Effects of Apple Polyphenols and Taurine on Growth Performance, Tissue Morphology, and Lipid and Glucose Metabolism in Rice Field Eel (Monopterus albus) Fed High Oxidized Fish Oil.

The aim of this trial was to investigate the effects of apple polyphenols (AP) and taurine (TA) on the growth performance, tissue morphology, and lipid and glucose metabolism in rice field eel fed diets with high oxidized fish oil (OFO). A 10-week feeding experiment was conducted using juveniles (initial body weight 16.66 ± 0.02 g) fed five different diets. Three diets were formulated with various levels of OFO at 9.5, 600, and 800 meq·kg-1 and named as Control, POV600, and POV800 diet, respectively. The other two diets were POV600 and POV800 supplemented with 0.5% AP and 0.2% TA, respectively. Compared to the Control group, only the eels fed POV800 exhibited an increase in weight gain and specific growth rate along with a reduction in feed conversion ratio. AP and TA did not affect growth performance; juveniles fed AP, however, showed a decrease in liver weight. Both POV600 and POV800 decreased nuclei number and increased vacuoles size in the liver. POV800 damaged the intestinal structure integrity and reduced goblet cells number. AP repaired the liver damage on nuclei number and vacuoles size in fish fed with POV600 diet, while TA mitigated intestinal histopathological damage on intact structure and goblet cells number. The mRNA expression level of liver ampkα in fish fed AP was upregulated, while dietary TA upregulated the mRNA expression levels of liver ampkα and accα. In the muscle, POV600 downregulated mRNA expression levels of accα, cpt1, and lipin, whereas POV800 upregulated mRNA expression levels of accα, pparα, and lipin. Dietary AP and TA could counteract the effects of POV600 and POV800 diet on muscle lipid metabolism. Both POV600 and POV800 diets upregulated mRNA expression levels of liver pck1 and gsk3α. AP and TA both downregulated mRNA expression level of liver pck1, while only TA downregulated the expression of liver gsk3α. AP increased the mRNA expression level of gsk3α in muscle. In summary, inclusion of AP and TA did not affect growth performance but showed a potential to alleviate liver or intestinal damages induced by a high OFO diet. Dietary AP and TA were also found to regulate mRNA expression of genes related to lipid and glucose metabolism.

Integrated transcriptome and metabolome analysis reveals a possible mechanism for the regulation of lipid metabolism via vitamin A in rice field eel (Monopterus albus).

To understand the effects of vitamin A on lipid deposition in rice field eels, integrated liver transcriptome and metabolome were conducted and the changes in the genes and metabolites were assessed. Three groups of rice field eel were fed with 0, 200, and 16,000 IU/kg vitamin A supplementations in their diets for 70 days. The total lipid content in the whole body of the rice field eels was significantly increased with the vitamin A supplementations (p < 0.05). Comparative transcriptome analysis revealed 14 pathways and 46 differentially expressed genes involved in lipid metabolism. Sphingolipid metabolism, glycerolipid metabolism, primary bile acid biosynthesis and steroid hormone biosynthesis were significantly enriched pathways. In these pathways, three differential genes phospholipid phosphatase 1a (PLPP1a), phospholipid phosphatase 2b (PLPP2b), cytochrome P450 21a2 (CYP21a2) were consistent with the change trend of lipid content, and the other three differential genes aldo-keto reductase family 1 member D1 (AKR1D1), uridine diphosphate glucuronic acid transferase 1a1 (UGT1a1), cytochrome P450 1a (CYP1a) were opposite. Metabolomic analysis revealed that primary bile acid biosynthesis, sphingolipid metabolism, steroid hormone biosynthesis and biosynthesis of unsaturated fatty acids were all critical for rice field eel metabolic changes in response to vitamin A. Six important differential metabolites (eicosapentaenoic acid, sphinganine, 11-beta-hydroxyprogesterone, hydroxyeicosatetraenoic acid, cholic acid, and glycochenodeoxycholate) were identified and have provided new insights into how vitamin A regulates lipid deposition. Integrated transcriptome and metabolome analyses revealed that primary bile acid biosynthesis was the only remarkably enriched pathway in both the transcriptome and metabolome while that sphingosine was the main metabolite. Based on the above results, we have concluded that vitamin A promotes lipid deposition in the rice field eel through the primary bile acid synthesis pathway, and lipid deposits are widely stored in cell membranes, mainly in the form of sphingosine. These results will provide reference data to help improve our understanding of how vitamin A regulates lipid metabolism.

Dietary supplementation of ß-1, 3-glucan improves the intestinal health of white shrimp (Litopenaeus vannamei) by modulating intestinal microbiota and inhibiting inflammatory response.

The phenomenon of intestinal dysfunction is widely observed in white shrimp (Litopenaeus vannamei) culture, and ß-1,3-glucan has been confirmed to be beneficial in intestinal health with a lack understanding of its underlying mechanism. Proteobacteria, Firmicutes, and Actinobacteria served as the predominant phyla inhabiting the intestine of white shrimp, whilst a significant variation in their proportion was recorded in shrimp fed with basal and ß-1,3-glucan supplementation diets in this study. Dietary supplementation of ß-1,3-glucan could dramatically increase the microbial diversity and affect microbial composition, concurrent with a notable reduction in the ratio of opportunistic pathogen Aeromonas, gram-negative microbes, from Gammaproteobacteria compared to the basal diet group. The benefits for microbial diversity and composition by ß-1,3-glucan improved the homeostasis of intestinal microbiota through the increase of specialists' number and inhibition of microbial competition caused by Aeromonas in ecological networks; afterward, the inhibition of Aeromonas by ß-1,3-glucan diet dramatically suppressed microbial metabolism related to lipopolysaccharide biosynthesis, followed by a conspicuous decrease in the intestinal inflammatory response. The improvement of intestinal health referred to the elevation in intestinal immune and antioxidant capacity, ultimately contributing to the growth of shrimp fed ß-1,3-glucan. These results suggested that ß-1,3-glucan supplementation improved the intestinal health of white shrimp through the modulation of intestinal microbiota homeostasis, the suppression of intestinal inflammatory response, and the elevation of immune and antioxidant capacity, and subsequently promoted the growth of white shrimp.

Dietary Macroalgae Saccharina japonica Ameliorates Liver Injury Induced by a High-Carbohydrate Diet in Swamp Eel (Monopterus albus).

A high-carbohydrate diet lowers the rearing cost and decreases the ammonia emission into the environment, whereas it can induce liver injury, which can reduce harvest yields and generate economic losses in reared fish species. Macroalgae Saccharina japonica (SJ) has been reported to improve anti-diabetic, but the protective mechanism of dietary SJ against liver injury in fish fed a high-carbohydrate diet has not been studied. Therefore, a 56-day nutritional trial was designed for swamp eel Monopterus albus, which was fed with the normal diet [20% carbohydrate, normal carbohydrate (NC)], a high carbohydrate diet (32% carbohydrate, HC), and a HC diet supplemented with 2.5% SJ (HC-S). The HC diet promoted growth and lowered feed coefficient (FC), whereas it increased hepatosomatic index (HSI) when compared with the NC diet in this study. However, SJ supplementation increased iodine contents in muscle, reduced HSI, and improved liver injury, such as the decrease of glucose (GLU), total bile acid (TBA), and alanine aminotransferase (ALT) in serum, and glycogen and TBA in the liver. Consistently, histological analysis showed that SJ reduced the area of lipid droplet, glycogen, and collagen fiber in the liver (p < 0.05). Thoroughly, the underlying protective mechanisms of SJ supplementation against HC-induced liver injury were studied by liver transcriptome sequencing coupled with pathway analysis. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the differentially expressed genes (DEGs), such as the acetyl-coenzyme A synthetase (acss1), alcohol dehydrogenase (adh), interferon-induced protein with tetratricopeptide repeats 1 (ifit1), aldo-keto reductase family 1 member D1 (akr1d1), cholesterol 7-alpha-monooxygenase (cyp7a1), and UDP-glucuronosyltransferase (ugt), indicated that the pathway of glycolysis/gluconeogenesis was the main metabolic pathway altered in the HC group compared with the NC group. Meanwhile, hepatitis C, primary BA biosynthesis, and drug metabolism-cytochrome P450 were the three main metabolic pathways altered by SJ supplementation when compared with the HC group. Moreover, the BA-targeted metabolomic analysis of the serum BA found that SJ supplementation decreased the contents of taurohyocholic acid (THCA), taurochenodeoxycholic acid (TCDCA), taurolithocholic acid (TLCA), nordeoxycholic acid (NorDCA), and increased the contents of ursocholic acid (UCA), allocholic acid (ACA), and chenodeoxycholic acid (CDCA). In particular, the higher contents of UCA, ACA, and CDCA regulated by SJ were associated with lower liver injury. Overall, these results indicate that the 2.5% supplementation of SJ can be recommended as a functional feed additive for the alleviation of liver injury in swamp eel-fed high-carbohydrate diets.

Molecular ecological network analysis reveals the effects of probiotics and florfenicol on intestinal microbiota homeostasis: An example of sea cucumber.

Animal gut harbors diverse microbes that play crucial roles in the nutrition uptake, metabolism, and the regulation of host immune responses. The intestinal microbiota homeostasis is critical for health but poorly understood. Probiotics Paracoccus marcusii DB11 and Bacillus cereus G19, and antibiotics florfenicol did not significantly impact species richness and the diversity of intestinal microbiota of sea cucumber, in comparison with those in the control group by high-throughput sequencing. Molecular ecological network analysis indicated that P. marcusii DB11 supplementation may lead to sub-module integration and the formation of a large, new sub-module, and enhance species-species interactions and connecter and module hub numbers. B. cereus G19 supplementation decreased sub-module numbers, and increased the number of species-species interactions and module hubs. Sea cucumber treated with florfenicol were shown to have only one connecter and the lowest number of operational taxonomic units (OTUs) and species-species interactions within the ecological network. These results suggested that P. marcusii DB11 or B. cereus G19 may promote intestinal microbiota homeostasis by improving modularity, enhancing species-species interactions and increasing the number of connecters and/or module hubs within the network. In contrast, the use of florfenicol can lead to homeostatic collapse through the deterioration of the ecological network.

Effects of dietary Bacillus cereus G19, B. cereus BC-01, and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression of immune-related genes in coelomocytes and intestine of the sea cucumber (Apostichopus japonicus Selenka).

Probiotics have positive effects on the nutrient digestibility and absorption, immune responses, and growth of aquatic animals, including the sea cucumber (Apostichopus japonicus Selenka). A 60-day feeding trial was conducted to evaluate the effects of Bacillus cereus G19, B. cereus BC-01 and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression level of four immune-related genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) in coelomocytes and the intestine of juvenile sea cucumbers. One group was fed the basal diet (control group), while three other groups were fed the basal diet supplemented with B. cereus G19 (G19 group), B. cereus BC-01 (BC group), or P. marcusii DB11 (PM group). The growth rate of sea cucumbers fed diets with probiotics supplementation was significantly higher than that of the control group (P < 0.05). Sea cucumbers in the G19 and PM groups had a significantly greater phagocytic activity of coelomocytes compared to the control group (P < 0.05), while those in the G19 and BC groups had a greater respiratory burst activity (P < 0.05). The alkaline phosphatase (AKP) activity of coelomocytes in sea cucumbers fed diets with probiotics supplementation was significantly higher than the control group (P < 0.05). Comparatively, superoxide dismutase (SOD) activity of coelomocytes for sea cucumber in the PM group was significantly greater (P < 0.05). As for the immune-related genes, B. cereus G19 supplementation significantly increased the expression level of the Aj-rel gene in coelomocytes (P < 0.05), while B. cereus BC-01 supplementation significantly increased that of the Aj-p50 gene as compared to the control group (P < 0.05). In the intestine, the relative expression level of Aj-p105, Aj-p50, and Aj-lys genes in the PM group was significantly higher than that in the control group (P < 0.05). These results suggested that B. cereus G19 and B. cereus BC-01 supplementation could improve the growth performance and the immune response in coelomocytes, while P. marcusii DB11 supplementation could have a positive effect on the growth performance and immune response in coelomocytes and the intestine of sea cucumbers.

Intestinal microbiota and immune related genes in sea cucumber (Apostichopus japonicus) response to dietary ß-glucan supplementation.

ß-glucan is a prebiotic well known for its beneficial outcomes on sea cucumber health through modifying the host intestinal microbiota. High-throughput sequencing techniques provide an opportunity for the identification and characterization of microbes. In this study, we investigated the intestinal microbial community composition, interaction among species, and intestinal immune genes in sea cucumber fed with diet supplemented with or without ß-glucan supplementation. The results show that the intestinal dominant classes in the control group are Flavobacteriia, Gammaproteobacteria, and Alphaproteobacteria, whereas Alphaproteobacteria, Flavobacteriia, and Verrucomicrobiae are enriched in the ß-glucan group. Dietary ß-glucan supplementation promoted the proliferation of the family Rhodobacteraceae of the Alphaproteobacteria class and the family Verrucomicrobiaceae of the Verrucomicrobiae class and reduced the relative abundance of the family Flavobacteriaceae of Flavobacteria class. The ecological network analysis suggests that dietary ß-glucan supplementation can alter the network interactions among different microbial functional groups by changing the microbial community composition and topological roles of the OTUs in the ecological network. Dietary ß-glucan supplementation has a positive impact on immune responses of the intestine of sea cucumber by activating NF-κB signaling pathway, probably through modulating the balance of intestinal microbiota.