The effect of alginate oligosaccharides on intestine barrier function and Vibrio parahaemolyticus infections in the white shrimp Litopenaeus vannamei.

The intestine is a host-pathogen interaction site and improved intestinal barrier function help to prevent disease in shrimp. Alginate oligosaccharides (AOS) are derived from resourceful brown algae. The intestine protection properties of AOS were widely recognized, and their benefits in fish have been reported. Nevertheless, there are no reports on AOS in shrimp and other crustaceans. In the present work, we measured the effects of AOS on growth performance and disease resistance in the white shrimp Litopenaeus vannamei and investigated their effects on intestinal health. Shrimps with an initial weight of about 2 g were fed with diets supplemented with 0 (control), 0.07%, 0.2%, 0.6%, or 1.2% of AOS for 56 days and were sampled and challenged with Vibrio parahaemolyticus. Dietary AOS did not significantly influence weight gain or feed utilization (P > 0.05). However, AOS considerably decreased the seven-day cumulative mortality after the challenge at any dose (P < 0.05). Dietary AOS improved the intestinal structure, significantly boosted the intestinal villus height at 0.6% and 1.2% levels, and increased intestinal wall thickness by 0.2%, 0.6%, and 1.2%. The alkaline phosphatase and maltase activities were also increased, suggesting that AOS improved the intestinal condition. Redox homeostasis in intestinal was improved by AOS, as expressed by the enhanced total antioxidant capacity and decreased malonaldehyde content, partly due to the increased superoxide dismutase and catalase activities. Compared with the antioxidant system, AOS's stimulating effects on immunity were more significant. At any level, AOS significantly activated lysozyme activity, the expression of propo and two antimicrobial peptide genes (pen-3 and crusin). However, the lowest concentration of AOS did not stimulate the gene expression of all three assayed pattern recognition receptors (LGBP, Toll, and IMD), and only the highest concentration of AOS increased the expression of imd. These findings suggest that AOS are highly efficient immunostimulants, and various immune pathways in shrimp are differentially sensitive to AOS. Finally, our findings suggest that AOS significantly alter the gut microbiota and their relative abundance at the phylum, family, and genus levels. In conclusion, AOS significantly enhances disease resistance in L. vannamei, possibly attributed to improved intestinal development, increased intestinal immunity and altered microbiota. These findings could provide a basis for future studies on the practical use of AOS and its mechanisms of action.

Preparation and Properties of Salecan-Soy Protein Isolate Composite Hydrogel Induced by Thermal Treatment and Transglutaminase.

Salecan (Sal) is a novel marine microbial polysaccharide. In the present research, Sal and soy protein isolate (SPI) were adopted to fabricate Sal-SPI composite hydrogel based on a stepwise process (thermal treatment and transglutaminase induction). The effect of Sal concentration on morphology, texture properties, and the microstructure of the hydrogel was evaluated. As Sal concentration varied from 0.4 to 0.6 wt%, hydrogel elasticity increased from 0.49 to 0.85 mm. Furthermore, the internal network structure of Sal-SPI composite hydrogel also became denser and more uniform as Sal concentration increased. Rheological studies showed that Sal-SPI elastic hydrogel formed under the gelation process. Additionally, FTIR and XRD results demonstrated that hydrogen bonds formed between Sal and SPI molecules, inferring the formation of the interpenetrating network structure. This research supplied a green and simple method to fabricate Sal-SPI double network hydrogels.

Protective effects of glutamine against soy saponins-induced enteritis, tight junction disruption, oxidative damage and autophagy in the intestine of Scophthalmus maximus L.

Soy saponins, as thermo-stable anti-nutrients in soybean meal (SBM), are the primary causal agents of SBM-induced enteritis, which represents a well-documented pathologic alternation involving the distal intestines of various farmed fish. Our previous work showed that soy saponins might lead to SBM-induced enteritis, destroy tight junction structure and induce oxidative damage in juvenile turbot. Glutamine, as a conditionally essential amino acid, is an important substrate utilized for the growth of intestinal epithelial cells. An 8-week feeding trial was carried out to determine whether glutamine can attenuate the detrimental effects of soy saponins. Three isonitrogenous-isolipidic experimental diets were formulated as follows: (i) fish meal-based diet (FM), considered as control; (ii) FM + 10 g/kg soy saponins, SAP; and (iii) SAP + 15 g/kg glutamine, GLN. The results showed that dietary soy saponins significantly increased the gene expression levels of inflammatory markers (IL-1ß, IL-8 and TNF-α) and related signaling factors (NF-кB, AP-1, p38, JNK and ERK), which were remarkably attenuated by dietary glutamine. Compared to SAP group, GLN-fed fish exhibited significantly higher expression levels of tight junction genes (CLDN3, CLDN4, OCLN, Tricellulin and ZO-1). Glutamine supplementation in SAP diet markedly suppressed the production of reactive oxygen species, malondialdehyde and protein carbonyl, and enhanced the activities of antioxidant enzymes as well as the mRNA levels of HO-1, SOD, GPX and Nrf2. Furthermore, GLN-fed fish had a remarkably lower number of autophagosomes compared to SAP-fed fish. In conclusion, our study indicated that glutamine could reverse the harmful effects of soy saponins on intestinal inflammation, tight junction disruption and oxidative damage, via attenuation of NF-кB, AP-1 and MAPK pathways and activation of Nrf2 pathway. Glutamine may have the function of controlling autophaghic process within an appropriate level of encountering inflammation.

Chitosan and chitooligosaccharides attenuate soyabean meal-induced intestinal inflammation of turbot (Scophthalmus maximus): possible involvement of NF-кB, activator protein-1 and mitogen-activated protein kinases pathways.

An 8-week feeding experiment was conducted to investigate and confront the putative functions of chitosan (CTS) and chitooligosaccharide (COS) in the growth and homoeostasis of distal intestine in juvenile turbots fed diets containing soyabean meal (SBM). Three isolipidic and isonitrogenous diets were formulated by supplemented basal diet (based on a 400 g/kg SBM) with 7·5 g/kg CTS or with 2·0 g/kg COS. Our results indicated that both CTS and COS supplementation could significantly improve (i) the growth performance and feed efficiency ratio; (ii) antioxidant activity driven by metabolic enzymes (i.e. catalase, glutathione reductase, glutathione peroxidase and superoxide dismutase); (iii) glutathione levels; (iv) acid phosphatase and lysozyme activity and (v) IgM content. As a result, these two particular prebiotics were able to significantly attenuate the histological alterations due to local inflammation as well as to decrease the transcriptional levels of proinflammatory cytokines (i.e. IL-1ß, IL-8 and TNF-α) and major pathway effectors (i.e. activator protein-1 (AP-1), NF-кB, p38 mitogen-activated protein kinase, c-Jun N-terminal kinase and extracellular regulated kinase). High-throughput sequencing data indicated that dietary CTS and COS could significantly decrease the diversity of intestinal bacteria but elevate the relative abundances of Bacillus, Lactobacillus and Pseudomonas genera. Altogether, these findings suggest that CTS and COS can improve growth of turbot, enhance intestinal immune and anti-oxidant systems and promote the balance of intestinal microbiota. The protective effects, elicited by these two prebiotics, against SBM-induced inflammation could be attributed to their roles in alleviating the overexpression of inflammatory cytokines by possibly down-regulating NF-кB, AP-1 and/or mitogen-activated protein kinases pathways.

Corn gluten meal induces enteritis and decreases intestinal immunity and antioxidant capacity in turbot (Scophthalmus maximus) at high supplementation levels.

Corn gluten meal (CGM) is an important alternative protein source in aquafeed production. However, in turbot (Scophthalmus maximus), CGM could not be effectively utilized because of its low digestibility, the reason for which is still unclear. The purpose of the present study was to investigate and elucidate the cause for the poor utilization of CGM by turbot from the view of gut health. An 8-week feeding trial was conducted with turbot individuals (initial body weight 11.4 ± 0.2 g), which were fed with one of four isonitrogenous and isolipidic diets formulated to include 0%, 21.2%, 31.8%, and 42.6% CGM to progressively replace 0%, 33%, 50%, and 67% fish meal (FM) protein in a FM-based diet, respectively. The results showed that CGM caused dose-dependent decreases in (1) growth performance, nutrient digestibility, and feed utilization; (2) activities of brush-border membrane enzymes; (3) intestinal antioxidant indices of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase activities, and reduced glutathione level; (4) intestinal immune parameters of acid phosphatase activity, complement 3, complement 4, and IgM concentrations. Dose-dependent increases in the severity of the inflammation, with concomitant alterations on microvilli structure and increasing expression of inflammatory cytokine genes of Il-1ß, Il-8, and Tnf-α were observed but without a change in the intracellular junctions and the epithelial permeability established by the plasma diamine oxidase activity and D-lactate level examinations. In conclusion, the present work proved that CGM negatively affected the gut health of turbot by inducing enteritis and by decreasing intestinal immunity and antioxidant capacity, which could be one of the reasons for the reduced utilization of CGM by turbot.