9 in DI was decreased in AKG (P < 0.05). The TOR (target of rapamycin) in PI and MI, ACC in PI, MI and DI was decreased in SBM (P < 0.05), the AMPK in the PI and DI, TOR in PI, MI and DI, ACC in PI and DI, 4E-BP in DI was reduced in 11 + 7S (P < 0.05). AMPK in the PI and DI, ACC in the PI and MI, TOR in PI, MI, and DI, 4E-BP in PI and DI was recovered by AKG supplementation (P < 0.05). Lipids and lipid-like metabolism, organic acids and derivatives metabolism increased in AKG dietary treatment. In conclusion, AKG reduces the expression of intestinal inflammation and apoptosis pathway and changes glycerophospholipid metabolism and sphingolipid metabolism in the intestine of fish.