Effects of dietary arginine on antioxidant status and immunity involved in AMPK-NO signaling pathway in juvenile blunt snout bream

A Study on the Function of Arginine in the Growth, Immunity, Antioxidant Activity, and Oxygen Carrying-Capacity of Juvenile Gibel Carp (Carassius auratus gibelio)

An eight-week trial was designed to study the effects of arginine (Arg) supplemented diets on the growth, immunity, antioxidant activity, and oxygen-carrying capacity of juvenile Gibel carp (Carassius auratus gibelio). A total of 300 fish (27.53 ± 0.03 g) were randomized into 15 equal groups and fed on diets with graded Arg levels: 0 (control), 0.2%, 0.4%, 0.6%, and 0.8% (w/w). The results showed that final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR) all increased and then declined with increasing levels of Arg supplementation, while feed conversion ratio (FCR) showed the opposite trend. In addition, the fish's whole-body crude protein and ash content had no remarkable difference at different levels of Arg addition (p > 0.05). Supplementation with 0.6% and 0.8% Arg significantly increased plasma alanine transaminase (ALT) activity (p < 0.05). The malondialdehyde (MDA) levels and superoxide dismutase (SOD) activities of the liver were not significantly different between the different levels of Arg supplementation (p > 0.05), while catalase (CAT) activity was significantly increased with 0.4% Arg supplementation levels (p < 0.05). The 0.8% Arg supplementation greatly increased the expression of hepatic-related genes to the Nrf2 signaling pathway, including sod and gpx (p < 0.05). However, the 0.8% Arg supplementation did not significantly increase the relative expression of genes related to the NF-κB signaling pathway, including il-1β, il-8, and tnf-α (p > 0.05). Similarly, the relative expression of hif-1 signaling pathway-related genes at 0.8% Arg supplementation was significantly elevated, including hif-1α, epo, and vegf (p < 0.05). Hence, Arg supplementation could promote growth and improve immune, antioxidant, and oxygen-carrying capacity in juvenile Gibel carp.

Dietary arginine regulates the growth performance, antioxidant capacity, and immune response in Culter alburnus

Culter alburnus is sensitive to stressors. Arginine is a precursor of nitric oxide, which can effectively relieve the level of oxidative stress and improve the antioxidant and immune capacity of fish. The effect of different arginine levels on topmouth culter (Culter alburnus) fry development performance, liver antioxidant capacity, and immune parameters were investigated in this study. Five diets (1.96%, ARG1, control group; 2.28%, ARG2; 2.52%, ARG3; 2.81%, ARG4; 3.09%, ARG5) were used to feed fry (initial weight 0.31 ± 0.01 g) for 8 weeks. The data showed that the final weight (FW), weight gain rate (WGR), and specific growth rate (SGR) of the ARG3 and ARG4 groups were significantly improved, while the feed conversion ratio (FCR) reduced significantly. Compared with the ARG1 group, all groups remarkably reduced the crude ash content of the whole body. The activity of hepatic superoxide dismutase (SOD) and the content of hepatic glutathione (GSH) were significantly increased in the ARG3 and ARG4 groups, while the malondialdehyde (MDA) content was significantly decreased. Compared with the ARG1 group, arginine levels in ARG2, ARG3, and ARG4 groups up-regulated the expression levels of Nrf2, down-regulated the gene expression level of Keap1 in the liver. And the expression of Nrf2/Keap1 pathway downstream genes Mn-SOD and CAT was up-regulated in ARG2 and ARG3 groups. Furthermore, the expression levels of MyD88 and IL-1β were down-regulated, and the anti-inflammatory gene TGF-β expression levels were up-regulated in the ARG2, ARG3, and ARG4 groups. Additionally, compared to the ARG1 group, there was a significant increase in the relative expression levels of the C3 and C4 genes in the ARG4 group. In conclusion, 2.28-2.81% dietary arginine levels improved the growth performance, promoted antioxidant capacity, and enhance immune response. The optimal level of arginine was determined by the quadratic regression analysis of SGR and FCR to be 2.55% of diet (5.43% of dietary protein) and 2.53% of diet (5.38% of dietary protein), accordingly.

Alterations in certain immunological parameters in the skin mucus of the carp, Cirrhinus mrigala, infected with the bacteria, Edwardsiella tarda

The bacterial fish pathogen Edwardsiella tarda causes heavy stock mortality, severely hampering fish production, resulting in great economic loss to the farming industry. The first biological barriers that confer immune protection against pathogen entry are the fish mucosal surfaces. The present study was undertaken to investigate the influence of E. tarda on certain enzymatic and non-enzymatic parameters in the skin mucous secretions of the fish Cirrhinus mrigala using spectrophotometry and zymography. Fish were randomly divided into three groups: control, vehicle control, and infected. A sublethal dose of E. tarda (2.2 × 106 CFU/fish) suspended in 50 μL of PBS was injected intra-peritoneally at 0 day (d). Subsequently, mucus samples were collected at 2 d, 4 d, 6 d and 8 d post-infection. The activities of lysozyme (LYZ), protease (PROT), alkaline phosphatase (ALP), acid phosphatase (ACP), catalase (CAT), peroxidase (PER), superoxide dismutase (SOD), and glutathione S-transferase (GST) decreased significantly in the skin mucus of the challenged fish, indicating the suppressed immune system and decreased antioxidant capacity of C. mrigala to E. tarda infection. Lipid peroxidation (LPO) and total nitrate-nitrite were significantly higher at several time points post-infection, suggesting that physiological functions have been impaired following pathogen challenge. The present findings could be relevant for fish aquaculture and underline the importance of skin mucus not only for assessing fish immune status but also for identifying early warning signals of disease caused by pathogens.

Dietary Soybean Lecithin Improves Growth, Immunity, Antioxidant Capability and Intestinal Barrier Functions in Largemouth Bass Micropterus salmoides Juveniles

This study evaluated the effects of dietary soybean lecithin (SBL) on the growth, haematological indices, immunities, antioxidant capabilities, and inflammatory and intestinal barrier functions because little information of dietary SBL could be obtained in juvenile largemouth bass (Micropterus salmoides). The fish were fed identical diets except for SBL added at 0, 2, 4 and 8%. It was found that 4 and 8% SBL significantly increased fish weight gain and daily growth rate (p < 0.05), while 4% SBL was optimal for enhancing RBC, HGB, PLT, MCV, MCH, WBC and MON in blood, and ALB and ALP in serum (p < 0.05). SBL (4%) also significantly elevated the antioxidant enzymes activities of T-SOD, CAT, GR, GPx, GST and T-AOC and GSH contents; increased mRNA transcription levels of Nrf2, Cu/Zn-SOD, CAT, GR, GST3 and GPx3; and decreased MDA contents. Keap1a and Keap1b levels were markedly down-regulated (p < 0.05). SBL (4%) significantly enhanced levels of the immune factors (ACP, LZM and C3) and the mRNA expression levels of innate immune-related genes (C3, C4, CFD, HEPC and MHC-I) compared with the control groups (0%) (p < 0.05). SBL (4%) significantly increased IgM and T-NOS in the intestine (p < 0.05) and significantly decreased levels of TNF-α, IL-8, IL-1β and IFN-γ and increased TGF-β1 at both transcription and protein levels in the liver and intestine (p < 0.05). The mRNA expression levels of MAPK13, MAPK14 and NF-κB P65 were significantly decreased in the intestine in the 4% SBL groups (p < 0.05). Histological sections also demonstrated that 4% SBL protected intestinal morphological structures compared with controls. This included increased intestinal villus height and muscular thickness (p < 0.05). Furthermore, the mRNA expression levels of the intestinal epithelial cell tight junction proteins (TJs) (ZO-1, claudin-3, claudin-4, claudin-5, claudin-23 and claudin-34) and mucin-5AC were significantly up-regulated in the 4% SBL groups compared with the controls (p < 0.05). In conclusion, these results suggested that 4% dietary SBL could not only improve growth, haematological indices, antioxidant capabilities, immune responses and intestinal functions, but also alleviate inflammatory responses, thereby providing reference information for the feed formulations in cultured largemouth bass.

Histidine Deficiency Inhibits Intestinal Antioxidant Capacity and Induces Intestinal Endoplasmic-Reticulum Stress, Inflammatory Response, Apoptosis, and Necroptosis in Largemouth Bass (Micropterus salmoides)

This 56-day study aimed to evaluate the effects of histidine levels on intestinal antioxidant capacity and endoplasmic-reticulum stress (ERS) in largemouth bass (Micropterus salmoides). The initial weights of the largemouth bass were (12.33 ± 0.01) g. They were fed six graded levels of histidine: 0.71% (deficient group), 0.89%, 1.08%, 1.26%, 1.48%, and 1.67%. The results showed that histidine deficiency significantly suppressed the intestinal antioxidant enzyme activities, including SOD, CAT, GPx, and intestinal level of GSH, which was supported by significantly higher levels of intestinal MDA. Moreover, histidine deficiency significantly lowered the mRNA level of nrf2 and upregulated the mRNA level of keap1, which further lowered the mRNA levels of the downstream genes sod, cat, and gpx. Additionally, histidine-deficiency-induced intestinal ERS, which was characterized by activating the PEPK-signalling pathway and IRE1-signalling pathway, including increased core gene expression of pepk, grp78, eif2α, atf4, chopα, ire1, xbp1, traf2, ask1, and jnk1. Dietary histidine deficiency also induced apoptosis and necroptosis in the intestine by upregulating the expressions of proapoptotic genes, including caspase 3, caspase 8, caspase 9, and bax, and necroptosis-related genes, including mlkl and ripk3, while also lowering the mRNA level of the antiapoptotic gene bcl-2. Furthermore, histidine deficiency activated the NF-κB-signalling pathway to induce an inflammatory response, improving the mRNA levels of the proinflammatory factors tnf-α, hepcidin 1, cox2, cd80, and cd83 and lowering the mRNA levels of the anti-inflammatory factors tgf-β1 and ikbα. Similarly, dietary histidine deficiency significantly lowered the intestinal levels of the anti-inflammatory factors TGF-β and IL-10 and upregulated the intestinal levels of the proinflammatory factor TNF-α, showing a trend similar to the gene expression of inflammatory factors. However, dietary histidine deficiency inhibited only the level of C3, and no significant effects were observed for IgM, IgG, HSP70, or IFN-γ. Based on the MDA and T-SOD results, the appropriate dietary histidine requirements of juvenile largemouth bass were 1.32% of the diet (2.81% dietary protein) and 1.47% of the diet (3.13% dietary protein), respectively, as determined by quadratic regression analysis.

Rice protein suppresses 4-hydroxy-2-nonenal-induced inflammation owing to methionine availability

4-Hydroxy-2-nonenal (HNE) is one of the most important products of lipid peroxidation which induces inflammation. In order to investigate the effect of rice protein (RP) on suppressing HNE-induced inflammation and the role of methionine in regulating the anti-inflammatory function of RP, Wistar rats (male, weighing180-200 g) were ad libitum fed either a pellet diet with oral administration of methionine or ad libitum fed RP for two weeks. RP and methionine significantly reduced HNE levels and effectively suppressed the expressions of cyclooxygenase-2, tumor necrosis factor alpha, interleukin (IL)-1β, IL-6, and inducible nitric oxide synthase. The anti-inflammatory action of RP was evident from the upregulation of IL-10 and glutathione S-transferase, which played a role in the detoxification of HNE. The results show that the molecular mechanism responsible for the anti-inflammatory function of RP is the inhibition of nuclear factor-κB activation by the downregulation of protein kinase B/phosphoinositide 3 kinase. Further, this study demonstrates that methionine availability contributes to the suppression of HNE-induced inflammation through up-regulating IL-10 and GST in rats fed RP. Novelty: RP suppresses HNE-induced inflammation. Met plays a role in up-regulating IL-10 and GST. Met availability regulates the inhibition of NF-κB by RP.

Evaluation of Ammonia Nitrogen Exposure in Immune Defenses Present on Spleen and Head-Kidney of Wuchang Bream (Megalobrama amblycephala)

Ammonia is one of the most important environmental factors in aquatic ecosystems. However, there are limited studies on the effects of chronic or long-term ammonia stress and its potential molecular mechanism in fish. This study aimed to investigate the immune response and molecular mechanisms in the spleen and head-kidney of fish following chronic ammonia exposure. Megalobrama amblycephala (9.98 ± 0.48 g) were exposed to different concentrations of total ammonia nitrogen (0-30 mg/L) for 30 days. Ammonia exposure caused significant increases in cortisol levels and decreases in lysozyme and complement 3/4 concentrations in the serum, indicating inhibitory effects of ammonia stress on innate immune responses. Ammonia exposure also induced concentration-dependent increases in ammonia concentrations in tissue, pathological damage and indexes of spleen and head-kidney. Additionally, the contents of immunoglobulin M (IgM), interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) as well as mRNA levels of toll-like receptors (TLRs)/Myeloid differentiation factor 88 (MyD88)-independent signaling molecules in the spleen and head-kidney were significantly downregulated after ammonia exposure. Our findings suggested that chronic ammonia exposure caused the suppression of innate and adaptive immune responses through downregulating TLR/MyD88-independent signaling. Adverse influences of chronic ammonia stress were more severe in the spleen than in the head-kidney.

Study of hepatoprotective effect of bearberry leaves extract under insulin resistance in rats

The aim of our study was to evaluate the antidiabetic and hepatoprotective efficacy of dry extract from bearberry leaves enriched with arginine in dexamethasone induced IR. Materials and methods. IR was induced in rats by low dose intraperitoneally injections of dexamethasone. Dexamethasone-induced IR in rats was treated by bearberry leaves extract enriched with arginine. Thus, animals were randomized into several groups including intact animals and animals, which administered reference compounds and medications. The activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamine transferase (GGT) were determined in blood serum and liver homogenate, in addition, in blood serum we measured lactate dehydrogenase (LDH) activity and lactate level and glycogen content liver tissue. Also, for the purpose of our experiment, in liver tissue were determined: thiobarbituric acid reactive substances (TBARS), diene conjugates (DC), and reduced glutathione (GSH) content; and superoxide dismutase (SOD), glutathione peroxidase (Gpx), and catalase (CAT) activities. All indices were determined using generally accepted unified methods or commercially available kits. Results. Long-term dexamethasone administration led to an increase in AST, ALT and GGT overall activity in the liver homogenate and serum; this could be the result of increased permeability of hepatocyte plasma membranes, as well as their enhanced synthesis in the liver. Studied extract ameliorate these indices of liver injury. Evaluation of indices that reflected oxidative stress and the antioxidant system status in liver confirmed oxidative stress development in IR rats` liver. Administration of arginine enriched bearberry leaves extract decrease TBARS and DC content in liver tissue, at the same time, improve SOD, Gpx, and CAT activities and increase GSH content. Conclusions. Bearberry leaves dry extract enriched with arginine inhibit oxidative stress development, improve membrane integrity, and normalize some indices of carbohydrate metabolism, particularly glycogen content in liver and lactate level in blood.

Arginine metabolism and its functions in growth, nutrient utilization, and immunonutrition of fish

Fish have limited ability in endogenous biosynthesis of arginine. Arginine is an indispensable amino acid for fish, and the arginine requirement varies with fish species and fish size. Recent studies on fish have demonstrated that arginine influences nutrient metabolism, stimulates insulin release, is involved in nonspecific immune responses and antioxidant responses, and elevates disease resistance. Specifically, arginine can regulate energy homeostasis via modulating the adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway, and also regulate protein synthesis via activating the target of rapamycin (TOR) signaling pathway. The present article reviews pertinent knowledge of arginine in fish, including dietary quantitative requirements, endogenous anabolism and catabolism, regulation of the endocrine and metabolic systems, and immune-regulatory functions under pathogenic challenge. Our findings showed that further data about the distribution of arginine after intake into specific cells, its sub-cellular sensor to initiate downstream signaling pathways, and its effects on fish mucosal immunity, especially the adaptive immune response against pathogenic infection in different species, are urgently needed.

N-carbamoylglutamate improves lipid metabolism, inflammation, and apoptosis responses in visceral adipocytes of Japanese seabass (Lateolabrax japonicus), in vivo and in vitro

This study applied in vivo and in vitro methods to investigate the effect of dietary N-carbamoylglutamate (NCG) on lipid metabolism, inflammation and apoptosis related-gene expression in visceral adipose tissue and isolated adipocytes of Japanese seabass (Lateolabrax japonicus). A basal diet and a test diet supplemented with 720 mg/kg NCG were fed to the fish for 10 weeks. During the growth trial, no mortality and no significant differences in growth performance were observed in fish between the 2 groups (P > 0.05). Plasma Arg content and mRNA level of argininosuccinate synthetase (ASS) in adipose tissue were significantly increased, which indicated that NCG inclusion promoted endogenous Arg synthesis. Thereafter, the potential effects of NCG treatment on lipid metabolism-related genes expression were studied through in vivo and in vitro methods. In the present study, we successfully established a primary adipocytes culture system and isolated pre-adipocytes in vitro of Japanese seabass for the first time. Both the results in vivo and in vitro showed that NCG treatment decreased the mRNA levels of genes related to adipogenesis (fatty acid synthase, FASN), cholesterol synthesis (3-hydroxy-3-methylglutaryl-CoA reductase, HMGCR) and fat deposition (lipoprotein lipase [LPL] and leptin), which revealed the underlying mechanism of NCG on reducing fat deposition. The results of this study demonstrated that NCG inclusion reduced the expression of inflammatory and apoptosis cytokines markedly in vivo and in vitro. In conclusion, NCG did exert beneficial effects on ameliorating adipogenesis, inflammation and apoptosis via promoting Arg endogenous synthesis in Japanese seabass.

Tributyrin Plays an Important Role in Regulating the Growth and Health Status of Juvenile Blunt Snout Bream (Megalobrama amblycephala), as Evidenced by Pathological Examination

The present study aimed to assess the role of tributyrin (TB) in regulating the growth and health status of juvenile blunt snout bream (Megalobrama amblycephala) through an 8-week feeding experiment. Six groups were fed experimental diets with added TB percentages of 0% (control group), 0.03%, 0.06%, 0.09%, 0.12% and 0.15%. The present results showed that TB supplementation in feed had some positive impacts on FW, WG, FCR and SGR, and the best results were found in the 0.06% TB group (P<0.05). However, TB supplementation in feed had no significant effects on SR, CF, VSI or whole-body composition (P>0.05). TB supplementation in feed increased antioxidant capacity and immunological capacity and attenuated the inflammatory response by increasing the activity of T-SOD, GPx, CAT and the levels of anti-inflammatory cytokines (IL-10 and TGF-β) and decreasing the levels of MDA and anti-inflammatory cytokines (TNF-α) (P<0.05). Furthermore, TB supplementation improved immunity by increasing the levels of immunoglobulins (IgM and IgG), C3 and IFN-γ (P<0.05). Surprisingly, 0.06%-0.12% TB supplementation significantly increased the content of IL-1β (P<0.05). However, TB supplementation in feed had no significant effects on the plasma content of GSH, HSP70, IL-8 and the activity of T-AOC (P>0.05). The possible mechanism was that TB activated PI3K/Akt/Nrf2 and inhibits the NF-κB signaling pathway, further regulating the mRNA levels of key genes with antioxidant capacity and the inflammatory response; for example, it increased the mRNA levels of Nrf2, Cu/Zn-SOD, HO-1, CAT, Akt, PI3K, GPx, IL-10, and TGF-β and decreased the mRNA levels of NF-κB and TNF-α (P<0.05). In addition, 0.06%-0.15% TB supplementation significantly increased the mRNA levels of IL-1β (P<0.05). TB supplementation in feed had no significant effects on the mRNA levels of HSP70, Mn-SOD and IL-8 (P>0.05). Evidence was presented that TB supplementation decreased the mortality rate caused by Aeromonas hydrophila challenge. In pathological examination, TB supplementation prevented hepatic and intestinal damage. Generally, TB supplementation improved the growth performance of juvenile blunt snout bream. Furthermore, TB supplementation activated PI3K/Akt/Nrf2 and inhibited the NF-κB signaling pathway, regulating health status and preventing hepatic and intestinal damage.

Fish infections associated with the genus Aeromonas: a review of the effects on oxidative status

The aim of this review was to summarize the current knowledge regarding the effects of aeromonosis on fish oxidative status. The bibliographic survey was carried out on the research platforms: Scopus and Science Direct. The keywords 'Aeromonas', 'fish' and 'oxidative status' (or 'oxidative stress', 'oxidative damage' and similar terms) were used. Scientific papers and short communications were considered. Studies involving fish aeromonosis and enzymatic or non-enzymatic markers of oxidative status were selected. The results of antioxidant enzymes activities/expressions after infection lack consistency, suggesting that these findings should be interpreted with caution. Most of the analysed studies pointed to an increase in reactive oxygen species, malondialdehyde and protein carbonylation levels, indicating possible oxidative damage caused by the infection. Thus, these three biomarkers are excellent indicators of oxidative stress during infection. Regarding respiratory burst activity, several studies have indicated increased activity, but other studies have indicated unchanged activity after infection. Nitric oxide levels also increased after infection in most studies. Therefore, it is suggested that the fish's immune system tries to fight a bacterial infection by releasing reactive oxygen and nitrogen species.

Amino Acids in Cell Signaling: Regulation and Function

Amino acids are the main building blocks for life. Aside from their roles in composing proteins, functional amino acids and their metabolites play regulatory roles in key metabolic cascades, gene expressions, and cell-to-cell communication via a variety of cell signaling pathways. These metabolic networks are necessary for maintenance, growth, reproduction, and immunity in humans and animals. These amino acids include, but are not limited to, arginine, glutamine, glutamate, glycine, leucine, proline, and tryptophan. We will discuss these functional amino acids in cell signaling pathways in mammals with a particular emphasis on mTORC1, AMPK, and MAPK pathways for protein synthesis, nutrient sensing, and anti-inflammatory responses, as well as cell survival, growth, and development.

Effects of dietary leucine levels on intestinal antioxidant status and immune response for juvenile golden pompano (Trachinotus ovatus) involved in Nrf2 and NF-κB signaling pathway

The aim of the study was to evaluate the effects of dietary leucine level on growth performance, intestinal antioxidant status and immune response involved in Nrf2 and NF-κB signaling pathway in juvenile golden pompano (Trachinotus ovatus). A total of 450 juvenile golden pompano (9.15 ± 0.04 g) were fed three isonitrogenous diets with graded leucine levels [1.25% (control), 2.77% and 5.84%] for 8 weeks. The results showed that, compared with the control group, the WG was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05), and the 5.84% dietary leucine group had a tendency to increase. Compared to control group, 5.84% dietary leucine group significantly decreased the moisture and ash contents of whole body (P < 0.05), meanwhile, 2.77% dietary leucine group significantly decreased moisture content of whole body, but significantly improved the whole body crude lipid content (P < 0.05). Compared with the control group, the ALP level was significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). Inversely, the AST and ALT activities were significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). Compared with the control group, GPx, T-AOC, SOD activities in group of 2.77% dietary arginine level were significantly increased (P < 0.05). However, MDA level showed a reverse trend, which was significantly decreased in fish fed with 2.77% dietary leucine level (P < 0.05). 2.77% dietary leucine levels significantly increased the relative expressions of Nrf2, HO-1, Cu/Zn-SOD, Mn-SOD and CAT (P < 0.05). In contrast, the relative expression of Keap1 showed a converse trend. Compared with the control group, the relative expressions of NF-κB, TNF-α and IL1-β were significantly lowered in fish fed with 2.77% of dietary leucine (P < 0.05). Additionally, 2.77% dietary leucine level significantly improved the relative expressions of TGF-β and IL-10 (P < 0.05). The 2.77% dietary leucine level significantly increased the muscular thickness compared with 5.84% dietary leucine level (P < 0.05). Furthermore, compared with the control group, the villus height and goblet cell counts were significantly improved in fish fed with 2.77% of dietary leucine (P < 0.05). These results indicated that the optimum dietary leucine plays an important role in promoting growth, enhancing antioxidant and immunity to maintain the intestinal health status of juvenile golden pompano.

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.

Protective effects of dietary arginine against oxidative damage and hepatopancreas immune responses induced by T-2 toxin in Chinese mitten crab (Eriocheir sinensis)

T-2 toxin is a secondary metabolite produced by Fusarium spp. that is a major cereal and animal feed contaminant. T-2 toxin has numerous adverse effects on animals, including hepatotoxicity. Arginine (Arg) is closely associated with the regulation of immune responses and antioxidant activity in tissues. The objective of the present study was to evaluate the protective effects of dietary Arg against oxidative damage and immune responses of the hepatopancreas induced by T-2 toxin in Chinese mitten crab. According to the results, 3.17% Arg in the diet decreased alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase activity in the haemolymph significantly, when compared with the levels of activity in the T-2 toxin group. Arg supplementation also increased superoxide dismutase and glutathione peroxidase activity, while decreasing malondialdehyde concentrations in the hepatopancreas, when compared with the levels in the T-2 toxin group. In addition, 3.17% Arg in the diet increased acid phosphatase and alkaline phosphatase activity in the hepatopancreas, as well as albumin concentrations in the haemolymph, when compared with the T-2 toxin group. Dietary Arg also regulated the expression of antioxidant enzyme-related genes (mitochondrial manganese superoxide dismutase, cytosolic manganese superoxide dismutase, and catalase) and immune related genes (prophenoloxidase, NF-κB-like transcription factor Relish, and lipopolysaccharide-induced TNF-α factor) to alleviate the damage associated with the T-2 toxin. Furthermore, Arg ameliorated damage to the hepatopancreas microstructure in the crabs. The results of the present study indicate that dietary Arg could enhance the antioxidant and immune capacity of Chinese mitten crab against oxidative damage and immune injury to the hepatopancreas induced by T-2 toxin.

Arginine supplementation improves growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, Eriocheir sinensis

To investigate the effects of arginine (Arg) on the growth, antioxidant capacity, immunity and disease resistance of juvenile Chinese mitten crab, three diets containing Arg levels at 1.72% (control), 2.73% and 3.72% were formulated and fed to Chinese mitten crab (0.22 ± 0.03 g) for eight weeks. The weight gain, ecdysterone and growth hormone in the serum, relative expression of insulin-like growth factor 2 in the hepatopancreas significantly increased in crabs fed the 2.73% and 3.72% Arg diets. The protein and lipid contents significantly increased in crabs fed the 3.72% Arg diet. The feed conversion ratios in crabs fed the diets with Arg additions were lower than in the control. Arg supplementation also enhanced the antioxidative capacity by increasing the activities of superoxide dismutase, catalase and the relative expression of Kelch-like ECH-associated protein 1 gene in the hepatopancreas, which subsequently decreased malondialdehyde content in the hepatopancreas. Besides, Arg also decreased nitric oxide content in the serum and the activity of nitric oxide synthetase in the hepatopancreas. The relative mRNA levels of crustin, relish, lysozyme and cryptocyanin genes were significantly upregulated by Arg supplementation. The activities of acid phosphatase and alkaline phosphatase in the serum significantly increased in crabs fed the 3.72% Arg diet than those in the control. Similarly, the relative mRNA levels of crustin, cryptocyanin and proPO genes were significantly upregulated in crabs fed the 2.73% Arg diet after lipopolysaccharide challenge, and in crabs fed the 3.72% Arg diet after the Poly (I:C) challenge. The crabs fed the 2.73% and 3.72% Arg diets had higher survival rate after bacterial infection than those fed the control diet. This study indicates that the addition of Arg to the diet at 2.7-3.7% can improve the growth, survival, antioxidant capacity, immunity and disease resistance in juvenile Chinese mitten crab.

Dietary N-Carbamylglutamate (NCG) alleviates liver metabolic disease and hepatocyte apoptosis by suppressing ERK1/2-mTOR-S6K1 signal pathway via promoting endogenous arginine synthesis in Japanese seabass (Lateolabrax japonicus)

N-Carbamylglutamate (NCG), an analogue of N-acetylglutamate (NAG), can promote the synthesis of endogenous Arginine (Arg) in mammals, but not well studied in fish. This study was conducted to investigate the capacity of Arg endogenous synthesis by NCG, and the effects of various dietary NCG doses on growth performance, hepatic health and underlying nutrient regulation metabolism on ERK1/2-mTOR-S6K1 signaling pathway in Japanese seabass (Lateolabrax japonicus). Four experimental diets were prepared with NCG supplement levels of 0 (N0), 360 (N360), 720 (N720) and 3600 (N3600) mg/kg, in which N360 was at the maximum recommended level authorized by MOA, China in fish feed, and the N720 and N3600 levels were 2 and 10-fold of N360, respectively. Each diet was fed to 6 replicates with 30 Japanese seabass (initial body weight, IBW = 11.67 ± 0.02 g) in each tank. The results showed that the dietary NCG supplementation had no significant effects on the SGR and morphometric parameters of Japanese seabass, but 360-720 mg/kg NCG inclusion promoted PPV, while the 10-fold (3600 mg/kg) overdose of NCG had remarkably negative effects with significantly reduced feed efficiency, PPV and LPV. We found that Japanese seabass can utilize 360-720 mg/kg NCG to synthesis Arg to improve the amino acid metabolism by increasing plasma Arg and up-regulating intestinal ASL gene expression. Increased plasma GST and decreased MDA indicated the improved antioxidant response. Dietary NCG inclusion decreased plasma IgM and down-regulated the mRNA levels of inflammation (TNF-α and IL8), apoptosis (caspase family) and fibrosis (TGF-β1) related genes in the liver. The immunofluorescence examination revealed significantly decreased hepatic apoptosis and necrosis signals in the NCG groups. The ameliorated liver function and histological structure were closely related to the improved lipid metabolism parameters with decreased plasma VLDL and hepatic TG and NEFA accumulation, down-regulated fatty acid and cholesterol synthesis and simultaneously increased lipolysis gene mRNA levels, which regulated by inhibiting phosphorylation of ERK1/2-mTOR-S6K1 signaling pathway. Consuming 3600 mg/kg of dietary NCG is not safe for Japanese seabass culturing with the significantly increased FCR and decreased protein and lipid retention, and reduced plasma ALB. Accordingly, the observed efficacy and safety level of dietary NCG in the diet of Japanese seabass is 720 mg/kg.

Effects of dietary blackberry syrup supplement on growth performance, antioxidant, and immunological responses, and resistance of Nile tilapia, Oreochromis niloticus to Plesiomonas shigelloides

The present study investigated the effects of dietary blackberry syrup on growth performance, haematological, non-specific immune and spleen gene expression responses of Nile tilapia, Oreochromis niloticus. Five experimental groups of fish with mean weights of 26.75 ± 2.67 g were used in the study; three of them were fed with blackberry syrup incorporated diets (7.5 g kg^-1- BBRY7.5, 15 g kg^-1- BBRY15, 30 g kg^-1- BBRY30), whereas an additive free basal diet served as the control. Additionally, the fifth group was an antibiotic medicated diet (0.02 g kg^-1- ABTC), prepared with the florfenicol. Dietary blackberry syrup especially at 15 g kg^-1 significantly increased growth performance, respiratory burst activity, potential killing activity, phagocytic activity, phagocytic index, lysozyme activity, myeloperoxidase activity, total immunoglobulin levels, serum SOD activity and serum CAT activity (p < 0.05). Furthermore, dietary blackberry syrup increased the expression levels of immune [heat shock protein 70 (HSP70), interleukin 1, beta (IL-1β), tumor necrosis factor (TNF-α), interferon gamma (IFN-γ), immunoglobulin M (IgM)] and antioxidant [glutathione peroxidase (GPx)] related genes in the spleen of fish fed with especially 15 g kg^-1 blackberry syrup (p < 0.05). At the end of the 20-day challenge period the survival rates were significantly higher in the BBRY15 and ABTC groups compared to all other treatment groups (p < 0.05). As a result, feeding Nile tilapia with a diet containing 15 g kg^-1 blackberry syrup over a period of 90 days might be adequate to improve growth performance, fish immune parameters, antioxidant status, as well as survival rate against P. shigelloides, similar to antibiotic treatment. Hence, blackberry syrup can be used as an antibiotics replacer for controlling P. shigelloides in tilapia feed.

Effect of N-carbamoylglutamate supplementation on the growth performance, antioxidant status and immune response of mirror carp (Cyprinus carpio) fed an arginine-deficient diet

The present study was conducted to determine the effect of dietary N-carbamoylglutamate (NCG) supplementation on the growth performance, antioxidant capability and immune responses of mirror carp (Cyprinus carpio) fed an arginine (Arg)-deficient diet. A total of 630 mirror carp (41.65 ± 0.14 g) were fed diets (Arg 1.24% of the diet) that were supplemented with 0.50% Arg (control diet) or graded levels of NCG at 0 (Arg deficiency diet), 0.04%, 0.08%, 0.12%, 0.16% and 0.20% for 8 weeks. The results showed that, compared with the control diet, the Arg-deficient diet supplementation with 0 NCG (1) decreased the final body weight (FWB), the weight gain rate (WGR) or the protein efficiency ratio (PER) and increased the feed conversion ratio (FCR); (2) decreased the concentration of Arg and nitric oxide (NO) and the activity of total nitric oxide synthetase (T-NOS) in the plasma; (3) decreased the activities of superoxide dismutase (SOD) in the proximal intestine (PI), catalase (CAT) in the PI and distal intestine (DI), and glutathione peroxidase (GPx) in PI and mid-intestine (MI) and increased the concentration of malondialdehyde (MDA) in the PI, MI and DI; and (4) decreased the activity of lysozyme in the plasma, increased the relative mRNA expression of tumor necrosis factor-α (TNF-α), interleukin1β (IL-1β) and interleukin 8 (IL-8) in the PI, MI and DI, and decreased the relative mRNA expression of interleukin 10 (IL-10) in the PI and MI, and transforming growth factor β2 (TGF-β2) in the PI, MI and DI. Compared with the Arg deficient-diet supplementation with 0 NCG, (1) 0.12% or 0.16% NCG increased the FBW, WGR and PER, and 0.16% NCG increased the FCR; (2) 0.08%-0.20% NCG increased the concentration of Arg, NO and the activity of T-NOS; (3) 0.08% NCG increased the activities of SOD in the PI and MI, and 0.12% NCG increased activities of CAT and GPx in the PI, MI and DI; and (4) 0.04%-0.20% NCG increased the activity of lysozyme, 0.04%-0.20% NCG decreased the relative mRNA expression of TNF-α, IL-1β and IL-8 in the PI and MI, and 0.04%-0.20% NCG increased the relative mRNA expression of IL-10 and TGF-β2 in the PI and MI. The present results indicated that dietary 0.12% or 0.16% NCG improved the growth performance, feed utilization, intestinal antioxidant capacity and immune response of mirror carp fed an Arg-deficient diet.

Effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream, Megalobrama amblycephala

The present study assessed the effects of dietary arginine on intestinal antioxidant status and immunity involved in Nrf2 and NF-κB signaling pathway in juvenile blunt snout bream. Fish were fed three practical diets with graded arginine levels (0.87%, 1.62% and 2.70%) for 8 weeks. Compared with the control group (0.87%), the counts of white blood cell (WBC), red blood cell (RBC) and hemoglobin (HGB) content were significantly improved at dietary arginine levels of 1.62% (P<0.05). Plasma albumin (ALB) levels and alkaline phosphatase (ALP) activities were significantly improved at dietary arginine levels of 1.62% and 2.70% (P < 0.05). Alanine transaminase (ALT) activity was decreased in fish fed with 1.62% dietary arginine level (P<0.05). Plasma glutathione peroxidase (GPx) activities, copper-zinc superoxide dismutase (Cu/Zn-SOD) activities, total antioxidant capacity (T-AOC) activities and glutathione (GSH) levels were significantly increased at dietary arginine levels of 1.62% and 2.70% (P<0.05). Plasma total superoxide dismutase (T-SOD) activities and catalase (CAT) activities were significantly improved in fish fed with 1.62% dietary arginine level. Significantly higher manganese superoxide dismutase (Mn-SOD) activity was observed in fish fed with 1.62% dietary arginine level compared with 2.70% dietary arginine level (P<0.05). 1.62% and 2.70% dietary arginine levels significantly lowered malondialdehyde (MDA) levels. The relative expression of nuclear factor erythroid 2-related factor 2 (Nrf2) was significantly increased in fish fed with 1.62% dietary arginine level, inversely, the relative expression of Kelch-like ECH-associated protein 1 (Keap1) showed a converse trend. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of Cu/Zn-SOD, GPx and CAT. Furthermore, 2.70% dietary arginine level significantly lowered the relative expression of Mn-SOD compared with the control group and 1.62% dietary arginine levels. The relative expressions of Interleukin 1β (IL-1β), tumour necrosis factor-α (TNF-α) and nuclear factor-kappa B (NF-κB) were lowered in fish fed with 1.62% dietary arginine level. 1.62% and 2.70% dietary arginine levels significantly improved the relative expressions of transforming growth factor-β (TGF-β). Hematocrit (HCT), aspartate aminotransferase (AST) activities, interleukin 8 (IL-8) and interleukin 10 (IL-10) expressions were not significantly affected by the graded dietary arginine levels. These results suggest that the optimal dietary arginine level plays an important role in enhancing antioxidant and immune status to maintain the intestinal health of juvenile blunt snout bream.