Dietary myo-inositol deficiency decreased the growth performances and impaired intestinal physical barrier function partly relating to nrf2, jnk, e2f4 and mlck signaling in young grass carp (Ctenopharyngodon idella)

Myo-inositol: A potential game-changer in preventing gill cell death and alleviating "gill rot" in grass carp (Ctenopharyngodon idellus)

Increasing evidence shows the potential threat of gill rot in freshwater fish culture. F. columnare is wide-spread in aquatic environments, which can cause fish gill rot and result in high mortality and losses of fish. This study investigated the effects of myo-inositol (MI) on the proliferation, structural integrity, and different death modes of grass carp (Ctenopharyngodon idella) gill epithelial cells, as well as its possible mechanism. 30 mg/L MI up-regulated CCK8 OD value and the protein level of solute carrier family 5A 3 (SLC5A3), and down-regulated the reactive oxygen species (ROS) content in gill cells and lactate dehydrogenase (LDH) release in the culture medium (P < 0.05). MI up-regulated the protein level of Beclin1, the protein level and fluorescence expression of microtubule-associated protein light chain 3B (LC3B) and down-regulated the protein level of sequestosome-1 (SQSTM1, also called p62) (P < 0.05). MI down-regulated the protein levels of Cysteine aspartate protease-1 (caspase-1), Gasdermin E (GSDME) and Cleaved interleukin 1 beta (IL-1β) (P < 0.05). MI up-regulated the protein level of caspase-8 (P < 0.05), but had no effect on apoptosis (P > 0.05). MI down-regulated the mRNA expressions and protein levels of tumor necrosis factor α (tnfα), TNF receptor 1 (tnfr1), receptor interacting protein 1 (ripk1), receptor interacting protein 3 (ripk3) and mixed lineage kinase domain-like protein (mlkl), and reduce the ratio of p-MLKL/MLKL (P < 0.05). The addition of MI or necrosulfonamide (NSA) alone, or the addition of MI after induction of necroptosis, significantly up-regulated the cell activity and the protein level of SLC5A3 in gill cells, and significantly reduced the LDH release in the culture medium and the intracellular ROS content, the number of necroptosis cells, the protein expression of TNFα, TNFR1 and RIPK1, and the ratio of p-RIPK3/RIPK3 and p-MLKL/MLKL (P < 0.05). It indicated MI induce autophagy may relate to Beclin1/LC3/p62 signaling pathway, inhibits pyroptosis may attribute to Caspase-1/GSDMD/IL-1β signaling pathway, and inhibits necroptosis via MLKL signaling pathway. However, MI had no effect on apoptosis.

An emerging role of arecoline on growth performance, intestinal digestion and absorption capacities and intestinal structural integrity of adult grass carp (Ctenopharyngodon idella)

Arecoline is an alkaloid with important pharmacological effects in the plant areca nut, which has been demonstrated to be an agonist of muscarinic receptors (M receptor). This study explored the influences of dietary arecoline on growth performance, intestinal digestion and absorption abilities, antioxidant capacity, and the apical junction complex (AJC) of adult grass carp (Ctenopharyngodon idella). Adult grass carp (608 to 1512 g) were fed at 6 graded levels of dietary arecoline (0, 0.5, 1.0, 1.5, 2.0, and 2.5 mg/kg diet) for 9 weeks. The results suggested that appropriate dietary supplementation of arecoline (1.0 mg/kg) increased growth parameters and intestinal growth in adult grass carp (P < 0.05), enhanced digestion and absorption capacities (P < 0.05), up-regulated muscarinic receptor 3 (M3) mRNA level (P < 0.05), increased the content of neuropeptide fish substance P (P < 0.05), improved antioxidant capacity by activating the Keap1a/Nrf2 signaling pathway (P < 0.05), reduced intestinal mucosal permeability (P < 0.05), and increased mRNA levels of tight junction (TJ) and adherent junction AJ-related proteins in fish by inhibiting the RhoA/ROCK signaling pathway (RhoA/ROCK/MLCK/NMII) (P < 0.05). In addition, the appropriate arecoline supplementation for adult grass carp was determined to be 1.20, 1.21, 1.07, and 1.19 mg/kg based on percentage weight gain, lipase activity, serum diamine oxidase, and protein carbonyl, respectively. Overall, to the best of our knowledge, we investigated for the first time the effects and possible mechanisms of dietary arecoline on intestinal digestive and absorptive capacities and structural integrity in fish and evaluated the appropriate level of supplementation.

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.

Exogenous inositol ameliorates the effects of acute ammonia toxicity on intestinal oxidative status, immune response, apoptosis, and tight junction barriers of great blue-spotted mudskippers (Boleophthalmus pectinirostris)

Ammonia toxicity can disrupt the intestinal health of aquatic animals. It is important to find substances that alleviate these adverse effects. The present study explored the possible protective role of myo-inositol (MI) in ammonia-induced toxicity in the fish intestine. Great blue-spotted mudskippers (Boleophthalmus pectinirostris) accumulated in artificial seawater (15‰ salinity, n = 600) were randomly selected and intraperitoneally injected with NaCl (0.68%) or MI (2.5 mg/g fish in 0.68% NaCl) then exposed to artificial seawater alone (NaCl and MI group) or seawater containing 57.025 mmol/L ammonium chloride (NH₃ and NH₃ + MI group). After a 24-h experiment, it showed that ammonia exposure down-regulated the mRNA expression levels of intestinal barrier function proteins (Zo-1, Ocln, Cldn-5, Cldn-12, and Cldn-15) and anti-inflammatory cytokines (Tgf-β and Il-10) while the acute ammonia stress up-regulated the apoptosis genes (p53, Bax, Caspase-3, and Caspase-9) and pro-inflammatory cytokines (Tnf-α and Il-1β). Furthermore, ammonia challenge also induced oxidative stress, as the malondialdehyde and the protein carbonyl contents were increased. In addition, ammonia stress down-regulated the antioxidant enzymes (Cu/Zn-Sod, Cat, Gpx, and Gst) activities as well as their gene transcription levels. The administration of the exogenous myo-inositol greatly ameliorated the ammonia-induced changes in redox capacity, immune response, apoptosis, inflammation, and tight junction barrier function to levels similar to those of the NaCl group. Furthermore, fish injected with MI alone showed no significant changes compared with the NaCl group. Taken together, pretreatment with myo-inositol had no obvious side-effects and effectively protected the mudskippers' intestine from the toxicity caused by acute ammonia stress.

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.

The regulatory effects of pyridoxine deficiency on the grass carp (Ctenopharyngodon idella) gill barriers immunity, apoptosis, antioxidant, and tight junction challenged with Flavobacterium columnar

The effects of dietary pyridoxine (PN) on the gill immunity, apoptosis, antioxidant and tight junction of grass cap (Ctenopharyngodon idella) were investigated in this study. Fish were fed semi-purified diets containing graded levels of PN for 10 weeks, and then challenged with Flavobacterium columnare by bath immersion exposure for 3 days. The results indicated that compared with the optimal PN level, PN deficiency resulted in a decline in the antimicrobial compound production of gill. In addition, PN deficiency up-regulated the pro-inflammatory cytokines and down-regulated the anti-inflammatory cytokines gene expression, which might be associated with the enhanced nuclear factor κB p65 and the inhibited target of rapamycin signalling pathways, respectively, suggesting that PN deficiency could impair gill immune barrier function. Furthermore, PN deficiency (1) induced cell apoptosis, which may be partly associated with the (apoptotic protease activating factor-1, Bcl-2 associated X protein)/caspase-9 and c-Rel/tumor necrosis factor α (rather than FasL)/caspase-8 mediated apoptosis pathway. (2) Inhibited Kelch-like ECH-associating protein 1a/NF-E2-related factor 2 mRNA expression, decreased the mRNA expression and activities of antioxidant enzymes, increased the levels of reactive oxygen species, protein carbonyl and malondialdehyde. (3) Increased the mRNA expression level of myosin light chain kinase, which may be result in the down-regulation of tight junction complexes such as zonula occludens 1, occludin and claudins (expect claudin-12 and claudin-15). These results suggest that PN deficiency could impair gill physical barrier function. In summary, dietary PN deficiency could cause the impairment of gill barrier function associated with immunity, apoptosis, antioxidant and tight junction, which may result in the increased the susceptibility of fish to pathogenic bacteria. Moreover, based on the gill rot morbidity, LZ activity and MDA content, the dietary PN requirements for grass cap were estimated to be 4.85, 4.78 and 4.77 mg kg^-1 diet, respectively.

Efficient production of myo-inositol in Escherichia coli through metabolic engineering

BACKGROUND

The biosynthesis of high value-added compounds using metabolically engineered strains has received wide attention in recent years. Myo-inositol (inositol), an important compound in the pharmaceutics, cosmetics and food industries, is usually produced from phytate via a harsh set of chemical reactions. Recombinant Escherichia coli strains have been constructed by metabolic engineering strategies to produce inositol, but with a low yield. The proper distribution of carbon flux between cell growth and inositol production is a major challenge for constructing an efficient inositol-synthesis pathway in bacteria. Construction of metabolically engineered E. coli strains with high stoichiometric yield of inositol is desirable.

RESULTS

In the present study, we designed an inositol-synthesis pathway from glucose with a theoretical stoichiometric yield of 1 mol inositol/mol glucose. Recombinant E. coli strains with high stoichiometric yield (> 0.7 mol inositol/mol glucose) were obtained. Inositol was successfully biosynthesized after introducing two crucial enzymes: inositol-3-phosphate synthase (IPS) from Trypanosoma brucei, and inositol monophosphatase (IMP) from E. coli. Based on starting strains E. coli BW25113 (wild-type) and SG104 (ΔptsG::glk, ΔgalR::zglf, ΔpoxB::acs), a series of engineered strains for inositol production was constructed by deleting the key genes pgi, pfkA and pykF. Plasmid-based expression systems for IPS and IMP were optimized, and expression of the gene zwf was regulated to enhance the stoichiometric yield of inositol. The highest stoichiometric yield (0.96 mol inositol/mol glucose) was achieved from recombinant strain R15 (SG104, Δpgi, Δpgm, and RBSL5-zwf). Strain R04 (SG104 and Δpgi) reached high-density in a 1-L fermenter when using glucose and glycerol as a mixed carbon source. In scaled-up fed-batch bioconversion in situ using strain R04, 0.82 mol inositol/mol glucose was produced within 23 h, corresponding to a titer of 106.3 g/L (590.5 mM) inositol.

CONCLUSIONS

The biosynthesis of inositol from glucose in recombinant E. coli was optimized by metabolic engineering strategies. The metabolically engineered E. coli strains represent a promising method for future inositol production. This study provides an essential reference to obtain a suitable distribution of carbon flux between glycolysis and inositol synthesis.

Novel insights into the intestinal immune regulatory effects of (2-Carboxyethyl) dimethylsulfonium Bromide (Br-DMPT) in on-growing grass carp (Ctenopharyngodon idella)

The present study evaluated the effects of (2-Carboxyethyl)dimethylsulfonium Bromide (Br-DMPT) supplementation on the intestinal immune function and potential mechanisms of on-growing grass carp (Ctenopharyngodon idella) by feeding fish (initial weight 216.49 ± 0.29 g) five diets with gradational Br-DMPT (0-520 mg/kg diet) concentrations for 60 days and then infecting them with Aeromonas hydrophila for 14 days. Our results firstly indicated that compared with the control group, appropriate Br-DMPT supplementation increased the number of beneficial bacteria Lactobacillus and Bifidobacterium and enteritis resistance, decreased the number of detrimental bacteria Aeromonas and E. coli, and relieved the intestinal histopathological symptoms of fish. In addition, compared with the control group, appropriate Br-DMPT supplementation (1) increased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) content; (2) upregulated the mRNA levels of anti-microbial substance: liver expressed anti-microbial peptide (LEAP) -2A, LEAP-2B, hepcidin, β-defensin-1 and Mucin2; (3) partially downregulated 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)] by inhibiting [IKKβ/IκBα/(NF-κBp65 and c-Rel)] signalling; and (4) partially upregulated the mRNA levels of anti-inflammatory cytokines [IL-4/13A, IL-10, IL-11, transforming growth factor (TGF)-β1] by activating [TOR/(S6K1 and 4E-BP)] signalling. The aforementioned results indicated that appropriate amount of Br-DMPT exerted a positive effect on the regulation of intestinal immune function in fish. Finally, based on enteritis morbidity, the IgM content and the lysozyme activity in the PI, the appropriate levels of Br-DMPT supplementation for on-growing grass carp were established as 295.43, 301.73 and 320.36 mg/kg diet, respectively.

Myo-inositol: its metabolism and potential implications for poultry nutrition-a review

Myo-inositol (MI) has gained relevance in physiology research during the last decade. As a constituent of animal cells, MI was proven to be crucial in several metabolic and regulatory processes. Myo-inositol is involved in lipid signaling, osmolarity, glucose, and insulin metabolism. In humans and rodents, dietary MI was assessed to be important for health so that MI supplementation appeared to be a valuable alternative for treatment of several diseases as well as for improvements in metabolic performance. In poultry, there is a lack of evidence not only related to specific species-linked metabolic processes but also about the effects of dietary MI on performance and health. This review intends to provide information about the meaning of dietary MI in animal metabolism as well as to discuss potential implications of dietary MI in poultry health and performance with the aim to identify open questions in poultry research.

Soybean β-conglycinin caused intestinal inflammation and oxidative damage in association with NF-κB, TOR and Nrf2 in juvenile grass carp (Ctenopharyngodon idella): varying among different intestinal segments

The current study aimed to investigate the effects and mechanisms of dietary soybean β-conglycinin in immune function and oxidative damage among different intestinal segments of juvenile grass carp (Ctenopharyngodon idella). 240 fish (13.77 ± 0.10 g) were fed control or 8% β-conglycinin diet for 7 weeks. Dietary β-conglycinin caused inconsistent suppression effects on the innate immune by decreasing complement component, lysozyme, antimicrobial peptide and acid phosphatase among different intestinal segments. Meanwhile, dietary β-conglycinin caused inflammation in the mid and distal intestine by raising pro-inflammatory cytokines and declining anti-inflammatory cytokines mRNA levels, while more serious in the distal intestine than in the mid intestine. Furthermore, dietary β-conglycinin regulating inflammatory cytokines might be associated with transcription factors nuclear factor-κB P65 (NF-κB P65) nucleus translocation and target of rapamycin (TOR) phosphorylation in the distal intestine but only related to TOR phosphorylation in the mid intestine. Interestingly, in the proximal intestine, dietary β-conglycinin decreased both pro-inflammatory and anti-inflammatory cytokines mRNA level, and did not affect NF-κB P65 nucleus translocation and TOR phosphorylation. For oxidative damage, dietary β-conglycinin exposure elevated both malondialdehyde (MDA) and protein carbonyl (PC) contents in the distal intestine, which might be attributed to the suppression of the Mn-SOD, catalase (CAT) and glutathione peroxidase (GPx) activities. In the mid intestine, dietary β-conglycinin only increased PC content in association with the low activities of CAT, GPx and glutathione peroxidase (GR). Unexpectedly, in the proximal intestine, dietary β-conglycinin did not significantly change MDA and PC contents while decreased antioxidant enzyme activities. Furtherly, dietary β-conglycinin affect the antioxidant enzyme activity might be regulated by the varying pattern of nuclear factor-erythroid 2-related factor 2 (Nrf2) nucleus translocation among these three intestinal segments. In summary, dietary β-conglycinin caused intestinal inflammation and oxidative damage in association with NF-κB, TOR and Nrf2 signaling molecules, which were varying among the three intestinal segments of grass carp.

Myo-inositol in the protection from cadmium-induced toxicity in mice kidney: An emerging nutraceutical challenge

Cadmium (Cd) induces functional and morphological changes in kidney. Therefore, the effects of a natural nutraceutical antioxidant, myo-inositol (MI), were evaluated in mice kidneys after Cd challenge. Twenty-eight C57 BL/6 J mice were divided into these groups: 0.9% NaCl; MI (360 mg/kg/day); CdCl₂ (2 mg/kg/day) plus vehicle; CdCl₂ (2 mg/kg/day) plus MI (360 mg/kg/day). After 14 days, kidneys were processed for structural, biochemical and morphometric evaluation. Treatment with CdCl₂ increased urea nitrogen and creatinine in serum and augmented tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) expression. Furthermore, monocyte chemoattractant protein-1 (MCP-1), kidney injury molecule-1 (KIM-1) and myo-inositol oxygenase (MIOX) immunoreactivity, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells number were significantly higher than control and MI groups. Glutathione (GSH) content and glutathione peroxidase (GPx) activity were reduced and structural changes were evident. The treatment with MI significantly lowered urea nitrogen and creatinine levels, TNF-α and iNOS expression, MCP-1, KIM-1 and MIOX immunoreactivity and TUNEL positive cells number, increased GSH content and GPx activity and preserved kidney morphology. A protection of MI against Cd-induced damages in mice kidney was demonstrated, suggesting a strong antioxidant role of this nutraceutical against environmental Cd harmful effects on kidney lesions.

Effects of Dietary Zearalenone on Oxidative Stress, Cell Apoptosis, and Tight Junction in the Intestine of Juvenile Grass Carp (Ctenopharyngodon idella)

Zearalenone (ZEA) is a prevalent mycotoxin with high toxicity in animals. In order to study its effect on juvenile grass carp (Ctenopharyngodon idella), six diets supplemented with different levels of ZEA (0, 535, 1041, 1548, 2002, and 2507 μg/kg diet) for 10 weeks were studied to assess its toxicity on intestinal structural integrity and potential mechanisms of action. Our report firstly proved that ZEA led to growth retardation and body deformity, and impaired the intestinal structural integrity of juvenile grass carp, as revealed by the following findings: (1) ZEA accumulated in the intestine and caused histopathological lesions; (2) ZEA resulted in oxidative injury, apoptosis, and breached tight junctions in the fish intestine, which were probably associated with Nuclear factor-erythroid 2-related factor 2 (Nrf2), p38 mitogen activated protein kinases (p38MAPK), and myosin light chain kinase (MLCK) signaling pathways, respectively. ZEA had no influence on the antioxidant gene levels of Kelch-like ECH associating protein 1 (Keap1)b (rather than Keap1a), glutathione-S-transferase (GST)P1, GSTP2 (not in the distal intestine (DI)), tight junctions occludin, claudin-c (not in the proximal intestine (PI)), or claudin-3c (not in the mid intestine (MI) or DI).

Vitamin A deficiency impairs intestinal physical barrier function of fish

The present study was the first to investigate the effects of dietary vitamin A (VA) on the intestinal physical barrier function associated with oxidation, antioxidant system, apoptosis and cell-cellular tight junction (TJ) in the proximal (PI), mid (MI) and distal (DI) intestines of young grass carp (Ctenopharyngodon idella). Fish were fed graded levels of dietary VA for 10 weeks, and then a challenge test using an injection of Aeromonas hydrophila was conducted for 14 days. Results indicated that dietary VA deficiency caused oxidative damage to fish intestine partly by the reduced non-enzymatic antioxidant components glutathione (GSH) and VA contents as well as reduced antioxidant enzyme activities [not including manganese superoxide dismutase (MnSOD)]. Further results observed that the decreased antioxidant enzyme activities by VA deficiency were partly related to the down-regulation of their corresponding mRNA levels which were regulated by the down-regulation of NF-E2-related factor 2 (Nrf2) mRNA levels and up-regulation of kelch-like-ECH-associated protein (Keap1a) (rather than Keap1b) mRNA levels in three intestinal segments of fish. Meanwhile, VA deficiency up-regulated the mRNA levels of the apoptosis signalling [caspase-3, caspase-8, caspase-9 (rather than caspase-7)] associated with the inhibition of the target of rapamycin (TOR) signalling pathway in three intestinal segments of fish. Additionally, VA deficiency decreased the mRNA levels of TJ complexes [claudin-b, claudin-c, claudin-3, claudin-12, claudin-15a, occludin and zonula occludens-1 (ZO-1) in the PI, MI and DI, as well as claudin-7 and claudin-11a in the MI and DI] linked to the up-regulation of myosin light chain kinase (MLCK) signalling. These results suggested that VA deficiency impaired structural integrity in three intestinal segments of fish. Meanwhile, excessive VA also showed similar negative effects on these indexes. Taken together, the current study firstly demonstrated that VA deficiency impaired physical barrier functions associated with impaired antioxidant capacity, aggravated cell apoptosis and disrupted TJ complexes in the PI, MI and DI, but different segments performed different actions in fish. Based on protecting fish against protein oxidation, the optimal VA levels for grass carp were estimated to be 2622 IU/kg diet.

Deoxynivalenol decreased intestinal immune function related to NF-κB and TOR signalling in juvenile grass carp (Ctenopharyngodon idella)

Deoxynivalenol (DON) is one of the most common mycotoxins in animal feed worldwide and causes significant threats to the animal production. The intestine is an important mucosal immune organ in teleost, and it is also the first target for feed-borne toxicants in animal. However, studies concerning the effect of DON on fish intestine are scarce. This study explored the effects of DON on intestinal immune function in juvenile grass carp (Ctenopharyngodon idella). A total of 1440 juvenile grass carp (12.17 ± 0.01 g) were fed six diets containing graded levels of DON (27, 318, 636, 922, 1243 and 1515 μg/kg diet) for 60 days. After the growth trial, fish were challenged with Aeromonas hydrophila. The results were analysed by the Duncan's multiple-range test (P < 0.05), indicating that compared with the control group (27 μg/kg diet), dietary DON levels up to 318 μg/kg diet: (1) decreased lysozyme (LZ) and acid phosphatase (ACP) activities, as well as complement 3 (C3), C4 and immunoglobulin M (IgM) content in the proximal intestine (PI), middle intestine (MI) and distal intestine (DI) of juvenile 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 juvenile grass carp (P < 0.05); (3) up-regulated the mRNA levels of pro-inflammatory cytokines [interleukin 1β (IL-1β), tumour necrosis factor α (TNF-α), interferon γ2 (INF-γ2), IL-6 (only in PI), IL-8, IL-12p35, IL-12p40, IL-15 and IL-17D] in the PI, MI and DI of juvenile grass carp (P < 0.05), which might be partly related to nuclear factor kappa B (NF-κB) signalling [IκB kinase β (IKKβ) and IKKγ/inhibitor of κBα (IκBα)/NF-κB (p65 and c-Rel)]; and (4) down-regulated the mRNA levels of anti-inflammatory cytokines [IL-10, IL-11, IL-4/13A (not IL-4/13B), transforming growth factor β1 (TGF-β1) (not TGF-β2)] in the PI, MI and DI of juvenile grass carp (P < 0.05), which might be partly related to target of rapamycin (TOR) signalling [TOR/ribosomal protein S6 kinases 1 (S6K1) and eIF4E-binding proteins (4E-BP)]. All data indicated that DON could impair the intestinal immune function, and its potential regulation mechanisms were partly associated with NF-κB and TOR signalling pathways. Finally, based on the enteritis morbidity, and the LZ and ACP activities as well as IgM content in the PI, the reasonable dose of DON for grass carp were estimated to be 251.66, 305.83, 252.34 and 309.94 μg/kg diet, respectively.

Deoxynivalenol decreased the growth performance and impaired intestinal physical barrier in juvenile grass carp (Ctenopharyngodon idella)

Deoxynivalenol (DON) is one of the most common mycotoxin contaminants of animal feed worldwide and brings significant threats to the animal production. However, studies concerning the effect of DON on fish intestine are scarce. This study explored the effects of DON on intestinal physical barrier in juvenile grass carp (Ctenopharyngodon idella). A total of 1440 juvenile grass carp (12.17 ± 0.01 g) were fed six diets containing graded levels of DON (27, 318, 636, 922, 1243 and 1515 μg/kg diet) for 60 days. This study for the first time documented that DON caused body malformation in fish, and histopathological lesions, oxidative damage, declining antioxidant capacity, cell apoptosis and destruction of tight junctions in the intestine of fish. The results indicated that compared with control group (27 μg/kg diet), DON: (1) increased the reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC) content, and up-regulated the mRNA levels of Kelch-like-ECH-associated protein 1 (Keap1: Keap1a but not Keap1b), whereas decreased glutathione (GSH) content and antioxidant enzymes activities, and down-regulated the mRNA levels of antioxidant enzymes (except GSTR in MI) and NF-E2-related factor 2 (Nrf2), as well as the protein levels of Nrf2 in fish intestine. (2) up-regulated cysteinyl aspartic acid-protease (caspase) -3, -7, -8, -9, apoptotic protease activating factor-1 (Apaf-1), Bcl2-associated X protein (Bax), Fas ligand (FasL) and c-Jun N-terminal protein kinase (JNK) mRNA levels, whereas down-regulated B-cell lymphoma-2 (bcl-2) and myeloid cell leukemia-1 (Mcl-1) mRNA levels in fish intestine. (3) down-regulated the mRNA levels of ZO-1, ZO-2b, occludin, claudin-c, -f, -7a, -7b, -11 (except claudin-b and claudin-3c), whereas up-regulated the mRNA levels of claudin-12, -15a (not -15b) and myosin light chain kinase (MLCK) in fish intestine. All above data indicated that DON caused the oxidative damage, apoptosis and the destruction of tight junctions via Nrf2, JNK and MLCK signaling in the intestine of fish, respectively. Finally, based on PWG, FE, PC and MDA, the safe dose of DON for grass carp were all estimated to be 318 μg/kg diet.

Optimal α-lipoic acid strengthen immunity of young grass carp (Ctenopharyngodon idella) by enhancing immune function of head kidney, spleen and skin

This study was for the first time to investigate the effects of α-lipoic acid (LA) on growth and immune function of head kidney, spleen and skin in young grass carp (Ctenopharyngodon idella). A total of 540 healthy grass carp (with initial body weight at 216.59 ± 0.33 g) were randomly divided into six groups and fed six separate diets with graded dietary levels of LA for 70 days. Un-supplemented group did not find LA and its concentrations in the other five diets were 203.25, 403.82, 591.42, 781.25 and 953.18 mg kg^-1, respectively. After the growth trial, fish were challenged with A. hydrophila for 14 days. The results showed that, compared with the un-supplemented group, optimal LA improved lysozyme (LZ) and acid phosphatase (ACP) activities, enhanced complement 3 (C3), C4 and immunoglobulin (Ig) M contents and up-regulated hepcidin, liver expressed antimicrobial peptide (LEAP)-2A, LEAP-2B and β-defensin-1 mRNA levels in the head kidney, spleen and skin of young grass carp; meanwhile, optimal LA up-regulated anti-inflammatory cytokines transforming growth factor (TGF)-β1, TGF-β2, interleukin (IL)-4/13A (not IL-4/13B), IL-10 and IL-11 mRNA levels partly related to target of rapamycin (TOR) signaling and down-regulated pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interferon (IFN)-γ2, IL-1β, IL-6, IL-8, IL-12p40 (not IL-12p35), IL-15 (not in the skin) and IL-17D mRNA levels partially associated with nuclear factor-kappa B (NF-κB) signaling in the head kidney, spleen and skin of young grass carp. Above results indicated that optimal LA enhanced the immune function of head kidney, spleen and skin in fish. Interestingly, excessive LA decreased the growth and impaired the immune function of head kidney, spleen and skin in fish. Finally, on the basis of the percent weight gain (PWG), the ability against skin hemorrhage and lesion, the IgM content in the head kidney and the LZ activity in the spleen, the optimal dietary LA levels were estimated to be 315.37, 382.33, 353.19 and 318.26 mg kg^-1 diet, respectively.

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.

Deficiency of dietary pyridoxine disturbed the intestinal physical barrier function of young grass carp (Ctenopharyngodon idella)

The aim of this study was to assess the effects of dietary pyridoxine (PN) deficiency on intestinal antioxidant capacity, cell apoptosis and intercellular tight junction in young grass carp (Ctenopharyngodon idella). A total of 540 young grass carp (231.85 ± 0.63 g) were fed six diets containing graded levels of PN (0.12-7.48 mg/kg diet) for 10 weeks. At the end of the feeding trial, the fish were challenged with Aeromonas hydrophila for 2 weeks. The results showed that compared with the optimal PN level, PN deficiency (1) increased the contents of reactive oxygen species (ROS), malondialdehyde (MDA) and protein carbonyl (PC), decreased the activities and mRNA levels of antioxidant enzymes such as copper, zinc superoxide dismutase (CuZnSOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) (P < .05); (2) up-regulated the mRNA levels of cysteinyl aspartic acid-protease-3 (caspase-3), caspase-7, caspase-8, caspase-9, Bcl-2 associated X protein (Bax), apoptotic protease activating factor-1 (Apaf-1) and Fas ligand (FasL), and down-regulated the mRNA levels of inhibitor of apoptosis proteins (IAP), B-cell lymphoma protein-2 (Bcl-2) and myeloid cell leukaemia-1 (Mcl-1) (P < .05); (3) down-regulated the mRNA levels of ZO-1, occludin [only in middle intestine (MI)], claudin-b, claudin-c, claudin-f, claudin-3c, claudin-7a, claudin-7b and claudin-11, and up-regulated the mRNA levels of claudin-12 and claudin-15a (P < .05), which might be partly linked to Kelch-like-ECH-associated protein 1a (Keap1a)/NF-E2-related factor 2 (Nrf2), p38 mitogen-activated protein kinase (p38MAPK) and myosin light chain kinase (MLCK) signalling in the intestines of fish. However, the activities and mRNA levels of MnSOD, the mRNA levels of Keap1b, c-Jun N-terminal protein kinase (JNK) and claudin-15b in three intestinal segments, and the mRNA levels of occludin in the proximal intestine (PI) and distal intestine (DI) were not affected by graded levels of PN. These data indicate that PN deficiency could disturb the intestinal physical barrier function of fish. Additionally, based on the quadratic regression analysis for MDA content and GST activity, the dietary PN requirements for young grass carp were estimated as 4.85 and 5.02 mg/kg diet, respectively.

Sodium butyrate enhanced physical barrier function referring to Nrf2, JNK and MLCK signaling pathways in the intestine of young grass carp (Ctenopharyngodon idella)

This study evaluated the effect of dietary sodium butyrate (SB) supplementation on the intestinal physical barrier function of young grass carp (Ctenopharyngodon idella). The fish were fed one powdery sodium butyrate (PSB) diet (1000.0 mg kg^-1 diet) and five graded levels of microencapsulated sodium butyrate (MSB) diets: 0.0 (control), 500.0, 1000.0, 1500.0 and 2000.0 mg kg^-1 diet for 60 days. Subsequently, a challenge test was conducted by injection of Aeromonas hydrophila to explore the effect of SB supplementation on intestinal physical barrier function and the potential mechanisms in fish. The results showed that optimal SB supplementation: (1) down-regulated the cysteine-aspartic protease-2 (caspase-2), caspase-3 (rather than PI), caspase-7, caspase-8 (rather than PI), caspase-9, fatty acid synthetase ligand (FasL), apoptotic protease activating factor-1 (Apaf-1), B-cell lymphoma 2 associated X protein (Bax) and c-Jun Nterminal protein kinase (JNK) mRNA levels, up-regulated the B-cell lymphoma protein-2 (Bcl-2) (rather than PI), inhibitor of apoptosis proteins (IAP) and myeloid cell leukemia-1 (Mcl-1) mRNA levels in the intestine (P < 0.05), inhibited the intestinal cell apoptosis, maintained the intestine cell structure integrity; (2) increased NF-E2-related factor 2 (Nrf2) mRNA levels and nucleus protein levels, and down-regulated kelch-like-ECH-associated protein (Keap1b) (rather than Keap1a) mRNA levels in the intestine, up-regulated copper/zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), catalase (CAT), glutathione peroxidase 1a (GPx1a), GPx1b, GPx4a, GPx4b, glutathione S-transferases R (GSTR), GSTP1, GSTP2, GSTO1, GSTO2 and glutathione reductase (GR) mRNA levels in the intestine, increased the corresponding antioxidant enzymes activity (P < 0.05), thus enhancing the ability of scavenging free radicals and decreasing the reactive oxygen species (ROS) content, decreasing the lipid and protein peroxidation, as well as alleviating oxidative damage; (3) down-regulated the molecule myosin light-chain kinase (MLCK) mRNA levels in the intestine, and up-regulated the occludin, zonula occludens-1 (ZO-1), ZO-2, claudin-b, claudin-c, claudin-f, claudin-3c (rather than PI), claudin-7a, claudin-7b and claudin-11 mRNA levels, down-regulated claudin-12, claudin-15a and claudin-15b mRNA levels (P < 0.05), thus maintaining the structural integrity between cells. This study suggests that SB supplementation could improve fish intestinal physical barrier function. Furthermore, according to the positive effect, MSB was superior to PSB on improving intestinal physical barrier function of fish. Finally, based on protein carbonyl content in the PI, the optimal SB supplementation (MSB as SB source) for young grass carp was estimated to be 338.8 mg kg^-1 diet.