Threonine deficiency decreased intestinal immunity and aggravated inflammation associated with NF-κB and target of rapamycin signalling pathways in juvenile grass carp (Ctenopharyngodon idella) after infection with Aeromonas hydrophila

Exploring the dietary strategies of phenylalanine: Improving muscle nutraceutical quality as well as muscle glycogen and protein deposition in adult grass carp (Ctenopharyngodon idella)

Muscle is the main edible part of bony fish. The purpose of this study was to investigate the influences of phenylalanine (Phe) on muscle quality, amino acid composition, fatty acid composition, glucose metabolism, and protein deposition in adult grass carp. The diets at 2.30, 4.63, 7.51, 10.97, 13.53, and 17.07 g/kg Phe levels were fed for 9 weeks. The results manifested that Phe (10.97-13.53 g/kg) increased the pH of the fillets and decreased muscle cooking loss and lactic acid content; Phe (7.51-17.07 g/kg) improved the composition of the fillets in terms of flavor (free) amino acids, bound amino acids (especially EAA), and fatty acids (especially EPA and DHA); Phe (7.51-13.53 g/kg) increased muscle glycogen content (possibly related to the AMPK signaling pathway) and muscle protein deposition (possibly related to IGF-1/4EBP1/TOR and AKT/FOXOs signaling pathways). In conclusion, a diet with appropriate Phe levels could improve fillet quality.

Unveiling the emerging role of curcumin to alleviate ochratoxin A-induced muscle toxicity in grass carp (Ctenopharyngodon idella): in vitro and in vivo studies

BACKGROUND

Ochratoxin A (OTA), a globally abundant and extremely hazardous pollutant, is a significant source of contamination in aquafeeds and is responsible for severe food pollution. The developmental toxicity of OTA and the potential relieving strategy of natural products remain unclear. This study screened the substance curcumin (Cur), which had the best effect in alleviating OTA inhibition of myoblast proliferation, from 96 natural products and investigated its effect and mechanism in reducing OTA myotoxicity in vivo and in vitro.

METHODS

A total of 720 healthy juvenile grass carp, with an initial average body weight of 11.06 ± 0.05 g, were randomly assigned into 4 groups: the control group (without OTA and Cur), 1.2 mg/kg OTA group, 400 mg/kg Cur group, and 1.2 mg/kg OTA + 400 mg/kg Cur group. Each treatment consisted of 3 replicates (180 fish) for 60 d.

RESULTS

Firstly, we cultured, purified, and identified myoblasts using the tissue block culture method. Through preliminary screening and re-screening of 96 substances, we examined cell proliferation-related indicators such as cell viability and ultimately found that Cur had the best effect. Secondly, Cur could alleviate OTA-inhibited myoblast differentiation and myofibrillar development-related proteins (MyoG and MYHC) in vivo and in vitro and improve the growth performance of grass carp. Then, Cur could also promote the expression of OTA-inhibited protein synthesis-related proteins (S6K1 and TOR), which was related to the activation of the AKT/TOR signaling pathway. Finally, Cur could downregulate the expression of OTA-enhanced protein degradation-related genes (murf1, foxo3a, and ub), which was related to the inhibition of the FoxO3a signaling pathway.

CONCLUSIONS

In summary, our data demonstrated the effectiveness of Cur in alleviating OTA myotoxicity in vivo and in vitro. This study confirms the rapidity, feasibility, and effectiveness of establishing a natural product screening method targeting myoblasts to alleviate fungal toxin toxicity.

Novel Perspective on Mechanism in Muscle Growth Inhibited by Ochratoxin A Associated with Ferroptosis: Model of Juvenile Grass Carp (Ctenopharyngodon idella) In Vivo and In Vitro Trials

Ochratoxin A (OTA) is a common mycotoxin in food and feed that seriously harms human and animal health. This study investigated the effect of OTA on the muscle growth of juvenile grass carp (Ctenopharyngodon idella) and its possible mechanism in vitro. Our results have the following innovative findings: (1) Dietary OTA increased the expression of increasing phase I metabolic enzymes and absorbing transporters while reducing the expression of efflux transporters, thereby increasing their residue in muscles; (2) OTA inhibited the expressions of cell cycle and myogenic regulatory factors (MyoD, MyoG, and MyHC) and induced ferroptosis by decreasing the mRNA and protein expressions of FTH, TFR1, GPX4, and Nrf2 both in vivo and in vitro; and (3) the addition of DFO improved OTA-induced ferroptosis of grass carp primary myoblasts and promoted cell proliferation, while the addition of AKT improved OTA-inhibited myoblast differentiation and fusion, thus inhibiting muscle growth. Overall, this study provides a potential research target to further mitigate the myotoxicity of OTA.

Metabolomics and lipidomics in non-small cell lung cancer

Due to its insidious nature, lung cancer remains a leading cause of cancer-related deaths worldwide. Therefore, there is an urgent need to identify sensitive/specific biomarkers for early diagnosis and monitoring. The current study was designed to provide a current metabolic profile of non-small cell lung cancer (NSCLC) by systematically reviewing and summarizing various metabolomic/ lipidomic studies based on NSCLC blood samples, attempting to find biomarkers in human blood that can predict or diagnose NSCLC, and investigating the involvement of key metabolites in the pathogenesis of NSCLC. We searched all articles on lung cancer published in Elsevier, PubMed, Web of Science and the Cochrane Library between January 2012 and December 2022. After critical selection, a total of 31 studies (including 2768 NSCLC patients and 9873 healthy individuals) met the inclusion criteria, and 22 were classified as "high quality". Forty-six metabolites related to NSCLC were repeatedly identified, involving glucose metabolism, amino acid metabolism, lipid metabolism and nucleotide metabolism. Pyruvic acid, carnitine, phenylalanine, isoleucine, kynurenine and 3-hydroxybutyrate showed upward trends in all studies, citric acid, glycine, threonine, cystine, alanine, histidine, inosine, betaine and arachidic acid showed downward trends in all studies. This review summarizes the existing metabolomic/lipidomic studies related to the identification of blood biomarkers in NSCLC, examines the role of key metabolites in the pathogenesis of NSCLC, and provides an important reference for the clinical diagnosis and treatment of NSCLC. Due to the limited size and design heterogeneity of the existing studies, there is an urgent need for standardization of future studies, while validating existing findings with more studies.

Ammonia-induced oxidative stress triggered apoptosis in the razor clam (Sinonovacula constricta)

As one of the most significant contaminants and stressors in aquaculture systems, ammonia adversely jeopardizes the health of aquatic animals. Ammonia exposure affects the development, metabolism, and survival of shellfish. However, the responses of the innate immune and antioxidant systems and apoptosis in shellfish under ammonia stress have rarely been reported. In this study, razor clams (Sinonovacula constricta) were exposed to different concentrations of non-ion ammonia (0.25 mg/L, 2.5 mg/L) for 72 h and then placed in ammonia-free seawater for 72 h for recovery. The immune responses induced by ammonia stress on razor clams were investigated by antioxidant enzyme activities and degree of apoptosis in digestive gland and gill tissues at different time points. The results showed that exposure to a high concentration of ammonia greatly disrupted the antioxidant system of the razor clam by exacerbating the accumulation of reactive oxygen species ( O 2 - , H2O2) and disordering the activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and the level of activity remained at a significantly high level after recovering for 72 h (P < 0.05). In addition, there were significant differences (P < 0.05) in the expression of key genes (Caspase 7, Cyt-c, Bcl-2, and Bax) in the mitochondrial apoptotic pathway in the digestive glands and gills of razor clams as a result of ammonia stress and were unable to return to normal levels after 72 h of recovery. TUNEL staining indicated that apoptosis was more pronounced in gills, showing a dose and time-dependent pattern. As to the results, ammonia exposure leads to the activation of innate immunity in razor clams, disrupts the antioxidant system, and activates the mitochondrial pathway of apoptosis. This is important for comprehending the mechanism underlying the aquatic toxicity resulting from ammonia in shellfish.

Transcriptional responses of liver and spleen in Lota lota to polyriboinosinic polyribocytidylic acid

Introduction

The cultured Lota lota can meet the market demand in the context of the decline of wild resources, but the disease in the high-density culture process also deserves attention. Therefore, understanding the immune regulation mechanisms of L. lota will be the basis for obtaining high benefits in artificial culture.

Methods

To explore the viral response mechanism of L. lota, RNA-seq was applied to identify the transcriptomic changes of the liver and spleen in L. lota by poly (I:C) stress.

Results

The DEGs (liver: 2186 to 3123; spleen 1542 to 2622) and up-regulated genes (liver: 1231 to 1776; spleen 769 to 1502) in the liver and spleen increased with the prolongation (12h to 48h) of poly (I:C)-stimulation time. This means L. lota needs to mobilize more functional genes in response to longer periods of poly (I:C)-stimulation. Despite the responses of L. lota to poly (I:C) showed tissue-specificity, we hypothesized that both liver and spleen of L. lota can respond to poly (I:C) challenge may be through promoting apoptosis of DNA-damaged cells, increasing the activity of immune-enhancing enzymes, and increasing energy supply based on DEGs annotation information.

Conclusions

Our results demonstrate the transcriptional responses of L. lota to poly (I:C)-stimulation, and these data provide the first resource on the genetic regulation mechanisms of L. lota against viruses. Furthermore, the present study can provide basic information for the prevention of viral diseases in L. lota artificial culture process.

New perspective on mechanism in muscle toxicity of ochratoxin A: Model of juvenile grass carp (Ctenopharyngodon idella)

Ochratoxin A (OTA) is a common fungal toxin that pollutes raw materials of aquatic feeds (such as corn, soybean meal, and wheat). This study explored the effects of OTA through diet on muscle toxicity in juvenile grass carp (Ctenopharyngodon idella). The following results were obtained for the muscle. (1) With an increase in dietary OTA, the residue of OTA in muscle increased, muscle fiber diameter and density decreased, and even muscle fiber breakage. (2) OTA caused oxidative stress by downregulating GPx1 (a, b) and Trx via inhibited the PGC1-α/Nrf2 signaling pathway. (3) OTA exacerbated endoplasmic reticulum stress in the muscle by causing endoplasmic reticulum expansion (results of transmission electron microscopy) and upregulating the expression of GRP78, eIF2α, ATF6, PERK, and CHOP. (4) OTA reduced muscle fiber diameter by inhibiting protein synthesis (AKT, TOR, and S6K1) and promoting the mRNA expression of protein degradation-related genes (MURF1, MAFBX, and FoxO3a), as well as by reducing AKT and promoting the immunofluorescence expression of FoxO3. (5) OTA inhibits collagen deposition by downregulating TGF-β1, TGF-βR1, Smad2, Smad3, Smad4, CTGF, TIMP, PHD, and LOX mRNA expressions as well as the CTGF immunofluorescence expression. Moreover, based on the GSH and collagen content contents, the upper safe dose for OTA-induced toxicity was 963.6 and 1129.6 μg/kg diet, respectively. Using the example of OTA, our research has provided new insights that raise concerns about the quality of aquatic products by exploring muscle toxicity caused by mycotoxins.

Oral bovine serum albumin administration alleviates inflammatory signals and improves antioxidant capacity and immune response under thioacetamide stress in blunt snout bream fed a high-calorie diet

This investigation looks at the impact of oral bovine serum albumin (BSA) on antioxidants, immune responses, and inflammation signals in blunt snout bream fed a high-calorie diet. 480 fish (average weight: 45.84 ± 0.07 g) were randomly fed a control diet, a high-fat diet (HFD), a high carbohydrate diet (HCD), and a high-energy diet (HED) in six replicates for 12 weeks. After the feeding trial, fish were orally administered with 10% BSA for 10 h, then blood and liver samples from five fish were randomly obtained after 10 h to determine plasma inflammatory markers and inorganic components. Also, the leftover fish were injected with thioacetamide, blood and liver samples were simultaneously obtained at 12, 48, and 96 h, respectively, to determine antioxidant, immune, and inflammatory signals, with survival rates recorded at the same time interval. After 10 h, plasma inflammatory markers such as tumour necrosis factors (TNF-α), interleukin 6 (IL6), nitric oxide (NO), Monocyte chemoattractant protein-1(MCP-1), and cortisol were significantly improved in fish fed HCD and HED as compared to the control. After thioacetamide stress, plasma lysozyme (LYM), complement 3, myeloperoxidase (MPO), and alkaline phosphatase activities, as well as immunoglobulin M, levels all increased significantly (P < 0.05) with increasing time with maximum value attained at 96 h, but shows no difference among dietary treatment. Similar results were observed in liver superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities and malondialdehyde (MDA) content, but tended to reduce at 96 h. nf-kb, tnf-α, and mcp-1 tend to decrease with the minimum value attained at 48 h and gradually decrease with increasing time at 96 h. After 96 h of the thioacetamide (TAA) challenge, the survival rate of blunt snout bream fed with an HFD and HCD was significantly lower (P < 0.05) at 48, and 96 h before the administration of BSA. However, no differences were observed among dietary treatments after the BSA administration. Overall, this study indicated that oral dietary administration of BSA might greatly enhance the antioxidant capability and innate immunity and mitigates inflammation signals after TAA stress in blunt snout bream fed high energy diet.

Integrative multiomics analysis of infant gut microbiome and serum metabolome reveals key molecular biomarkers of early onset childhood obesity

Evidence supports a complex interplay of gut microbiome and host metabolism as regulators of obesity. The metabolic phenotype and microbial metabolism of host diet may also contribute to greater obesity risk in children early in life. This study aimed to identify features that discriminated overweight/obese from normal weight infants by integrating gut microbiome and serum metabolome profiles. This prospective analysis included 50 South Asian children living in Canada, selected from the SouTh Asian biRth cohorT (START). Serum metabolites were measured by multisegment injection-capillary electrophoresis-mass spectrometry and the relative abundance of bacterial 16S rRNA gene amplicon sequence variant was evaluated at 1 year. Cumulative body mass index (BMI_AUC) and skinfold thickness (SSF_AUC) scores were calculated from birth to 3 years as the total area under the growth curve (AUC). BMI_AUC and/or SSF_AUC >85th percentile was used to define overweight/obesity. Data Integration Analysis for Biomarker discovery using Latent cOmponent (DIABLO) was used to identify discriminant features associated with childhood overweight/obesity. The associations between identified features and anthropometric measures were examined using logistic regression. Circulating metabolites including glutamic acid, acetylcarnitine, carnitine, and threonine were positively, whereas γ-aminobutyric acid (GABA), symmetric dimethylarginine (SDMA), and asymmetric dimethylarginine (ADMA) were negatively associated with childhood overweight/obesity. The abundance of the Pseudobutyrivibrio and Lactobacillus genera were positively, and Clostridium sensu stricto 1 and Akkermansia were negatively associated with childhood overweight/obesity. Integrative analysis revealed that Akkermansia was positively whereas Lactobacillus was inversely correlated with GABA and SDMA, and Pseudobutyrivibrio was inversely correlated with GABA. This study provides insights into metabolic and microbial signatures which may regulate satiety, energy metabolism, inflammatory processes, and/or gut barrier function, and therefore, obesity trajectories in childhood. Understanding the functional capacity of these molecular features and potentially modifiable risk factors such as dietary exposures early in life may offer a novel approach for preventing childhood obesity.

Dietary threonine improves muscle nutritional value and muscle hardness associated with collagen synthesis in grass carp (Ctenopharyngodon idella)

To further explain the improvement effect of threonine (Thr) on the fillet quality of fish, a 9-week feeding experiment was conducted. After feeding graded levels of Thr (2.38, 5.38, 8.38, 11.38, 14.38 and 17.38 g/kg), the compositions of fillet hydrolyzed amino acid and fatty acid, and the muscle hardness associated with collagen biosynthesis were mainly analyzed in grass carp (Ctenopharyngodon idella). The results showed that Thr increased the pH value, changed the amino acids and fatty acid composition of fillets, especially essential amino acid (EAA), C22:6n3 (DHA) and C20:5n3 (EPA). Furthermore, this study revealed for the first time that the improvement of muscle hardness by Thr was associated with collagen biosynthesis, and the TGF-β1/Smads, LARP6a and Hsp47 regulate transcriptional processes, translation initiation and post-translational modifications in collagen biosynthesis, respectively. This study offered a basis for exploring the contribution of Thr in improving muscle quality in sub-adult grass carp.

Aflatoxin B1 damaged structural barrier through Keap1a/Nrf2/ MLCK signaling pathways and immune barrier through NF-κB/ TOR signaling pathways in gill of grass carp (Ctenopharyngodon idella)

Aquafeeds are susceptible to contamination caused by aflatoxin B1 (AFB1). The gill of fish is an important respiratory organ. However, few studies have investigated the effects of dietary AFB1 exposure on gill. This study aimed to discuss the effects of AFB1 on the structural and immune barrier of grass carp gill. Dietary AFB1 increased reactive oxygen species (ROS) levels, protein carbonyl (PC) and malondialdehyde (MDA) contents, which consequently caused oxidative damage. In contrast, dietary AFB1 decreased antioxidant enzymes activities, relative genes expression (except MnSOD) and the contents of glutathione (GSH) (P < 0.05), which are partly regulated by NF-E2-related factor 2 (Nrf2/Keap1a). Moreover, dietary AFB1 caused DNA fragmentation. The relative genes of apoptosis (except Bcl-2, McL-1 and IAP) were significantly upregulated (P < 0.05), and apoptosis was likely upregulated through p38 mitogen-activated protein kinase (p38MAPK). The relative expressions of genes associated with tight junction complexes (TJs) (except ZO-1 and claudin-12) were significantly decreased (P < 0.05), and TJs were likely regulated by myosin light chain kinase (MLCK). Overall, dietary AFB1 disrupted the structural barrier of gill. Furthermore, AFB1 increased gill sensitivity to F. columnare, increased Columnaris disease and decreased the production of antimicrobial substances (P < 0.05) in grass carp gill, and upregulated the expression of genes involved with pro-inflammatory factors (except TNF-α and IL-8) and the pro-inflammatory response partly attributed to the regulation by nuclear factor κB (NF-κB). Meanwhile, the anti-inflammatory factors were downregulated (P < 0.05) in grass carp gill after challenge with F. columnare, which was partly attributed to the target of rapamycin (TOR). These results suggested that AFB1 aggravated the disruption of the immune barrier of grass carp gill after being challenge with F. columnare. Finally, the upper limit of safety of AFB1 for grass carp, based on Columnaris disease, was 31.10 μg/kg diet.

Selenium deficiency increased duodenal permeability and decreased expression of antimicrobial peptides by activating ROS/NF-κB signal pathway in chickens

Selenium (Se) is an essential trace element for the body. Various organs of the body, including the intestine, are affected by its deficiency. Se deficiency can induce oxidative stress and inflammatory responses in the intestine. It can also increase intestinal permeability and decrease intestinal immune function in mammals. However, the detailed studies, conducted on the intestinal molecular mechanisms of Se deficiency-induced injury in poultry, are limited. This study explored the adverse effects of Se deficiency on intestinal permeability and its mechanism. A Se-deficient chicken model was established, and the morphological changes in the chicken duodenum tissues were observed using a light microscope and transmission electron microscope (TEM). Western blotting, qRT-PCR, and other methods were used to detect the expression levels of selenoproteins, oxidative stress indicators, inflammatory factors, tight junction (TJ) proteins, antimicrobial peptides, and other related indicators in intestinal tissues. The results showed that Se deficiency could decrease the expression levels of selenoproteins and antioxidant capacity, activate the nuclear factor kappa-B (NF-κB) pathway, cause inflammation, and decrease the expression levels of TJ proteins and antimicrobial peptides in the duodenum tissues. The study also demonstrated that Se deficiency could increase intestinal permeability and decrease antimicrobial peptides via reactive oxygen species (ROS)/NF-κB. This study provided a theoretical basis for the scientific prevention and control of Se deficiency in poultry. Se deficiency decreased the expression levels of selenoproteins and increased ROS levels to activate the NF-κB pathway, resulting in the production of pro-inflammatory cytokines, reducing the expression levels of TJ protein, and weakening the expression of antimicrobial peptides, which contributed to the higher intestinal permeability. Oxidative stress weakened the expression of antimicrobial peptides.

Effects of Saline-Alkaline Stress on Metabolome, Biochemical Parameters, and Histopathology in the Kidney of Crucian Carp (Carassius auratus)

The salinization of the water environment caused by human activities and global warming has increased which has brought great survival challenges to aquatic animals. Crucian carp (Carassius auratus) is an essential freshwater economic fish with superior adaptability to saline-alkali water. However, the physiological regulation mechanism of crucian carp adapting to saline-alkali stress remains still unclear. In this study, crucian carp were exposed to freshwater or 20, 40, and 60 mmol/L NaHCO₃ water environments for 30 days, the effects of saline-alkali stress on the kidney were evaluated by histopathology, biochemical assays and metabolomics analysis from renal function, antioxidant capacity and metabolites level. Our results showed different degrees of kidney damage at different exposure concentrations, which were characterized by glomerular atrophy and swelling, renal tubular degranulation, obstruction and degeneration, renal interstitial edema, renal cell proliferation and necrosis. Saline-alkali stress could change the levels of several physiological parameters with renal function and antioxidant capacity, including creatinine (CREA), urea nitrogen (BUN), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA). In addition, metabolomics analysis showed that differential metabolites (DMs) were involved in various metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis, aminoacyl-tRNA biosynthesis, purine metabolism, glycerophospholipid metabolism, sphingolipid metabolism, glycolysis/gluconeogenesis and the TCA cycle. In general, our study revealed that saline-alkaline stress could cause significant changes in renal function and metabolic profiles, and induce severe damage in the crucian carp kidney through destroying the anti-oxidant system and energy homeostasis, inhibiting protein and amino acid catabolism, as well as disordering purine metabolism and lipid metabolism. This study could contribute to a deeper understanding the adverse effects of saline-alkali stress on crucian carp kidney and the regulatory mechanism in the crucian carp of saline-alkali adaptation at the metabolic level.

Dietary Aflatoxin B1 attenuates immune function of immune organs in grass carp (Ctenopharyngodon idella) by modulating NF-κB and the TOR signaling pathway

Aflatoxin B1 (AFB1) is kind of a common mycotoxin in food and feedstuff. Aquafeeds are susceptible to contamination of AFB1. In teleost fish, the spleen and head kidney are key immune organ. Moreover, the fish skin is a critical mucosal barrier system. However, there was little study on the effects of dietary AFB1 on the immune response of these immune organs in fish. This study aimed to explore the impacts of oral AFB1 on the immune competence and its mechanisms in the skin, spleen, and head kidney of grass carp. Our work indicated that dietary AFB1 reduced antibacterial compounds and immunoglobulins contents, and decreased the transcription levels of antimicrobial peptides in grass carp immune organs. In addition, dietary AFB1 increased the transcription levels of pro-inflammatory cytokines and reduced the transcription levels of anti-inflammatory cytokines in the grass carp immune organs, which might be regulated by NF-κB and TOR signaling, respectively. Meanwhile, we evaluated the content of AFB1 in the grass carp diet should not exceed 29.48 μg/kg diet according to the levels of acid phosphatase and lysozyme. In summary, dietary AFB1 impaired immune response in grass carp skin, spleen, and head kidney.

The multiple biotoxicity integrated study in grass carp (Ctenopharyngodon idella) caused by Ochratoxin A: Oxidative damage, apoptosis and immunosuppression

Ochratoxin A (OTA) is a common hazardous food contaminant that seriously endangers human and animal health. However, limited study is focused on aquatic animal. This research investigated the multiple biotoxicity of OTA on spleen (SP) and head kidney (HK) in grass carp and its related mechanism. Our data showed that, dietary supplemented with OTA above 1209 μg/kg caused histopathological damages by decreasing the number of lymphocytes and necrotizing renal parenchymal cells. Meanwhile, OTA caused oxidative damage and reduced the isoforms mRNAs transcripts of antioxidant enzymes (e.g., GPX1, GPX4, GSTO) partly due to suppressing NF-E2-related factor 2 (Nrf2). OTA triggered apoptosis through mitochondria and death receptor pathway potentially by p38 mitogen-activated protein kinase (p38MAPK) activation. Besides, OTA exacerbated inflammation by down-regulation of anti-inflammatory factor (e.g., IL-10, IL-4) and up-regulations of pro-inflammatory factors (e.g., TNF-α, IL-6), which could be ascribed to signaling meditation of Janus kinase / signal transducer and activator of transcription (JAK/STAT). Additionally, the safe upper limits of OTA were estimated to be 677.6 and 695.08 μg/kg based on the immune-related indexes (C3 contents in the SP and LZ activities in the HK, respectively). Our study has provided a wide insight for toxicological assessment of feed pollutant in aquatic animals.

Ultra-Performance Liquid Chromatography-Mass Spectrometry-Based Untargeted Metabolomics Reveals the Key Potential Biomarkers for Castor Meal-Induced Enteritis in Juvenile Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂)

The intensification of aquaculture to help kerb global food security issues has led to the quest for more economical new protein-rich ingredients for the feed-based aquaculture since fishmeal (FM, the ingredient with the finest protein and lipid profile) is losing its acceptability due to high cost and demand. Although very high in protein, castor meal (CM), a by-product after oil-extraction, is disposed-off due to the high presence of toxins. Concurrently, the agro-industrial wastes’ consistent production and disposal are of utmost concern; however, having better nutritional profiles of these wastes can lead to their adoption. This study was conducted to identify potential biomarkers of CM-induced enteritis in juvenile hybrid-grouper (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus♂) using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) alongside their growth and distal intestinal (DI) health evaluation. A total of 360 fish (initial weight = 9.13 ± 0.01g) were randomly assigned into three groups, namely, fish-meal (FM) (control), 4% CM (CM4), and 20% CM (CM20). After the 56-days feeding-trial, the DI tissues of FM, CM4, and CM20 groups were collected for metabolomics analysis. Principal components analysis and partial least-squares discriminant-analysis (PLS-DA, used to differentiate the CM20 and CM4, from the FM group with satisfactory explanation and predictive ability) were used to analyze the UPLC-MS data. The results revealed a significant improvement in the growth, DI immune responses and digestive enzyme activities, and DI histological examinations in the CM4 group than the others. Nonetheless, CM20 replacement caused DI physiological damage and enteritis in grouper as shown by AB-PAS staining and scanning electron microscopy examinations, respectively. The most influential metabolites in DI contents identified as the potential biomarkers in the positive and negative modes using the metabolomics UPLC-MS profiles were 28 which included five organoheterocyclic compounds, seven lipids, and lipid-like molecules, seven organic oxygen compounds, two benzenoids, five organic acids and derivatives, one phenylpropanoids and polyketides, and one from nucleosides, nucleotides, and analogues superclass. The present study identified a broad array of DI tissue metabolites that differed between FM and CM diets, which provides a valuable reference for further managing fish intestinal health issues. A replacement level of 4% is recommended based on the growth and immunity of fish.

Novel Insight Into Nutritional Regulation in Enhancement of Immune Status and Mediation of Inflammation Dynamics Integrated Study In Vivo and In Vitro of Teleost Grass Carp (Ctenopharyngodon idella): Administration of Threonine

This study aims to investigate the effects of threonine (Thr) on immunoregulation in vivo and in vitro of teleost grass carp (Ctenopharyngodon idella). Juveniles (9.53 ± 0.02 g) were reared for 8 weeks with respective Thr diet (3.99, 7.70, 10.72, 14.10, 17.96, and 21.66 g/kg) and then challenged with Aeromonas hydrophila for in vivo study. Macrophages isolated from head kidney were treated in vitro for 48 h with L-Thr (0, 0.5, 1.0, 2.0, 4.0, and 8.0 mM) after 6 h of lipopolysaccharide induction. The results showed that, compared with Thr deficiency (3.99 g/kg), the optimal dietary Thr (14.10g/kg) affected the immunocyte activation in the head kidney (HK) and spleen (SP) by downregulating the mRNA expressions of MHC-II and upregulating CD4 (not CD8), and it mediated the innate immune by enhancing the activities of lysozyme (LZ), acid phosphatase content of complement 3 (C3) and C4, increasing the mRNA abundances of hepcidin, liver expressed antimicrobial peptide-2A (LEAP-2A), LEAP-2B, β-defensin1, downregulating tumor necrosis factor α (TNF-α), IL-6, IL-1β, IL-12p35, IL-12p40, IL-17AF1, and IL-17D partly by attenuating RORγ1 transcriptional factor and nuclear factor kappa B p65 (NF-κBp65) signaling cascades [IKKβ/IκBα/NF-κBp65] and upregulating transforming growth factor β1 (TGF-β1), IL-4/13A, -4/13B, IL-10, and IL-22 partly by GATA-3. Besides these, the optimal dietary Thr regulated the adaptive immune by upregulating the mRNAs of immunoglobulin M (IgM) and IgZ (not IgD). Moreover, 2 mM Thr downregulated in vitro the mRNA abundances of colony stimulating factor-1, inducible nitric oxide synthase, mannose receptor 1, matrix metalloproteinase2 (MMP-2), and MMP-9 significantly (P < 0.05), indicating that Thr could attenuate the M1-type macrophages’ activation. Moreover, L-Thr downregulated the mRNA transcripts of TNF-α, IL-6, and IL-1β associated with impairing the SOCS1/STAT1 signaling and upregulated IL-10 and TGF-β1 partly by accentuating the SOCS3/STAT3 pathway. The above-mentioned observations suggested that Thr improved the immune status in the immune organs of fish by enhancing the immune defense and mediating the inflammation process. Finally, based on the immune indices of LZ activity in HK and C3 content in SP, the optimal Thr for immune enhancement in juvenile grass carp (9.53–53.43 g) was determined to be 15.70 g/kg diet (4.85 g/100 g protein) and 14.49 g/kg diet (4.47 g/100 g protein), respectively.

Transcriptome and metabolome analyses of the immune response to light stress in the hybrid grouper (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀)

Light intensity is an important environmental factor that affects fish growth and health through multiple physiological activities and metabolism and eventually impacts aquaculture harvest. There is a need to evaluate the fish stress response to light intensities, which will benefit aquaculture. Here, hybrid grouper (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀) was treated with three light intensities for evaluation of the light stress response, including high light intensity (1 250 lx), low light intensity (10 lx) and moderate light intensity (250 lx). Transcriptome analysis showed that a total of 71 318 unigene sequences were obtained with an N50 of 2 589 bp. Compared to the control group (250 lx), 1 697 differentially expressed genes (DEGs), a considerable quantity, were detected in the 1 250 lx group. Among those genes, 548 were upregulated, and the remaining 149 genes showed decreased expression. Comparatively small numbers of DEGs were detected in the 10 lx group; 54 out of 103 genes exhibited upregulated expression, and 49 genes showed downregulation. For further KEGG analysis, 82 DEGs were enriched in nine common signalling pathways in immunity, of which 73 DEGs were significantly inhibited in the 1 250 lx group. In contrast, only 11 DEGs were enriched in three immunity pathways, with nine DEGs showing a significant increase in the 10 lx group. The metabolome analysis revealed 59 and 44 differential metabolites (DMs) from the 1 250 lx and 10 lx groups, respectively. Of note, those DMs from the 1 250 lx-treated group were tendentiously involved in amino acid metabolism and lipid metabolism pathways, while the purine metabolism, amino acid metabolism and lipid metabolism pathways were mostly found in the 10 lx treatment group. In summary, our data indicated that high light intensity significantly inhibited the immune response in hybrid grouper, while low light intensity presented low stimulation of immune activity. In addition, both high and low light intensity could inhibit protein synthesis and amino acid metabolism. Taken together, hybrid grouper exhibited a much milder stress response to low light intensity than to high light intensity.

Identification of Small Molecules of the Infective Stage of Human Hookworm Using LCMS-Based Metabolomics and Lipidomics Protocols

Hookworm infections affect millions of people worldwide and are responsible for impaired mental and physical growth in children, and anemias. There is no vaccine, and increasing anthelmintic drug resistance in nematodes of domestic animals, and reduced drug cure rates in nematode infections of humans is alarming. Despite this looming health problem, there is a significant knowledge gap in terms of nonproteinaceous "excretory/secretory products" (ESPs) and how they orchestrate a parasitic existence. In the current study, we have conducted the first metabolomic and lipidomic analysis of the infective third-stage filariform larvae (L3) of the predominant human hookworm Necator americanus using liquid chromatography-mass spectrometry. Altogether, we have identified a total of 645 small molecules that were mainly produced through amino acid and glycerophospholipid metabolism. Putatively, 495 metabolites were unique to the somatic tissue extract, and 34 metabolites were present only in the ESP component. More than 21 novel mass features with nitrogen and sulfur functional groups were detected in the ESP component for the first time from helminths. While this study could not establish the biological functions of the metabolites identified, literature searches revealed that these metabolites possess various biological properties, including anti-inflammatory activities. These metabolites are likely used by the parasite upon exposure to a host to facilitate skin penetration, passage through different tissues, and immune regulation in the small bowel. Overall, the results presented herein offer significant insight into the metabolome of N. americanus L3 and have the potential to instigate future work to establish biomarkers of infection. This area urgently needs attention, given the lack of sensitive point-of-care diagnostic tools.

Dietary lipid levels affected antioxidative status, inflammation response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.)

A nine-week feeding trial was conducted to comprehensively investigate the effects of different levels of dietary lipid on intestinal physiology of juvenile turbot. Three diets with different lipid levels (8%, 12% and 16%) were formulated, which were designated as the low-lipid group (LL), medium-lipid group (ML) and high-lipid group (HL), respectively. Each diet was fed to six replicate tanks, and each tank was stocked with 35 fish. The results revealed that medium dietary lipid (12%) increased the activities of intestinal digestive enzymes and brush border enzymes. Excessive dietary lipid (16%) decreased the intestinal antioxidative enzyme levels and increased the lipid peroxidation pressure. In addition, HL stimulated the occurrence of intestinal inflammation and significantly up-regulated the mRNA expression level of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interferon-γ (IFN-γ) and transforming growth factor-β (TGF-β). Dietary LL and HL induced the apoptosis of intestinal epithelial cells. Sequencing of bacterial 16 s rRNA V4 region indicated that the abundance and diversity of intestinal microflora in fish fed with medium lipid diet (12%) were significantly higher than those in other groups, indicating the intestinal microflora ecology in group ML was more balanced. MetaStat analysis indicated that both low- and high-lipid diets significantly reduced the relative abundance of intestinal beneficial bacteria. In conclusion, results of this study demonstrated the sensitivity of intestinal health and microbiota to dietary lipid levels. From the perspective of microecological balance, medium dietary lipid (12%) was more conducive to maintaining the intestinal microflora stability of turbot.

Effects of dietary methionine on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis of on-growing grass carp (Ctenopharyngodon idella)

In the current research, a 60-d experiment was conducted with the purpose of exploring the impacts of methionine (Met) on growth performance, muscle nutritive deposition, muscle fibre growth and type I collagen synthesis as well as the related signalling pathway. Six diets (iso-nitrogenous) differing in Met concentrations (2·54, 4·85, 7·43, 10·12, 12·40 and 15·11 g/kg diets) were fed to 540 grass carp (178·47 (SD 0·36) g). Results showed (P < 0·05) that compared with Met deficiency, optimal level of dietary Met (1) increased feed intake, feed efficiency, specific growth rate and percentage weight gain (PWG); (2) increased fish muscle protein, lipid and free amino acid contents and improved fish muscle fatty acid profile as well as increased protein content in part associated with the target of rapamycin complex 1 (TORC1)/S6K1 signalling pathway; (3) increased the frequency distribution of muscle fibre with >50 µm of diameter; (4) increased type I collagen synthesis partly related to the transforming growth factor-β1/Smads and CK2/TORC1 signalling pathways. In conclusion, dietary Met improved muscle growth, which might be due to the regulation of muscle nutritive deposition, muscle fibre growth and type I collagen synthesis-related signal molecules. Finally, according to PWG and muscle collagen content, the Met requirements for on-growing grass carp (178-626 g) were estimated to be 9·56 g/kg diet (33·26 g/kg protein of diet) and 9·28 g/kg diet (32·29 g/kg of dietary protein), respectively.

Physiological Functions of Threonine in Animals: Beyond Nutrition Metabolism

Threonine (Thr), an essential amino acid for animals and the limiting amino acid in swine and poultry diets, which plays a vital role in the modulation of nutritional metabolism, macromolecular biosynthesis, and gut homeostasis. Current evidence supports that the supplementation of Thr leads to benefits in terms of energy metabolism. Threonine is not only an important component of gastrointestinal mucin, but also acts as a nutritional modulator that influences the intestinal immune system via complex signaling networks, particularly mitogen-activated protein kinase (MAPK) and the target of the rapamycin (TOR) signal pathway. Threonine is also recognized as an indispensable nutrient for cell growth and proliferation. Hence, optimization of Thr requirement may exert a favorable impact on the factors linked to health and diseases in animals. This review focuses on the latest reports of Thr in metabolic pathways and nutritional regulation, as well as the relationship between Thr and relevant physiological functions.

Dietary Betaine Mitigates Hepatic Steatosis and Inflammation Induced by a High-Fat-Diet by Modulating the Sirt1/Srebp-1/Pparɑ Pathway in Juvenile Black Seabream (Acanthopagrus schlegelii)

The present study aimed to elucidate the mechanism of dietary betaine, as a lipid-lowering substance, on the regulation of lipid metabolism and inflammation in juvenile black seabream (Acanthopagrus schlegelii) fed a high fat diet. An 8-week feeding trial was conducted in black seabream with an initial weight of 8.39 ± 0.01g fed four isonitrogenous diets including Control, medium-fat diet (11%); HFD, high-fat diet (17%); and HFD supplemented with two levels (10 and 20 g/kg) of betaine, HFD+B1 and HFD+B2, respectively. SGR and FE in fish fed HFD+B2 were significantly higher than in fish fed HFD. Liver histology revealed that vacuolar fat droplets were smaller and fewer in bream fed HFD supplemented with betaine compared to fish fed HFD. Betaine promoted the mRNA and protein expression levels of silent information regulator 1 (Sirt1), up-regulated mRNA expression and protein content of lipid peroxisome proliferator-activated receptor alpha (pparα), and down-regulated mRNA expression and protein content of sterol regulatory element-binding protein-1(srebp-1). Furthermore, the mRNA expression levels of anti-inflammatory cytokines in liver and intestine were up-regulated, while nuclear factor kB (nf-kb) and pro-inflammatory cytokines were down-regulated by dietary betaine supplementation. Likewise, in fish that received lipopolysaccharide (LPS) to stimulate inflammatory responses, the expression levels of mRNAs of anti-inflammatory cytokines in liver, intestine and kidney were up-regulated in fish fed HFD supplemented with betaine compared with fish fed HFD, while nf-kb and pro-inflammatory cytokines were down-regulated. This is the first report to suggest that dietary betaine could be an effective feed additive to alleviate hepatic steatosis and attenuate inflammatory responses in black seabream fed a high fat diet by modulating the Sirt1/Srebp-1/Pparɑ pathway.

Plasmatic Oxidative and Metabonomic Profile of Patients with Different Degrees of Biliary Acute Pancreatitis Severity

Acute pancreatitis (AP) is an inflammatory process of the pancreas with variable involvement of the pancreatic and peripancreatic tissues and remote organ systems. The main goal of this study was to evaluate the inflammatory biomarkers, oxidative stress (OS), and plasma metabolome of patients with different degrees of biliary AP severity to improve its prognosis. Twenty-nine patients with biliary AP and 11 healthy controls were enrolled in this study. We analyzed several inflammatory biomarkers, multifactorial scores, reactive oxygen species (ROS), antioxidants defenses, and the plasma metabolome of biliary AP and healthy controls. Hepcidin (1.00), CRP (0.94), and SIRI (0.87) were the most accurate serological biomarkers of AP severity. OS played a pivotal role in the initial phase of AP, with significant changes in ROS and antioxidant defenses relating to AP severity. Phenylalanine (p < 0.05), threonine (p < 0.05), and lipids (p < 0.01) showed significant changes in AP severity. The role of hepcidin and SIRI were confirmed as new prognostic biomarkers of biliary AP. OS appears to have a role in the onset and progression of the AP process. Overall, this study identified several metabolites that may predict the onset and progression of biliary AP severity, constituting the first metabonomic study in the field of biliary AP.

Lysine deficiency impaired growth performance and immune response and aggravated inflammatory response of the skin, spleen and head kidney in grown-up grass carp (Ctenopharyngodon idella)

This dissertation was primarily focused on the immune response, inflammatory response and molecular mechanisms in the skin, head kidney and spleen of grown-up grass carp (Ctenopharyngodon idella). Six iso-nitrogen diets differing in lysine concentrations (5.6, 8.5, 11.6, 14.4, 17.5 and 20.7 g/kg) were fed to 540 grass carp (164.85 ± 0.79 g) for 60 d. After that, grass carp were challenged by Aeromonas hydrophila for 6 d. This study revealed that lysine deficiency (1) suppressed the growth performance of the fish and decreased their ability to resist skin lesion morbidity, (2) impaired the immune organ^'s immune response by decreasing the gene expressions of mucin, liver-expressed antimicrobial peptide (LEAP)-2B, β-defensin-1 and LEAP-2A and the production of antibacterial compounds of grown-up grass carp, and (3) aggravated the inflammatory response of immune organs in the fish by increasing the gene expressions of pro-inflammatory cytokines (interferon γ2 [IFN-γ2], tumor necrosis factor α [TNF-α], interleukin [IL]-15, IL-17D, IL-12p40, IL-6 and IL-8) and down-regulating anti-inflammatory cytokines (IL-11, transforming growth factor β1 [TGF-β1], IL-10 and IL-4/13A), which were tightly correlated with signal transducer and activator of transcription (STAT)1 and STAT3 signaling pathway, respectively. The different phenomenon in the skin, spleen and head kidney of fish may be correlated with the difference in gene subtype. In addition, using quadratic regression analysis of percent weight gain (PWG), skin lesion morbidity, and the lysozyme activities in the spleen and head kidney, the dietary lysine requirements for grown-up grass carp were estimated to be 13.58, 13.51, 14.56 and 14.18 g/kg, respectively.

L-Threonine upregulates the expression of β-defensins by activating the NF-κB signaling pathway and suppressing SIRT1 expression in porcine intestinal epithelial cells

The use of antimicrobial peptide (AMP), found in all forms of life and playing a pivotal role in the innate immune system, has been developed as a new strategy for maintaining intestinal health and reducing antibiotic usage due to its ability to resist pathogens and commensal microbes. The current study investigated the effects of l-threonine on β-defensin expression, the intestinal mucosal barrier and inflammatory cytokine expression in porcine intestinal epithelial cell lines (IPEC-J2). The results revealed that in IPEC-J2 cells, l-threonine significantly increased the expression of β-defensin (including pBD-1, pBD-2, and pBD-3) in a dose- and time-dependent manner (P < 0.05). By using different concentrations and treatment times of l-threonine, the results showed that the expression of β-defensin was upregulated to the greatest extent in IPEC-J2 cells cultured with 1 mM l-threonine for 24 h. Although the mRNA expression levels of β-defensins were markedly increased (P < 0.05), there was relatively little inducible pBD-1, pBD-2 and pBD-3 mRNA expression at the sub-confluent and confluent densities in comparison with post-confluent densities. Furthermore, we found that l-threonine enhanced the β-defensin expression by suppressing the expression of SIRT1, which increased acetylated p65 expression, and activating the NF-κB signaling pathway, which induced the translocation of p65 from the cytoplasm to the nucleus. In addition, l-threonine significantly prevented LPS-induced intestinal mucosal barrier damage by attenuating the decreasing tendency of the mRNA expression of Mucin1 and Mucin2 (P < 0.05). Simultaneously, l-threonine enhanced the expression of β-defensins upon LPS challenge in IPEC-J2 cells (P < 0.05). l-Threonine obviously decreased the mRNA expression of inflammatory cytokines compared to that in untreated cells (P < 0.05). In conclusion, l-threonine can upregulate β-defensin expression and reduce inflammatory cytokine expression in IPEC-J2 cells; meanwhile, l-threonine alleviates LPS-induced intestinal mucosal barrier damage in porcine intestinal epithelial cells. The l-threonine-mediated modulation of endogenous defensin expression may be a promising approach to reduce antibiotic use, enhance disease resistance and intestinal health in animals.

Effects of Dietary Ochratoxin A on Growth Performance and Intestinal Apical Junctional Complex of Juvenile Grass Carp (Ctenopharyngodon idella)

Ochratoxin A (OTA) contamination widely occurs in various feed ingredients and food crops, potentially posing a serious health threat to animals. In this research, 1260 juvenile grass carp were separately fed with seven distinct experimental diets (0, 406, 795, 1209, 1612, 2003 and 2406 µg of OTA/kg of diet) for 60 consecutive days to evaluate OTA’s toxic effect on the intestinal apical junctional complex (including the tight junction (TJ) and the adherents junction (AJ)) and the underlying action mechanisms. Our experiment firstly confirmed that OTA caused fish growth retardation and disrupted the intestinal structural integrity. The detailed results show that OTA (1) depressed the feed efficiency, percentage weight gain and specific growth rate; (2) accumulated in the intestine; (3) caused oxidative damage and increased intestinal permeability; and (4) induced the RhoA/ROCK signaling pathway, destroying intestinal apical junctional complexes. Notably, OTA intervention did not result in changes in the gene expression of claudin-3c (in the proximal intestine (PI)), claudin-b and ZO-2b (in the mid intestine (MI) and distal intestine (DI)) in the fish intestine.

Modulation of Crustacean Innate Immune Response by Amino Acids and Their Metabolites: Inferences From Other Species

Aquaculture production of crustaceans (mainly shrimp and crabs) has expanded globally, but disease outbreaks and pathogenic infections have hampered production in the last two decades. As invertebrates, crustaceans lack an adaptive immune system and mainly defend and protect themselves using their innate immune system. The immune system derives energy and metabolites from nutrients, with amino acids constituting one such source. A growing number of studies have shown that amino acids and their metabolites are involved in the activation, synthesis, proliferation, and differentiation of immune cells, as well as in the activation of immune related signaling pathways, reduction of inflammatory response and regulation of oxidative stress. Key enzymes in amino acid metabolism have also been implicated in the regulation of the immune system. Here, we reviewed the role played by amino acids and their metabolites in immune-modulation in crustaceans. Information is inferred from mammals and fish where none exists for crustaceans. Research themes are identified and the relevant research gaps highlighted for further studies.

Metabolomes and Lipidomes of the Infective Stages of the Gastrointestinal nematodes, Nippostrongylus brasiliensis and Trichuris muris

Soil-transmitted helminths, including hookworms and whipworms, infect billions of people worldwide. Their capacity to penetrate and migrate through their hosts’ tissues is influenced by the suite of molecules produced by the infective developmental stages. To facilitate a better understanding of the immunobiology and pathogenicity of human hookworms and whipworms, we investigated the metabolomes of the infective stage of Nippostrongylus brasiliensis third-stage larvae (L3) which penetrate the skin and Trichuris muris eggs which are orally ingested, using untargeted liquid chromatography-mass spectrometry (LC-MS). We identified 55 polar metabolites through Metabolomics Standard Initiative level-1 (MSI-I) identification from N. brasiliensis and T. muris infective stages, out of which seven were unique to excretory/secretory products (ESPs) of N. brasiliensis L3. Amino acids were a principal constituent (33 amino acids). Additionally, we identified 350 putative lipids, out of which 28 (all known lipids) were unique to N. brasiliensis L3 somatic extract and four to T. muris embryonated egg somatic extract. Glycerophospholipids and glycerolipids were the major lipid groups. The catalogue of metabolites identified in this study shed light on the biology, and possible therapeutic and diagnostic targets for the treatment of these critical infectious pathogens. Moreover, with the growing body of literature on the therapeutic utility of helminth ESPs for treating inflammatory diseases, a role for metabolites is likely but has received little attention thus far.

Mannan oligosaccharides supplementation enhanced head-kidney and spleen immune function in on-growing grass carp (Ctenopharyngodon idella)

This research investigates the influences of dietary mannan oligosaccharides (MOS) on the head-kidney and spleen immune function in on-growing grass carp (Ctenopharyngodon idella) and its related mechanism. Fish were fed during 60 days at different levels of MOS (0, 200, 400, 600, 800 and 1000 mg kg^-1). Subsequently, 14 days after the feeding trial was injected intraperitoneally with Aeromonas hydrophila, the immune function was studied. The results are as follows: (1) appropriate MOS supplementation could increase the content of antibacterial compound and immunoglobulin (Ig), up-regulate antimicrobial peptides transcriptional levels in these two organs; (2) appropriate MOS supplementation attenuated inflammatory response in these two organs by regulating cytokines (pro- and anti-inflammatory cytokines) and related signalling pathways (NF-κB and TOR). The interesting points though, was, no differences were found in liver-expressed antimicrobial peptide (LEAP)-2A, interleukin (IL)-8, IL-4/13B, IκB kinase (IKK) α and nuclear factor kappa B (NF-κB) p52 gene expression in these two organs. Consequently, the present research suggests that MOS supplementation can enhance head-kidney and spleen immune function. Finally, we obtained these appropriate MOS dose (538.5 and 585.8 mg kg^-1) by quadratic regression analysis of lysozyme activity (head-kidney) and phosphatase activity (spleen), respectively.

Soybean glycinin impaired immune function and caused inflammation associated with PKC-ζ/NF-κb and mTORC1 signaling in the intestine of juvenile grass carp (Ctenopharyngodon idella)

Glycinin is a major protein and antinutritional factor of soybean. However, how dietary glycinin affect intestinal immune function of fish were largely unknown. In this study, we used juvenile grass carp as a model to investigate the impacts of glycinin on intestinal immune function of fish and involved mechanisms. We set three treatments including control, glycinin and glycinin + glutamine in this trial. For immune components, results revealed that compared with control group, glycinin group had lower acid phosphatase activities in the foregut, midgut and hindgut, lower C3 and C4 content, and lower mRNA abundances of IgM, IgZ, hepcidin, LEAP-2A, LEAP-2B and β-defensin-1 in the midgut and hindgut rather than foregut of grass carp. For pro-inflammatory cytokines and relevant signaling, glycinin elevated mRNA abundances of IL-1β, IL-8, IL-12p35, IL-12p40 and IL-17D in the midgut and IL-1β, IFN-γ2, IL-6, IL-8, IL-12p35, IL-12p40 and IL-17D in the hindgut, and increased protein abundances of PKC-ζ and nuclear NF-κB p65 in the midgut and hindgut in comparison to control. For anti-inflammatory cytokines and relevant signaling, glycinin reduced mRNA abundances of TGF-β1, TGF-β2, IL-4/13B (rather than IL-4/13A), IL-10 and IL-11 in the midgut and hindgut, and reduced p-mTOR (Ser 2448), p-S6K1 (Thr 389) and p-4EBP1 (Thr 37/46) protein abundances in the midgut and hindgut rather than foregut. Co-administration of glutamine with glycinin could partially enhance intestinal function and reduce intestinal inflammation compared with glycinin treatment. Concluded, glycinin decreased intestinal immune components and caused intestinal inflammation associated with PKC-ζ/NF-κB and mTORC1 signaling.

Preliminary study of mechanisms of intestinal inflammation induced by plant proteins in juvenile hybrid groupers (♀Epinephelus fuscoguttatus×♂E. lanceolatu)

Fish fed a high plant protein diet exhibit intestinal inflammation, the mechanism of which needs to be clarified. We preliminarily elucidate the mechanism of the TLRs/MyD88-PI₃K/Akt signalling pathway in intestinal inflammation induced by plant proteins. The diets contained 60% fish meal (FM, controls), or had 45% of the fish meal protein replaced by soybean meal (SBM), peanut meal (PM), cottonseed meal (CSM) or cottonseed protein concentrate (CPC). After an 8-week feeding trial, fish were challenged by injection of Vibrio parahaemolyticus bacteria for 7 days until the fish stabilized. The results showed that the specific growth rate (SGR) of the FM group was higher than other groups. The SGR of the CPC group was higher than those of the SBM, PM and CSM groups. The catalase (CAT) contents in the serum of fish fed a plant protein diet were higher than in FM fish. The abundances of Rhodobacteraceae and Microbacteriaceae in the MI (mid intestine) were higher in the CPC group. The TLR-2 expressions in the MI and DI of plant protein-fed fish were up-regulated. The expressions of IL-6 in the PI and MI, of hepcidin and TLR-3 in the MI, and of TLR-3 in the DI, were all lower than those of fish fed FM. In the PI, MI and DI, the protein expressions of P-PI₃K/T-PI₃K in the SBM and PM groups were higher than in the FM group. After the challenge, the cumulative mortalities in the FM and CPC groups were lower than those of the SBM, PM and CSM groups. These results suggested that plant protein diets reduced antioxidant capacity and glycolipid metabolism, hindered the development of the intestine and reduced intestinal flora diversity. TLR-3 is involved in the immune regulation of the PI in CPC group, MI and DI in SBM, PM, CSM and CPC groups, while might be involved in the immune regulation of the PI in SBM, PM and CSM groups. Furthermore, PI₃K/Akt signaling does not participate in the regulation of PI and MI in the CSM group, MI and DI in the CPC group.

Enzyme-treated soy protein supplementation in low protein diet enhanced immune function of immune organs in on-growing grass carp

A 56 days feeding trial was conducted to investigate the effects of enzyme-treated soy protein (ETSP) supplementation in low protein diets on immune function of immune organs (head kidney, spleen and skin) in on-growing grass carp. A total of 540 on-growing grass carp (initial average weight: 325.72 ± 0.60 g) were fed six diets, which included a normal protein diet (28% crude protein) and five low protein diets (26% crude protein) supplemented with graded levels of ETSP (0.0, 0.8, 1.2, 1.6 and 2.0%). At the end of feeding period, a challenge test was performed by infection with Aeromonas hydrophila for two weeks. The results indicated that (1) reducing dietary protein content from 28 to 26% decreased antibacterial substances and aggravated inflammatory responses of above three immune organs; (2) under the condition of reducing protein level in diet, 0.8-1.2% ETSP supplementation reversed these above adverse effects on immune function of above three immune organs; (3) suitable ETSP supplementation-decreased inflammatory responses were partly associated with [IκB kinase β (IKKβ)/inhibitor of κBα (IκBα)/nuclear factor kappa B (NF-κB) p65 and p52 or NF-κB p65] signaling and [target of rapamycin (TOR)/(S6K1, 4E-BP)] signaling in above three immune organs. (4) On the basis of C3 content (head kidney), C4 content (spleen) and skin hemorrhage and lesion, the optimal ETSP supplementation levels in low protein diets were estimated to be 1.48%, 1.61% and 1.03%, respectively. In summary, ETSP supplementation in low protein diets improved immune function of head kidney, spleen and skin in on-growing grass carp.

The dynamic process of dietary soybean β-conglycinin in digestion, absorption, and metabolism among different intestinal segments in grass carp (Ctenopharyngodon idella)

The present study aimed to investigate the dynamic process of soybean β-conglycinin in digestion, absorption, and metabolism in the intestine of grass carp (Ctenopharyngodon idella). Fish fed with 80 g β-conglycinin/kg diet for 7 weeks, the intestinal digestive enzyme was extracted to hydrolyze β-conglycinin in vitro, the free amino acid and its metabolism product contents in intestinal segments were analyzed. The present study first found that β-conglycinin cannot be thoroughly digested by fish intestine digestive enzyme and produces new products (about 60- and 55-kDa polypeptides). The indigestible β-conglycinin further caused the free amino acid imbalance, especially caused free essential amino acid deficiency in the proximal intestine but excess in the distal intestine. Moreover, these results might be partly associated with the effect of β-conglycinin in amino acid transporters and tight junction-regulated paracellular pathway. Finally, dietary β-conglycinin increased the content of amino acid catabolism by-product ammonia while decreased the amino acid anabolism product carnosine content in the proximal intestine and distal intestine. Thus, the current study first and systemically explored the dynamic process of β-conglycinin in digestion, absorption, and metabolism, which further supported our previous study that dietary β-conglycinin suppressed fish growth and caused intestine injure.

Molecular characterization and expression pattern of inositol-requiring enzyme 1 (IRE1) in blunt snout bream (Megalobrama amblycephala): its role of IRE1 involved in inflammatory response induced by lipopolysaccharide

This study aimed to characterize the full-length cDNA of IRE1 from fish Megalobrama amblycephala and investigate its role in the pro-inflammatory response. A full-length cDNA coding IRE1 was cloned from blunt snout bream by RT-PCR and RACE approaches. The cDNA obtained covered 3665 bp with an open reading frame of 3096 bp encoding 1031 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (74-92%) among various species, retaining one signal peptide, one luminal domain, one serine/threonine kinase domain, one RNase domain, one activation loop, two N-linked glycosylation sites, and several phosphorylation sites. The highest IRE1 expression was observed in the trunk kidney followed by the brain and spleen, whereas relatively low expression levels were detected in the liver, intestine, adipose, skin, and heart. After lipopolysaccharide (LPS) challenge, the expressions of glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1 (IRE1), spliced X-box binding protein 1 (XBP1s), C/EBP homologous protein (CHOP), nuclear factor kappa B (NF-κB), tumor necrosis factor alpha (TNFα), and interleukin-6 (IL-6) all increased remarkably in the spleen and brain at different sampling time points, while LPS also upregulated all the genes tested in the intestine except C/EBP homologous protein. Overall, the results indicated that the IRE1 gene of Megalobrama amblycephala shared a high similarity compared with other vertebrates including several bony fish species. Its expression in three tissues was induced remarkably by the LPS challenge, which indicated that IRE1 played a vital role in LPS-induced inflammation on fish.

Effects of acute ammonia toxicity on oxidative stress, DNA damage and apoptosis in digestive gland and gill of Asian clam (Corbicula fluminea)

Ammonia is one of the major pollutants associated with the main river basins due to ammonification of uneaten food and animal excretion, which usually brings detrimental health effects to aquatic invertebrate. However, the mechanisms of ammonia toxicity in aquatic invertebrate have rarely been reported. In this study, C. fluminea was exposed to different levels of ammonia (control group, 10 mg/L, and 25 mg/L) for 24 h and 48 h, and digestive gland and gill were collected to explore toxic effects on oxidative stress, DNA damage and apoptosis under ammonia stress. The results showed that ammonia poisoning could increase the activity of oxidative stress enzyme (SOD and CAT), inducing differentially expressed genes (DRAM2, GADD45, P53, BAX, BCL2, CASP8, CASP9, CASP3, HSP70 and HSP90) and different cytokines (IL-1 beta, IL-8, IL-17 and TNF-alpha) of DNA damage and apoptosis. The difference of toxic effects induced by ammonia among digestive gland and gill were also observed by real-time PCR and TUNEL staining. Our results will be helpful to understand the mechanism of aquatic toxicology induced by ammonia in C. fluminea.

Dietary biotin deficiency decreased growth performance and impaired the immune function of the head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella)

The aim of this study was to investigate the effects of dietary biotin deficiency on the growth performance and immune function of the head kidney, spleen and skin in on-growing grass carp (Ctenopharyngodon idella). A total of 540 on-growing grass carp (117.11 ± 0.48 g) were fed six diets containing increasing levels of biotin (0.012, 0.110, 0.214, 0.311, 0.427 and 0.518 mg/kg diet) for 70 days. Subsequently, a challenge experiment was performed by infecting them with Aeromonas hydrophila for six days. Our results showed that compared with the appropriate biotin level, (1) biotin deficiency (0.012 mg/kg diet) reduced the activities of lysozyme (LZ) and acid phosphatase (ACP), decreased the contents of complement 3 (C3), C4 and immunoglobulin M (IgM), as well as reduced the mRNA levels of antimicrobial peptides in the head kidney, spleen and skin of on-growing grass carp; (2) biotin deficiency reduced the mRNA levels of anti-microbial substances: liver-expressed antimicrobial peptide (LEAP) -2A, LEAP-2B, hepcidin, β-defensin-1 and mucin 2 in the head kidney, spleen and skin of on-growing grass carp; (3) biotin deficiency increased the mRNA levels of pro-inflammatory cytokines interleukin 1β (IL-1β), IL-6, IL-8, IL-12p40, IL-15, IL-17D, tumour necrosis factor α (TNF-α) and interferon γ2 (IFN-γ2) partially in association with nuclear factor-kappa B (NF-κB) signalling and reduced anti-inflammatory IL-4/13A, IL-10, IL-11 and transforming growth factor β1 (TGF-β1) mRNA levels partially in association with target of rapamycin (TOR) signalling in the head kidney, spleen and skin of on-growing grass carp. Interestingly, biotin deficiency had no effect on the expression of IL-12p35, IL-4/13B, TGF-β2, 4E-BP1 (skin only) or IKKα in the head kidney, spleen and skin of on-growing grass carp. In conclusion, the results indicated that biotin deficiency impaired the immune function of the head kidney, spleen and skin in fish. Finally, based on the percent weight gain (PWG), the ability to prevent skin haemorrhages and lesions, the LZ activity in the head kidney and the C4 content in the spleen, the optimal dietary biotin levels for on-growing grass carp (117-534 g) were estimated as 0.210, 0.230, 0.245 and 0.238 mg/kg diet, respectively.

Effect of dietary threonine on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

The experiment was conducted to investigate the effects of dietary threonine (Thr) on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. A total of 1200 fish (14·19 (se 0·13) g) were randomly distributed into six groups with four replicates each, fed six diets with graded level of Thr (9·5, 11·5, 13·5, 15·4, 17·4 and 19·3 g/kg diets) for 56 d. Results showed (P < 0·05) that dietary Thr (1) increased percentage weight gain, specific growth rate, feed efficiency and protein efficiency ratio; (2) up-regulated growth hormone (GH), insulin-like growth factor 1 (IGF-1), proliferating cell nuclear antigen, myogenic regulation factors (MyoD, Myf5, MyoG and Mrf4) and myosin heavy chain (MyHC) mRNA levels; (3) increased muscle protein content via regulating the protein kinase B/target of rapamycin signalling pathway and (4) decreased malondialdehyde and protein carbonyl contents, increased catalase, glutathione-S-transferase, glutathione reductase and GSH activities, up-regulated mRNA levels of antioxidant enzymes related to NFE2-related factor 2 and γ-glutamylcysteine ligase catalytic subunit. These results suggest that Thr has a potential role to improve muscle growth and protein synthesis, which might be due to the regulation of GH-IGF system, muscle growth-related gene, antioxidative capacity and protein synthesis-related signalling pathways. Based on the quadratic regression analysis of specific growth rate, the Thr requirement of hybrid catfish (14·19-25·77 g) was estimated to be 13·77 g/kg of the diet (33·40 g/kg of dietary protein).

Condensed tannins decreased the growth performance and impaired intestinal immune function in on-growing grass carp (Ctenopharyngodon idella)

The present study investigated the effects of condensed tannins (CT) on intestinal immune function in on-growing grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp were fed six diets containing different levels of CT (0, 10·00, 20·00, 30·00, 40·00 and 50·00 g/kg diet) for 70 d and then challenged with Aeromonas hydrophila for 14 d. The results showed that, compared with the control group, dietary CT (1) induced intestinal histopathological lesions and aggravated enteritis; (2) decreased lysozyme and acid phosphatase activities, complement 3 (C3), C4 and IgM contents and down-regulated the Hepcidin, liver-expressed antimicrobial peptide (LEAP)-2A, LEAP-2B, Mucin2 and β-defensin-1 mRNA levels in the proximal intestine (PI), mid intestine (MI) and distal intestine (DI) (P < 0·05); (3) down-regulated the mRNA levels of anti-inflammatory cytokines transforming growth factor (TGF)-β1, TGF-β2 (not in MI and DI), IL-4/13A (not IL-4/13B), IL-10 and IL-11 partly correlated with target of rapamycin (TOR) signalling; and (4) up-regulated the mRNA levels of pro-inflammatory cytokines interferon-γ2, IL-1β, IL-6, IL-8 (not in PI), IL-12p35, IL-12p40, IL-15 and IL-17D partly related to NF-κB signalling in the intestine of on-growing grass carp. Overall, the results indicated that CT could impair the intestinal immune function, and its potential regulation mechanisms were partly associated with the TOR and NF-κB signalling pathways. Finally, based on the percentage weight gain and enteritis morbidity, the maximum allowable levels of CT for on-growing grass carp (232·22-890·11 g) were estimated to be 18·6 and 17·4 g/kg diet, respectively.

Dietary choline supplementation attenuated high-fat diet-induced inflammation through regulation of lipid metabolism and suppression of NFκB activation in juvenile black seabream (Acanthopagrus schlegelii)

The present study aimed to investigate whether dietary choline can regulate lipid metabolism and suppress NFκB activation and, consequently, attenuate inflammation induced by a high-fat diet in black sea bream (Acanthopagrus schlegelii). An 8-week feeding trial was conducted on fish with an initial weight of 8·16 ± 0·01 g. Five diets were formulated: control, low-fat diet (11 %); HFD, high-fat diet (17 %); and HFD supplemented with graded levels of choline (3, 6 or 12 g/kg) termed HFD + C1, HFD + C2 and HFD + C3, respectively. Dietary choline decreased lipid content in whole body and tissues. Highest TAG and cholesterol concentrations in serum and liver were recorded in fish fed the HFD. Similarly, compared with fish fed the HFD, dietary choline reduced vacuolar fat drops and ameliorated HFD-induced pathological changes in liver. Expression of genes of lipolysis pathways were up-regulated, and genes of lipogenesis down-regulated, by dietary choline compared with fish fed the HFD. Expression of nfκb and pro-inflammatory cytokines in liver and intestine was suppressed by choline supplementation, whereas expression of anti-inflammatory cytokines was promoted in fish fed choline-supplemented diets. In fish that received lipopolysaccharide to stimulate inflammatory responses, the expression of nfκb and pro-inflammatory cytokines in liver, intestine and kidney were all down-regulated by dietary choline compared with the HFD. Overall, the present study indicated that dietary choline had a lipid-lowering effect, which could protect the liver by regulating intrahepatic lipid metabolism, reducing lipid droplet accumulation and suppressing NFκB activation, consequently attenuating HFD-induced inflammation in A. schlegelii.

l-Serine Lowers the Inflammatory Responses during Pasteurella multocida Infection

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida.

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida. Exogenous l-serine supplementation significantly increased the survival rate of mice and decreased the colonization of P. multocida in the lungs of mice. Notably, l-serine decreased the macrophage- and neutrophil-mediated inflammatory responses in mice during P. multocida infection.

Supplementation exogenous bile acid improved growth and intestinal immune function associated with NF-κB and TOR signalling pathways in on-growing grass carp (Ctenopharyngodon idella): Enhancement the effect of protein-sparing by dietary lipid

This study investigated the effects of bile acid (BA) supplementation on growth performance, intestinal immune function and the mRNA expression of the related signalling molecules in on-growing grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (mean weight 179.85 ± 1.34 g) were fed a normal protein and lipid (NPNL) diet containing 29% crude protein (CP) and 5% ether extract (EE), and five low-protein and high-lipid (LPHL) diets (26% CP, 6% EE) with graded levels of BA (0-320 mg/kg diet) for 50 days. The fish were then challenged with Aeromonas hydrophila for 14 days. The results indicated that compared with the NPNL diet, the LPHL diet (unsupplemented BA) suppressed the growth performance, intestinal development and enteritis resistance capability and impaired the partial intestinal immune function of on-growing grass carp. Whereas in the LPHL diet, optimal BA supplementation significantly improved fish growth performance (percent weight gain, specific growth rate, feed intake and feed efficiency) and intestinal growth and function (intestine weight, intestine length and intestosomatic index), increased beneficial bacteria Lactobacillus and Bifidobacterium amounts, decreased harmful bacteria Aeromonas and Escherichia coli amounts, elevated lysozyme and acid phosphatase activities, increased complement (C3 and C4) and immunoglobulin M contents, and upregulated β-defensin-1, hepcidin, liver expressed antimicrobial peptide 2A (LEAP-2A), LEAP-2B, Mucin2, interleukin 10 (IL-10), IL-11, transforming growth factor (TGF)-β1, TGF-β2, IL-4/13A (not IL-4/13B), TOR, S6K1 and inhibitor of κBα (IκBα) mRNA levels. In addition, optimal BA supplementation in the LPHL diet downregulated tumour necrosis factor α (TNF-α), interferon γ2 (IFN-γ2), IL-1β, IL-6, IL-8, IL-15, IL-17D, IL-12p35, IL-12p40 (rather than proximal intestine (PI) or mid intestine (MI), nuclear factor kappa B p65 (NF-κB p65) (except NF-κB p52), c-Rel, IκB kinase β (IKKβ), IKKγ (except IKKα), eIF4E-binding proteins (4E-BP)1 and 4E-BP2 mRNA levels in all three intestinal segments of on-growing grass carp (P < 0.05). These findings suggest that BA supplementation in the LPHL diet improves growth and intestinal immune function of fish. Furthermore, 240 mg/kg BA supplementation in the LPHL diet was superior to the NPNL diet in improving growth and enhancing intestinal immune function of fish. Finally, based on percent weight gain, feed intake, protecting fish against enteritis, lysozyme activity in MI and acid phosphatase activity in distal intestine (DI), the optimal BA supplementation for on-growing grass carp were estimated to be 168.98, 170.23, 166.67, 176.50 and 191.97 mg/kg diet, respectively.

Dietary gossypol reduced intestinal immunity and aggravated inflammation in on-growing grass carp (Ctenopharyngodon idella)

The present study explored the effects of dietary gossypol on the gut health of on-growing grass carp. The fish were fed six diets containing different levels of free gossypol (0, 121.38, 243.94, 363.89, 759.93 and 1162.06 mg/kg diet) from gossypol-acetic acid for 60 days and then challenged with Aeromonas hydrophila for 14 days. The results showed that dietary gossypol (1) could aggravate enteritis and damage the structure of intestinal epithelial cells, (2) decreased the lysozyme (LZ) and Acid phosphatase (ACP) activities, complement 3 (C3), C4 and immunoglobulin M (IgM) contents, and it down-regulated the Hepcidin (rather than distal intestine (DI)), immunoglobulin Z (IgZ), liver-expressed antimicrobial peptide (LEAP)-2B, Mucin2 and β-defensin-1 mRNA levels in the proximal intestine (PI), mid intestine (MI) and DI, (3) up-regulated intestinal pro-inflammatory cytokines tumor necrosis factor α (TNF-α), interferon γ2 (IFN-γ2), interleukin 1β (IL-1β), IL-6 (only in PI), IL-8 and IL-12p35 mRNA levels partly related to nuclear factor kappa B (NF-κB) signalling, and (4) down-regulated the mRNA levels of anti-inflammatory cytokines such as transforming growth factor (TGF)-β1, TGF-β2, interleukin 4/13A (IL-4/13A) (except IL-4/13B), IL-10 and IL-11 partly relating to target of rapamycin (TOR) signalling in the intestines of on-growing grass carp. Moreover, the dietary gossypol had no impact on the LEAP-2A, IL-12P40, IL-17D, IL-10, NF-κBp52, IKKα and eIF4E-binding proteins 2 (4E-BP2) mRNA levels in the intestines. Finally, based on the intestinal histopathological results, enteritis morbidity, LZ activity and IgM content, the safe dose of gossypol in the diets for on-growing grass carp should be less than 103.42 mg/kg diet.

Selenium deficiency impaired structural integrity of the head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella)

This study focused on the effects of dietary selenium deficiency on structural integrity of the head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (mean weight 226.48 ± 0.68 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of selenium (0.025-1.049 mg/kg diet) for 80 days. Results showed that selenium deficiency (1) caused oxidative damage in part by reducing the activities of antioxidant enzymes (such as SOD, CAT, GPx, GST and GR) and glutathione (GSH) content, down-regulating the transcript abundances of antioxidant enzymes (except GSTp1) partly related to Kelch-like-ECH-associated protein 1a (Keap1a)/NF-E2-related factor 2 (Nrf2) signalling; (2) aggravated apoptosis in part by up-regulating the mRNA levels of caspase-2, -3, -7, -8 and -9, which were partially related to p38MAPK/FasL/caspase-8 signalling and JNK/(BAX, Bcl-2, Mcl-1b, IAP)/(Apaf1, caspase-9) signalling; (3) damaged the tight junctions in part by down-regulating the mRNA levels of ZO-1 (except spleen), ZO-2 (except spleen), claudin-c, -f, -7, -11 and claudin-15, and up-regulating the mRNA levels of claudin-12, which were partially related to myosin light chain kinase (MLCK) signalling. Interesting, selenium deficiency failed to affect the expression of GSTp1, Keap1a, occludin, claudin-b, claudin-3c, ZO-1 (spleen only) and ZO-2 (spleen only) in the head kidney, spleen and skin of grass carp. Finally, based on the activities of glutathione peroxidase (GPx) and reactive oxygen species (ROS) content in the head kidney, spleen and skin, the dietary selenium requirements for young grass carp were estimated to be 0.558-0.588 mg/kg diet.

High-fat-diet-induced inflammation depresses the appetite of blunt snout bream (Megalobrama amblycephala) through the transcriptional regulation of leptin/mammalian target of rapamycin

The aim of this article was to investigate the mechanism of appetite suppression induced by high-fat diets (HFD) in blunt snout bream (Megalobrama amblycephala). Fish (average initial weight 40·0 (sem 0·35) g) were fed diets with two fat levels (6 and 11 %) with four replicates. HFD feeding for 30 d could significantly increase the weight gain rate, but feeding for 60 d cannot. Food intake of M. amblycephala began to decline significantly in fish fed the HFD for 48 d. HFD feeding for 60 d significantly reduced the expression of neuropeptide Y and elevated the expression of cocaine- and amphetamine-regulated transcript (CART), actions both in favour of suppression of appetite. The activation of fatty acid sensing was partly responsible for the weakened appetite. In addition, inflammatory factors induced by the HFD may be involved in the regulation of appetite by increasing the secretion of leptin and then activating the mammalian target of rapamycin (mTOR). Lipopolysaccharide (LPS, 2·0 mg/kg of fish weight) was administered to induce inflammation, and sampling was performed after 3, 6, 9, 12, 18, 24 and 48 h of LPS injection. Within 6-24 h of LPS injection, the food intake and appetite of M. amblycephala decreased significantly, whereas the mRNA expression of leptin and mTOR increased significantly. Our results indicate that inflammatory cytokines may be the cause of appetite suppression in M. amblycephala fed a HFD.

Dietary magnesium deficiency impaired intestinal structural integrity in grass carp (Ctenopharyngodon idella)

Grass carp (223.85–757.33 g) were fed diets supplemented with magnesium (73.54–1054.53 mg/kg) for 60 days to explore the impacts of magnesium deficiency on the growth and intestinal structural integrity of the fish. The results demonstrated that magnesium deficiency suppressed the growth and damaged the intestinal structural integrity of the fish. We first demonstrated that magnesium is partly involved in (1) attenuating antioxidant ability by suppressing Nrf2 signalling to decrease antioxidant enzyme mRNA levels and activities (except CuZnSOD mRNA levels and activities); (2) aggravating apoptosis by activating JNK (not p38MAPK) signalling to upregulate proapoptotic protein (Apaf-1, Bax and FasL) and caspase-2, -3, -7, -8 and -9 gene expression but downregulate antiapoptotic protein (Bcl-2, IAP and Mcl-1b) gene expression; (3) weakening the function of tight junctional complexes (TJs) by promoting myosin light chain kinase (MLCK) signalling to downregulate TJ gene expression [except claudin-7, ZO-2b and claudin-15 gene expression]. Additionally, based on percent weight gain (PWG), against reactive oxygen species (ROS), against caspase-9 and claudin-3c in grass carp, the optimal dietary magnesium levels were calculated to be 770.38, 839.86, 856.79 and 811.49 mg/kg, respectively.

Dietary myo-inositol deficiency decreased intestinal immune function related to NF-κB and TOR signaling in the intestine of young grass carp (Ctenopharyngodon idella)

In this study, we investigated the effects of dietary myo-inositol on the intestinal immune barrier function and related signaling pathway in young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp (221.33 ± 0.84 g) were fed six diets containing graded levels of myo-inositol (27.0, 137.9, 286.8, 438.6, 587.7 and 737.3 mg/kg) for 10 weeks. After the growth trial, fish were challenged with Aeromonas hydrophila. The results indicated that compared with the optimal dietary myo-inositol level, myo-inositol deficiency (27.0 mg/kg diet): (1) decreased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) contents in the proximal intestine (PI), middle intestine (MI) and distal intestine (DI) of young grass carp (P < 0.05). (2) down-regulated the mRNA levels of anti-microbial substance: liver expressed antimicrobial peptide (LEAP) 2A, LEAP-2B, hepcidin, β-defensin-1 and mucin2 in the PI, MI and DI of young grass carp (P < 0.05). (3) up-regulated pro-inflammatory cytokines [IL-1β (not in DI), TNF-α and IL-8], nuclear factor kappa B P65 (not NF-κB P52), c-Rel, IκB kinaseα (IKKα), IKKβ and IKKγ mRNA levels in the PI, MI and DI of young grass carp (P < 0.05); and down-regulated pro-inflammatory cytokines IL-15 (not in DI) and inhibitor of κBα (IκBα) mRNA levels (P < 0.05). (4) down-regulated the mRNA levels of anti-inflammatory cytokines [IL-10 (not in DI), IL-11, IL-4/13B (not IL-4/13A), TGF-β1 and TGF-β2], target of rapamycin (TOR), eIF4E-binding proteins 1 (4E-BP1) and ribosomal protein S6 kinase 1 (S6k1) in the PI, MI and DI of young grass carp (P < 0.05). All data indicated that myo-inositol deficiency could decrease fish intestine immunity and cause inflammation under infection of A. hydrophila. Finally, the optimal dietary myo-inositol levels for the ACP and LZ activities in the DI were estimated to be 415.1 and 296.9 mg/kg diet, respectively.