Oxidative damage repair by glutamine in fish enterocytes

Effects of early-life amino acids supplementation on fish responses to a thermal challenge

Nutritional programming is a promising concept for promoting metabolic adaptation of fish to challenging conditions, such as the increase in water temperature. The present work evaluates in ovo arginine or glutamine supplementation as enhancers of zebrafish metabolic or absorptive capacity, respectively, at optimum (28 ºC) and challenging temperatures (32 ºC) in the long-term. Growth performance, free amino acids profile, methylation index and the activity levels of digestive and intermediary metabolism enzymes were analysed to assess the metabolic plasticity induced by an early nutritional intervention. Temperature affected fish larvae growth performance. At the end of the experimental period 28 ºC-fish showed higher dry weight than 32 ºC-fish. The effects of the early supplementation were reflected in the larval free amino acids profile at the end of the experiment. Higher methylation potential was observed in the ARG-fish. In ovo amino acid supplementation modulated the metabolic response in zebrafish larvae, however, the magnitude of this effect differed according to the amino acid and the temperature. Overall, arginine supplementation enhanced carbohydrates metabolism at 32 ºC. In conclusion, the present work suggests that in ovo arginine supplementation may promote a better adaptive response to higher temperatures.

Exposure to pollutants present in Iguaçu River Southern Brazil affect the health of Oreochromis niloticus (Linnaeus, 1758): Assessment histological, genotoxic and biochemical

Urban sewage is a source of major contamination in aquatic systems and contributes to environmental and human health disturbances. This study investigates the effects of sewage-polluted waters from Iguaçu River on the health of juvenile Oreochromis niloticus. Two hundred four specimens were exposed to riverine water in four groups: no diluted, 25 and 50 % diluted water and a control group without tested water for 72 days. Biological samples were obtained for histopathological, neurotoxicity, antioxidant defenses, genotoxicity, metallothionines expression and polycyclic aromatic hydrocarbons (PAHs) metabolites. The results showed histopathological alterations in liver and gills, genotoxic alteration in erythrocytes, reduction of acetylcholinesterase activity in brain and muscle, activation of antioxidant defenses in the liver, recruitment of metals by metallothionein and the detection of PAHs metabolites in bile. These results demonstrate that juveniles of O. niloticus are susceptible to Iguaçu River exposure water and they can be used as indicator of water quality.

Nutrition and Functions of Amino Acids in Fish

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve the growth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Supplementation of enzyme-treated soy protein saves dietary protein and promotes digestive and absorptive ability referring to TOR signaling in juvenile fish

This study was conducted to evaluate the effect of enzyme-treated soy protein (ETSP) supplementation in the low-protein diet on growth performance, digestive and absorptive capacities, and related signaling molecules' gene expressions in juvenile Jian carp. The results showed that percent weight gain (PWG), specific growth rate (SGR), and feed intake (FI) were decreased by reducing dietary protein from 34 to 32% (P < 0.05). Supplying low-protein diet with optimal ETSP increased previously mentioned indices of juvenile Jian carp (P < 0.05), which also had no significant difference with the high-protein diet (34%CP) (P > 0.05). Compared with the low-protein diet, appropriate ETSP supplementation in the low-protein diet increased (P < 0.05) (1) the trypsin, lipase, and amylase activities in the hepatopancreas; (2) cholecystokinin concentration in the proximal intestine; (3) the γ-glutamyl transpeptidase (γ-GT), alkaline phosphatase (AKP), and Na⁺/K⁺-ATPase activities in all intestinal segments; and (4) the messenger RNA (mRNA) levels of trypsin, lipase, and amylase in hepatopancreas and γ-GT in the mid (MI) and distal (DI) intestine, alkaline phosphatase in MI, and Na⁺/K⁺-ATPase and target of rapamycin in all intestinal segments. At the same time, appropriate ETSP supplementation in the low-protein diet downregulated the mRNA levels of AKP in the DI and eIF4E-binding protein 2 in all intestinal segments (P < 0.05). In conclusion, adding 10 g ETSP/kg diet in the low-protein diet can restore the growth performance and digestive and absorptive abilities to the levels in group with 34% dietary protein. Supplementation of optimal ETSP in the low-protein diet enhanced the digestive and absorptive abilities and regulated the signaling molecules related to the TOR signaling pathway.

Preventive and reparative effects of isoleucine against copper-induced oxidative damage in primary fish enterocytes

The present study aimed to assess the possible preventive and reparative effects of isoleucine (Ile) against copper (Cu)-induced oxidative stress in fish enterocytes in vitro. In experiment 1, enterocytes were preincubated with increasing concentrations of Ile (0, 50, 120, 190, 260, and 330 mg L^-1) for 72 h followed by exposure to 6 mg L^-1 Cu for 24 h. In experiment 2, the enterocytes were pretreated with 6 mg L^-1 Cu for 24 h and then treated with 0-330 mg L^-1 Ile for 72 h to investigate its potential reparative role. The results of experiment 1 showed that Cu exposure increased lactate dehydrogenase (LDH) activity and malondialdehyde and protein carbonyl (PC) content; these changes were completely suppressed by pretreatment with Ile at optimum concentrations (P < 0.05). Moreover, Ile pretreatment prevented the decrease in superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in the enterocytes exposed to Cu (P < 0.05). Additionally, cells exposed to Cu exhibited adaptive increases in glutathione-S-transferase (GST) activity. In experiment 2, the LDH activity and protein oxidation induced by Cu were completely reversed by Ile posttreatment. Meanwhile, the Cu-induced decrease in SOD, GPx, and GST activity was completely reversed by subsequent Ile treatment, but the reduced glutathione content was not restored. Collectively, these results indicate that Ile suppresses Cu-induced oxidative damage via preventive and reparative pathways in primary enterocytes and thus protects the structural integrity of enterocytes in fish.

Effects of Ala-Gln feeding strategies on growth, metabolism, and crowding stress resistance of juvenile Cyprinus carpio var. Jian

The present study was conducted to evaluate the effects of different L-alanyl-l-glutamine (Ala-Gln) feeding strategies on the growth performance, metabolism and crowding stress resistance related parameters in juvenile Jian carp (Cyprinus carpio var. Jian) under crowded condition (80 g/L). Juvenile Jian carp (initial weight 26.1 ± 0.6 g) were distributed into five groups which fed with graded concentrations (0% or 1.0%) of Ala-Gln for eight weeks. Control group (I, 0/0) fed with control diet (0% Ala-Gln) throughout the feeding trial. The other four groups employed different control and experimental diet feeding strategies ranging from two weeks control diet fed and two weeks experimental diet (1% Ala-Gln) fed (II, 0/2) to eight weeks experimental diet fed (V, 4/4). Results revealed that Mean weight gain (MEG) under all different feeding strategies of Ala-Gln were significantly higher than that of the control group (p < 0.05), and MEG of group II (201.90%) was even higher than that of group IV (184.70%). Liver glycogen and blood total protein of groups II, III and V were significantly higher than that in groups I and IV (p < 0.05). The highest level of serum thyroxine (10.07 ng/ml), insulin-like growth factor-I (52.40 ng/ml) and insulin (9.73 μ IU/mL) were observed in group V. However, diet supplemented with Ala-Gln did not affect the levels of serum glucose, cortisol and catecholamine in fish. The mRNA expression of GR1a, GR1b and GR2 were also significantly changed in Ala-Gln supplementation groups compared with control group (p < 0.05). After fish intraperitoneally injected with virulent Aeromonas hydrophila, the fish survival rates were significantly increased in all Ala-Gln supplementation groups compared with control group (p < 0.05). Results from the present experiment showed the importance of dietary supplementation of Ala-Gln in benefaction of the growth performance, metabolism and crowding stress resistance in Jian carp breeding. The optimal feeding strategy was alternatively fed with control diet and then experimental diet at an interval of two weeks for juvenile Jian carp under crowded condition.

Soyabean glycinin depresses intestinal growth and function in juvenile Jian carp (Cyprinus carpio var Jian): protective effects of glutamine

This study investigated the effects of glycinin on the growth, intestinal oxidative status, tight junction components, cytokines and apoptosis signalling factors of fish. The results showed that an 80 g/kg diet of glycinin exposure for 42 d caused poor growth performance and depressed intestinal growth and function of juvenile Jian carp (Cyprinus carpio var. Jian). Meanwhile, dietary glycinin exposure induced increases in lipid peroxidation and protein oxidation; it caused reductions in superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx) activities; and it increased MnSOD, CuZnSOD, GPx1b and GPx4a mRNA levels, suggesting an adaptive mechanism against stress in the intestines of fish. However, dietary glycinin exposure decreased both the activity and mRNA levels of nine isoforms of glutathione-S-transferase (GST) (α, μ, π, ρ, θ, κ, mGST1, mGST2 and mGST3), indicating toxicity to this enzyme activity and corresponding isoform gene expressions. In addition, glycinin exposure caused partial disruption of intestinal cell-cell tight junction components, disturbances of cytokines and induced apoptosis signalling in the distal intestines>mid intestines>proximal intestines of fish. Glycinin exposure also disturbed the mRNA levels of intestinal-related signalling factors Nrf2, Keap1a, Keap1b, eleven isoforms of protein kinase C and target of rapamycin/4E-BP. Interestingly, glutamine was observed to partially block those negative influences. In conclusion, this study indicates that dietary glycinin exposure causes intestinal oxidative damage and disruption of intestinal physical barriers and functions and reduces fish growth, but glutamine can reverse those negative effects in fish. This study provides some information on the mechanism of glycinin-induced negative effects.

Dietary glutamine supplementation effects on amino acid metabolism, intestinal nutrient absorption capacity and antioxidant response of gilthead sea bream (Sparus aurata) juveniles

A study was undertaken to evaluate dietary glutamine supplementation effects on gilthead sea bream performance, intestinal nutrient absorption capacity, hepatic and intestinal glutamine metabolism and oxidative status. For that purpose gilthead sea bream juveniles (mean weight 13.0g) were fed four isolipidic (18% lipid) and isonitrogenous (43% protein) diets supplemented with 0, 0.5, 1 and 2% glutamine for 6weeks. Fish performance, body composition and intestinal nutrient absorption capacity were not affected by dietary glutamine levels. Hepatic and intestinal glutaminase (GlNase), glutamine synthetase (GSase), alanine aminotransferase, aspartate aminotransferase and glutamate dehydrogenase activities were also unaffected by dietary glutamine supplementation. In the intestine GlNase activity was higher and GSase/GlNase ratio was two-fold lower than in the liver, suggesting a higher use of glutamine for energy production by the intestine than by the liver. The liver showed higher catalase and glucose-6-phosphate dehydrogenase activities, while the intestine presented higher glutathione peroxidase and glutathione reductase activities and oxidised glutathione content, which seems to reveal a higher glutathione dependency of the intestinal antioxidant response. Total and reduced glutathione contents in liver and intestine and superoxide dismutase activity in the intestine were enhanced by dietary glutamine, though lipid peroxidation values were not affected. Overall, differences between liver and intestine glutamine metabolism and antioxidant response were identified and the potential of dietary glutamine supplementation to gilthead sea bream's antioxidant response was elucidated.

Effect of dietary glutamine on growth performance, non-specific immunity, expression of cytokine genes, phosphorylation of target of rapamycin (TOR), and anti-oxidative system in spleen and head kidney of Jian carp (Cyprinus carpio var. Jian)

This study was designed to investigate the effects of dietary glutamine on the growth performance, cytokines, target of rapamycin (TOR), and antioxidant-related parameters in the spleen and head kidney of juvenile Jian carp (Cyprinus carpio var. Jian). Fish were fed the basal (control) and glutamine-supplemented (12.0 g glutamine kg(-1) diet) diets for 6 weeks. Results indicated that the dietary glutamine supplementation improved the growth performance, spleen protein content, serum complement 3 content, and lysozyme activity in fish. In the spleen, glutamine down-regulated the expression of the interleukin 1 and interleukin 10 genes, and increased the level of phosphorylation of TOR protein. In the head kidney, glutamine down-regulated the tumor necrosis factor α and interleukin 10 gene expressions, phosphorylated and total TOR protein levels, while up-regulated the transforming growth factor β2 gene expression. Furthermore, the protein carbonyl content was decreased in the spleen of fish fed glutamine-supplemented diet; conversely, the anti-hydroxyl radical capacity and glutathione content in the spleen were increased by glutamine. However, diet supplemented with glutamine did not affect the lipid peroxidation, anti-superoxide anion capacity, and antioxidant enzyme activities in the spleen. Moreover, all of these antioxidant parameters in the head kidney were not affected by glutamine. Results from the present experiment showed the importance of dietary supplementation of glutamine in benefaction of the growth performance and several components of the innate immune system, and the deferential role in cytokine gene expression, TOR kinase activity, and antioxidant status between the spleen and head kidney of juvenile Jian carp.