Dietary taurine modulates hepatic oxidative status, ER stress and inflammation in juvenile turbot (Scophthalmus maximus L.) fed high carbohydrate diets

Dietary sodium acetate and sodium butyrate attenuate intestinal damage and improve lipid metabolism in juvenile largemouth bass (Micropterus salmoides) fed a high carbohydrate diet by reducing endoplasmic reticulum stress

High-carbohydrate (HC) diets decrease the intestinal levels of sodium acetate (SA) and sodium butyrate (SB) and impair the gut health of largemouth bass; however, SA and SB have been shown to enhance immunity and improve intestinal health in farmed animals. Thus, the present study was to investigate the effects of dietary SA and SB on HC diet-induced intestinal injury and the potential mechanisms in juvenile largemouth bass. The experiment set five isonitrogenous and isolipidic diets, including a low-carbohydrate diet (9% starch) (LC), a high carbohydrate diet (18% starch) (HC), and the HC diet supplemented with 2 g/kg SA (HCSA), 2 g/kg SB (HCSB) or a combination of 1 g/kg SA and 1 g/kg SB (HCSASB). The feeding experiment was conducted for 8 weeks. A total of 525 juvenile largemouth bass with an initial body weight of 7.00 ± 0.20 g were used. The results showed that dietary SA and SB improved the weight gain rate and specific growth rate (P < 0.05) and ameliorated serum parameters (alkaline phosphatase, acid phosphatase, glutamate transaminase, and glutamic oxaloacetic transaminase) (P < 0.05). And, importantly, dietary SA and SB repaired the intestinal barrier by increasing the expression levels of zonula occludens-1, occludin, and claudin-7 (P < 0.05), reduced HC-induced intestinal damage, and alleviated intestinal inflammation and cell apoptosis by attenuating HC-induced intestinal endoplasmic reticulum stress (P < 0.05). Further results revealed that dietary SA and SB reduced HC-induced intestinal fat deposition by inhibiting adipogenesis and promoting lipolysis (P < 0.05). In summary, this study demonstrated that dietary SA and SB attenuated HC-induced intestinal damage and reduced excessive intestinal fat deposition in largemouth bass.

Identification and expression analysis of transcripts involved in taurine biosynthesis during early ontogeny of tropical gar Atractosteus tropicus

In fishes, the availability of taurine is regulated during ontogenetic development, where its endogenous synthesis capacity is species dependent. Thus, different pathways and involved enzymes have been described: pathway I (cysteine sulfinate-dependent pathway), cysteine dioxygenase type 1 (cdo1) and cysteine sulfinic acid decarboxylase (csad); pathway II (cysteic acid pathway), cdo1 and glutamic acid decarboxylase (gad); and pathway III (cysteamine pathway), 2-aminoethanethiol dioxygenase (ado); whereas taurine transporter (taut) is responsible for taurine entry into cells on the cell membrane and the mitochondria. This study determined if the tropical gar (Atractosteus tropicus), an ancient holostean fish model, has the molecular mechanism to synthesize taurine through the identification and analysis expression of transcripts coding for proteins involved in its biosynthesis and transportation, at different embryo-larvae stages and in different organs of juveniles (31 dah). We observed a fluctuating expression of all transcripts involved in the three pathways at all analyzed stages. All transcripts are expressed during the beginning of larval development; however, ado and taut show a peak expression at 9 dah, and all transcripts but csad decreased at 23 dah, when the organism ended the larval period. Furthermore, at 31 dah, we observed taut expression in all examined organs. The transcripts involved in pathways I and III are expressed differently across all organs, whereas pathway II was only observed in the brain, eye, and skin. The results suggested that taurine biosynthesis in tropical gar is regulated during its early development before first feeding, and the pathway might also be organ-type dependent.

Methionine: An Indispensable Amino Acid in Cellular Metabolism and Health of Atlantic Salmon

Methionine is an indispensable amino acid with an important role as the main methyl donor in cellular metabolism for both fish and mammals. Metabolization of methionine to the methyl donor S-adenosylmethionine (SAM) has consequence for polyamine, carnitine, phospholipid, and creatine synthesis as well as epigenetic modifications such as DNA- and histone tail methylation. Methionine can also be converted to cysteine and contributes as a precursor for taurine and glutathione synthesis. Moreover, methionine is the start codon for every protein being synthetized and thereby serves an important role in initiating translation. Modern salmon feed is dominated by plant ingredients containing less taurine, carnitine, and creatine than animal-based ingredients. This shift results in competition for SAM due to an increasing need to endogenously synthesize associated metabolites. The availability of methionine has profound implications for various metabolic pathways including allosteric regulation. This necessitates a higher nutritional need to meet the requirement as a methyl donor, surpassing the quantities for protein synthesis and growth. This comprehensive review provides an overview of the key metabolic pathways in which methionine plays a central role as methyl donor and unfolds the implications for methylation capacity, metabolism, and overall health particularly emphasizing the development of fatty liver, oxidation, and inflammation when methionine abundance is insufficient focusing on nutrition for Atlantic salmon (Salmo salar).

Dietary Betaine Attenuates High-Carbohydrate-Diet-Induced Oxidative Stress, Endoplasmic Reticulum Stress, and Apoptosis in Mandarin Fish (Siniperca chuatsi)

To investigate the impact of betaine on high-carbohydrate-diet-induced oxidative stress and endoplasmic reticulum (ER) stress, mandarin fish (Siniperca chuatsi) (23.73 ± 0.05 g) were fed with control (NC), betaine (BET), high carbohydrate (HC), and high carbohydrate + betaine (HC + BET) diets for 8 weeks. The results showed that betaine significantly promoted the growth of mandarin fish irrespective of the dietary carbohydrate levels. The HC diet induced oxidative stress, as evidenced by significantly elevated MDA levels. The HC diet significantly stimulated the mRNA levels of genes involved in ER stress (ire1, perk, atf6, xbp1, eif2α, atf4, chop), autophagy (ulk1, becn1, lc3b), and apoptosis (bax). However, betaine mitigated HC-diet-induced oxidative stress by modulating antioxidant enzymes and alleviated ER stress by regulating the mRNA of genes in the PERK-eIF2a-ATF4 pathway. Additionally, betaine significantly reduced the mRNA levels of becn1 and bax, along with the apoptosis rate, indicating a mitigating effect on autophagy and apoptosis. Overall, dietary betaine improved growth, attenuated HC-diet-induced oxidative stress and ER stress, and ultimately alleviated apoptosis in mandarin fish. These findings provide evidence for the use of betaine in aquafeeds to counter disruptive effects due to diets containing high carbohydrate levels.

Early Molecular Immune Responses of Turbot (Scophthalmus maximus L.) Following Infection with Aeromonas salmonicida subsp. salmonicida

Turbot aquaculture production is an important economic activity in several countries around the world; nonetheless, the incidence of diseases, such furunculosis, caused by the etiological agent A. salmonicida subsp. salmonicida, is responsible for important losses to this industry worldwide. Given this perspective, this study aimed to evaluate early immune responses in turbot (S. maximus L.) following infection with A. salmonicida subsp. salmonicida. For this, 72 fish were individually weighed and randomly distributed into 6 tanks in a circulating seawater system. For the bacterial challenge, half of the individuals (3 tanks with 36 individuals) were infected using a peritoneal injection with the bacterial suspension, while the other half of individuals were injected with PBS and kept as a control group. Several factors linked to the innate immune response were studied, including not only haematological (white blood cells, red blood cells, haematocrit, haemoglobin, mean corpuscular volume, mean cell haemoglobin, mean corpuscular haemoglobin concentration, neutrophils, monocytes, lymphocytes, thrombocytes) and oxidative stress parameters, but also the analyses of the expression of 13 key immune-related genes (tnf-α, il-1β, il-8, pparα-1, acox1, tgf-β1, nf-kB p65, srebp-1, il-10, c3, cpt1a, pcna, il-22). No significant differences were recorded in blood or innate humoral parameters (lysozyme, anti-protease, peroxidase) at the selected sampling points. There was neither any evidence of significant changes in the activity levels of the oxidative stress indicators (catalase, glutathione S-transferase, lipid peroxidation, superoxide dismutase). In contrast, pro-inflammatory (tnf-α, il-1β), anti-inflammatory (il-10), and innate immune-related genes (c3) were up-regulated, while another gene linked with the lipid metabolism (acox1) was down-regulated. The results showed new insights about early responses of turbot following infection with A. salmonicida subsp. salmonicida.

Dietary taurine supplementation counteracts deoxynivalenol-induced liver injury via alleviating oxidative stress, mitochondrial dysfunction, apoptosis, and inflammation in piglets

Deoxynivalenol (DON), as a widespread Fusarium mycotoxin in cereals, food products, and animal feed, is detrimental to both human and animal health. The liver is not only the primary organ responsible for DON metabolism but also the principal organ affected by DON toxicity. Taurine is well known to display various physiological and pharmacological functions due to its antioxidant and anti-inflammatory properties. However, the information regarding taurine supplementation counteracting DON-induced liver injury in piglets is still unclear. In our work, twenty-four weaned piglets were subjected to four groups for a 24-day period, including the BD group (a basal diet), the DON group (3 mg/kg DON-contaminated diet), the DON+LT group (3 mg/kg DON-contaminated diet + 0.3% taurine), and the DON+HT group (3 mg/kg DON-contaminated diet + 0.6% taurine). Our findings indicated that taurine supplementation improved growth performance and alleviated DON-induced liver injury, as evidenced by the reduced pathological and serum biochemical changes (ALT, AST, ALP, and LDH), especially in the group with the 0.3% taurine. Taurine could counteract hepatic oxidative stress in piglets exposed to DON, as it reduced ROS, 8-OHdG, and MDA concentrations and improved the activity of antioxidant enzymes. Concurrently, taurine was observed to upregulate the expression of key factors involved in mitochondrial function and the Nrf2 signaling pathway. Furthermore, taurine treatment effectively attenuated DON-induced hepatocyte apoptosis, as verified through the decreased proportion of TUNEL-positive cells and regulation of the mitochondria-mediated apoptosis pathway. Finally, the administration of taurine was able to reduce liver inflammation due to DON, by inactivating the NF-κB signaling pathway and declining the production of pro-inflammatory cytokines. In summary, our results implied that taurine effectively improved DON-induced liver injury. The underlying mechanism should be that taurine restored mitochondrial normal function and antagonized oxidative stress, thereby reducing apoptosis and inflammatory responses in the liver of weaned piglets.

Molecular characterization and immune functions of lipasin in Nile tilapia (Oreochromis niloticus): Involvement in the regulation of tumor necrosis factor-α secretion

Lipasin, the product of the angiopoietin-like 8 (angptl8) gene, is known as a critical regulator of plasma lipid metabolism. However, its immune function in vertebrates is currently poorly understood. By 5'/3'-rapid amplification of cDNA ends (RACE), we established the structural identity of Nile tilapia (Oreochromis niloticus) angptl8. The transcripts of tilapia angptl8 were widely expressed in various tissues, with the highest levels in the liver. Following lipopolysaccharide in vivo challenges, time-dependent angptl8 gene expression was observed in the head kidney and liver. On the basis of the sequence obtained, we produced recombinant lipasin that inhibited lipoprotein lipase activity. Treatment of head kidney leukocytes with lipasin stimulated tumor necrosis factor-α (TNF-α) secretion and gene expression. In addition, lipasin-induced TNF-α secretion could be prevented by inhibiting the nuclear factor-kappa B (NF-κB) signaling pathway. Furthermore, lipasin enhanced the phosphorylation and degradation of IκBα and promoted translocation of the p65 subunit of NF-κB to the nucleus. Collectively, the current findings suggested that lipasin was involved in the immune response of Nile tilapia and stimulated TNF-α secretion by activating the NF-κB pathway in tilapia head kidney leukocytes.

Effect of substitution of taurine for methionine and additional taurine supplementation on the performance and antioxidative capacity of laying hens

Taurine (TAU), a sulfur-containing amino acid that synthesized from methionine and cystine, plays vital roles in maintenance of redox balance. The effect of substitution of TAU for methionine was evaluated in vivo and in vitro. The effects of replacing methionine with TAU and additional TAU supplementation on the performance and antioxidant capacity of laying hens were evaluated. The in vitro cultured chicken primary hepatocytes and intestinal epithelial cells were further employed. Two hubdred eighty-eight 40-wk-old Isa brown laying hens were divided into 4 groups and subjected one to the following treatments: fed with basal diet with 0.17% crystallized DL-Met (CON), the control diet and replace 25% (21% total Met, 21TAU) or 50% (42% total Met, 42TAU) of crystallized DL-Met with taurine, the control diet supplemented with 0.1% taurine (0.1% TAU). The laying rate, feed intake, egg weight, and feed efficiency were not influenced (P > 0.05) by TAU replacement or additional TAU supplementation. In the liver, 0.1% TAU decreased SOD but increased GSH-Px activity (P < 0.01). In duodenum, 42TAU decreased SOD activity (P < 0.05) while 0.1% TAU decreased GSH level and SOD activity (P < 0.05). In the hepatocytes, TAU treatment decreased (P < 0.05) the MDA and GSH contents, whereas increased SOD and GSH-Px activities (P < 0.05). Meanwhile, TAU treatment decreased (P < 0.05) the protein expression of Nrf2 while increase Keap1 expression. The mRNA expression of Nrf2, SOD1, SOD2, CAT, and GCLC were increased (P < 0.05) and GSR were decreased (P < 0.05) by 0.1% TAU. In the intestinal epithelial cells, TAU treatment decreased (P < 0.05) SOD activity, increased (P < 0.05) CAT activity, and decreased (P < 0.05) the mRNA and protein expression of Nrf2. In summary, partial substitution methionine for taurine (21-42%) has no influence on egg performance of hens. Taurine enhances the antioxidative capacity in hepatocyte but not in the enterocytes and if taurine could offer an improved effect on antioxidant capacity needs to be verified under oxidative stress-challenged conditions.

Biotin alleviates hepatic and intestinal inflammation and apoptosis induced by high dietary carbohydrate in juvenile turbot (Scophthalmus maximus L.)

Excessive dietary carbohydrate commonly impairs the functions of liver and intestine in carnivorous fish. In the present study, a 10-week feeding trial was carried out to explore the regulation of biotin on the hepatic and intestinal inflammation and apoptosis in turbot (Scophthalmus maximus L.) fed with high carbohydrate diets. Three isonitrogenous and isolipidic experimental diets were designed as follows: the CC diet with 18.6% of carbohydrate and 0.04 mg/kg of biotin, the HC diet with 26.9% of carbohydrate and 0.05 mg/kg of biotin, and the HCB diet with 26.9% of carbohydrate and 1.62 mg/kg of biotin. Results showed that high dietary carbohydrate (HC diet) impaired the morphology of liver and intestine, however, inclusion of dietary biotin (HCB diet) normalized their morphology. Inflammation-related gene expression of nuclear factor κB p65 (nf-κb p65), tumor necrosis factor α (tnf-α), interleukin-1β (il-1β), il-6 and il-8, and the protein expression of NF-κB p65 in the liver and intestine were significantly up-regulated in the HC group compared to those in the CC group (P < 0.05), the HCB diet decreased their expression compared to the HC group (P < 0.05). The gene expression of il-10 and transforming growth factor-β (tgf-β) in the liver and intestine were significantly decreased in the HC group compared to the CC group (P < 0.05), and inclusion of dietary biotin increased the il-10 and tgf-β expression in the liver and intestine (P < 0.05). Moreover, compared to the CC group, the HC group had a stronger degree of DNA fragmentation and more TUNEL-positive cells in the liver and intestine, and the HCB group had a slighter degree of DNA fragmentation and fewer TUNEL-positive cells compared to the HC group. Meanwhile, the gene expression of B-cell lymphoma protein-2-associated X protein (bax) and executor apoptosis-related cysteine peptidase 3 (caspase-3) were significantly up-regulated and the gene expression of B-cell lymphoma-2 (bcl-2) was significantly down-regulated both in the liver and intestine in the HC group compared with those in the CC group (P < 0.05). Inclusion of dietary biotin significantly decreased the bax and caspase-3 mRNA levels and increased bcl-2 mRNA level in the liver and intestine (P < 0.05). In conclusion, high dietary carbohydrate (26.9% vs 18.6%) induced inflammation and apoptosis in liver and intestine. Supplementation of biotin (1.62 mg/kg vs 0.05 mg/kg) in diet can alleviate the high-dietary-carbohydrate-induced hepatic and intestinal inflammation as well as inhibit apoptosis in turbot. The present study provides basic data for the application of biotin into feed, especially the high-carbohydrate feed for turbot.

Additional supplementation of sulfur-containing amino acids in the diets improves the intestinal health of turbot fed high-lipid diets

An eight-week feeding trial was conducted to investigate the effects of diets supplemented with three sulfur-containing amino acids (SAA), namely, methionine, cysteine, and taurine, on the intestinal health status of juvenile turbot (Scophthalmus maximus) fed high-lipid diets. Four diets were formulated, namely, a high-lipid control diet (16% lipid, HL) and three SAA-supplemented diets, which were formulated by supplementing 1.5% methionine (HLM), 1.5% cysteine (HLC), and 1.5% taurine (HLT) into the HL control diet, respectively. Each diet was assigned to triplicate tanks, and each tank was stocked with 30 juvenile fish (appr. initial weight, 8 g). The histological and morphometric results showed that dietary SAA supplementation obviously improved the intestinal morphology and integrity, in particular as reflected by higher height of microvilli and mucosal folds. Dietary SAA supplementation, in particular cysteine, up-regulated the gene expression of mucin-2 and tight junction proteins (ZO-1, Tricellilun and JAM). Dietary SAA supplementation remarkably down-regulated the gene expression of apoptosis-related factors such as p38, JNK, and Bax, expression of pro-inflammatory factors (e.g., NF-κB, AP-1 IL-1β, IL-8, and TNF-α). SAA supplementation resulted in higher antioxidative abilities in the intestine. Additionally, dietary SAA supplementation largely altered the communities of intestinal microbiota. Compared with the HL group, higher relative abundance of potential beneficial bacteria, and lower relative abundance of opportunistic pathogens were observed in SAA-supplemented groups. Dietary taurine supplementation significantly increased the relative abundance of Ligilactobacillus (in particular Lactobacillus murinus) and Limosilactobacillus (especially Lactobacillus reuteri). In conclusion, dietary sulfur-containing amino acids supplementation have promising potential in ameliorating the intestinal inflammation of turbot fed high-lipid diets. Especially dietary cysteine and taurine supplementation have more positive effects on the communities of the intestinal microbiota of turbot.

The Benefit of Optimal Dietary Lipid Level for Black Seabream Acanthopagrus schlegelii Juveniles under Low-Salinity Environment

The present study was aimed at evaluating the regulatory effects of dietary lipid levels on growth performance, osmoregulation, fatty acid composition, lipid metabolism, and physiological response in Acanthopagrus schlegelii under low salinity (5 psu). An 8-week feeding trial was conducted in juvenile A. schlegelii with an initial weight of 2.27 ± 0.05 g, and six isonitrogenous experimental diets were formulated with graded levels of lipid: 68.7 g/kg (D1), 111.7 g/kg (D2), 143.5 g/kg (D3), 188.9 g/kg (D4), 239.3 g/kg (D5), and 269.4 g/kg (D6), respectively. Results indicated that fish fed with diet containing 188.9 g/kg lipid significantly improved growth performance. Dietary D4 improved ion reabsorption and osmoregulation by increasing the concentrations of Na⁺, K⁺, and cortisol in serum and activities of Na⁺/K⁺-ATPase as well as expression levels of osmoregulation related to gene expression levels in the gill and intestine. The expression levels of long chain polyunsaturated fatty acid biosynthesis-related genes were dramatically upregulated when dietary lipid levels increased from 68.7 g/kg to 189.9 g/kg with levels of docosahexaenoic (DHA), eicosapentaenoic (EPA), and DHA/EPA ratio being highest in the D4 group. When fish fed dietary lipid levels from 68.7 g/kg to 188.9 g/kg, lipid homeostasis could be maintained by upregulating sirt1 and pparα expression levels, whereas lipid accumulation was observed in dietary lipid levels of 239.3 g/kg and over. Fish fed with high dietary lipid levels resulted in physiological stress related to oxidative stress and endoplasmic reticulum stress. In conclusion, based on weight gain, the optimal dietary lipid requirement of juvenile A. schlegelii reared at low-salinity water is 196.0 g/kg. These findings indicate that the optimal dietary lipid level can improve growth performance, n-3 LC-PUFA accumulation, and osmoregulatory ability and maintain lipid homeostasis and normal physiological functions of juvenile A. schlegelii.

Taurine can improve intestinal function and integrity in juvenile Rhynchocypris lagowskii Dybowski fed high-dose glycinin

The present study evaluated the protective effect and the regulatory mechanism of taurine on growth inhibition and intestinal damage induced by glycinin in juvenile Rhynchocypris lagowskii Dybowski. The control diets had no glycinin and taurine, the glycinin diets contained only 80 g/kg glycinin, and the glycinin + taurine diets contained 80 g/kg glycinin+10 g/kg taurine. Juvenile Rhynchocypris lagowskii Dybowski (4.65 ± 0.03 g/tail) were respectively fed with these 3 diets for 8 weeks. The results showed that glycinin significantly decreased the final body weight, weight gain rate, specific growth rate, protein efficiency rate, feed efficiency rate and feeding rate of fish compared with the control group (P < 0.05). While taurine supplementation improved the growth performance and feed efficiency, but final body weight, weight gain rate, specific growth rate of the glycinin + taurine group were still significantly lower than the control group (P < 0.05). Compared with the glycinin group, taurine supplementation significantly increased whole-body and muscle crude protein content, and hepatopancreas and intestinal protease activities (P < 0.05). Distal intestinal villous dysplasia and mucosal damage, and increased intestinal mucosal permeability were observed in the glycinin group, while taurine supplementation alleviated these adverse effects. Usefully, taurine supplementation could also partially restore the impaired immune function and antioxidant capacity of fish fed glycinin diets. Compared with the glycinin group, taurine supplementation down-regulated pro-inflammatory cytokines TNF-α and IL-1β mRNA levels, and up-regulated anti-inflammatory cytokines IL-10 and TGF-β mRNA levels. Furthermore, taurine partially reversed the reduction of antioxidant genes Nrf2、HO-1, CAT and GPx mRNA levels in distal intestine induced by glycinin. Concluded, 80 g/kg glycinin led to intestinal damage, digestive dysfunction and increased intestinal mucosal permeability in juvenile Rhynchocypris lagowskii Dybowski, and these adverse effects were ultimately manifested in growth inhibition. But taurine supplementation could partially mitigate the negative effects induced by glycinin.

Taurine inhibits hydrogen peroxide-induced oxidative stress, inflammatory response and apoptosis in liver of Monopterus albus

Fish are extremely vulnerable to environmental stimulation and produce oxidative stress. Among them, hydrogen peroxide is an oxidative stress source that cannot be ignored in fish, which can cause physical disorders, inflammation and even death. Taurine was revealed to reduce oxidative damage and inflammation caused by toxic substances, but whether it can reduce toxicity of rice field eel caused by H₂O₂ has not been determined. Thus, the intervention effects of taurine on H₂O₂-induced oxidative stress, inflammation, apoptosis, and autophagy in rice field eel. The results showed that oxidative injury in the liver was determined after H₂O₂ injection, as indicated by enhanced serum AST and ALT activities, inhibited the antioxidant function (increased MDA and ROS contents, decreased antioxidant enzymes, inhibited nrf2 transcription level), and induced inflammatory response (upregulated il-1β, il-6, il-8, and il-12β gene expression, downregulated tgf-β1 gene expression, activated the transcription level of nf-κb, tlr-3, and tlr-7). In addition, bax, caspase3, beclin1, and Lc3B gene expression were significantly upregulated after H₂O₂ injection, while bcl2 and p62 gene expression were downregulated, leading to the occurrence of apoptosis and autophagy. In contrast, adding 0.2 and 0.5% taurine to feed significantly alleviated this damage, as indicated by the recovery of the aforementioned bioindicators, and the effect of 0.5% taurine addition is better than 0.2%. Overall, these results suggested that taurine can relieve the liver toxicity induced by H₂O₂, which enriched the toxic mechanism of H₂O₂ on fish and provided evidence for the protective effect of taurine on liver.

New insights into the influence of myo-inositol on carbohydrate metabolism during osmoregulation in Nile tilapia (Oreochromis niloticus)

A two-factor (2 × 3) orthogonal test was conducted to investigate the effects of dietary myo-inositol (MI) on the osmoregulation and carbohydrate metabolism of euryhaline fish tilapia (Oreochromis niloticus) under sustained hypertonic stress (20 practical salinity units [psu]). 6 diets containing either normal carbohydrate (NC, 30%) or high carbohydrate (HC, 45%) levels, with 3 levels (0, 400 and 1,200 mg/kg diet) of MI, respectively, were fed to 540 fish under 20 psu for 8 weeks. Dietary MI supplementation significantly improved growth performance and crude protein content of whole fish, and decreased the content of crude lipid of whole fish (P < 0.05). Curled, disordered gill lamella and cracked gill filament cartilage were observed in the gill of fish fed diets without MI supplementation. The ion transport capacity in gill was significantly improved in the 1,200 mg/kg MI supplementation groups compared with the 0 mg/kg MI groups (P < 0.05). Moreover, the contents of Na⁺, K⁺, Cl⁻ in serum were markedly reduced with the dietary MI supplementation (P < 0.05). The fish fed 1,200 mg/kg MI supplementation had the highest MI content in the gills and the lowest MI content in the serum (P < 0.05). Additionally, the fish fed with 1,200 mg/kg MI supplementation had the highest MI synthesis capacity in gills and brain (P < 0.05). Dietary MI markedly promoted the ability of carbohydrate metabolism in liver (P < 0.05). Moreover, fish in the 1,200 mg/kg MI groups had the highest antioxidant capacity (P < 0.05). This study indicated that high dietary carbohydrate would intensify stress, and impair the ability of osmoregulation in tilapia under a long-term hypersaline exposure. The supplementation of MI at 1,200 mg/kg in the high carbohydrate diet could promote carbohydrate utilization and improve the osmoregulation capacity of tilapia under long-term hypertonic stress.

Bacillus amyloliquefaciens protects Nile tilapia against Aeromonas hydrophila infection and alleviates liver inflammation induced by high-carbohydrate diet

Carbohydrates are widely distributed in nature as an important nutritional substance and energy source. However, the utilization efficiency of carbohydrates is very poor in fish. Over consumption of carbohydrates will cause excessive inflammatory response and result in lower pathogen resistance in fish. Probiotics have been widely used to prevent inflammation, but the underlying mechanism still needs more exploration. In this study, three diets, including a control diet (CD), a high-carbohydrate diet (HD) and the HD supplemented with Bacillus amyloliquefaciens SS1 (HDB) were used to feed Nile tilapia for 10 weeks. At the end of the feeding trial, fish were challenged with Aeromonas hydrophila (A. hydrophila) for 7 days. The data showed that the addition of Bacillus amyloliquefaciens SS1 (B. amyloliquefaciens SS1) significantly increased the survival rate and enhanced the respiratory burst activity of head kidney leukocytes in Nile tilapia. B. amyloliquefaciens SS1 treatment significantly elevated the anti-oxidative capability, which was evidenced by higher activities of superoxide dismutase (SOD) and total antioxidant capacity (T-AOC), and higher content of reduced glutathione (GSH) in the serum. Administration with B. amyloliquefaciens SS1 effectively suppressed inflammatory response in the liver by inhibiting nuclear factor kappa-B (NF-κB)/interleukin-1 beta (IL-1β) inflammatory signaling pathway. In vitro analysis suggested that intestinal bacteria derived-acetate has the antioxidant capability, which may account for the alleviation of inflammation. Overall, this study demonstrated that dietary supplementation with B. amyloliquefaciens SS1 protected Nile Tilapia against A. hydrophila infection and suppressed liver inflammation by enhancing antioxidant capability.

Sanguinarine attenuates hydrogen peroxide-induced toxicity in liver of Monopterus albus: Role of oxidative stress, inflammation and apoptosis

In aquatic animals, hydrogen peroxide (H₂O₂), which is a source of oxidative stress, can cause physiological dysfunction, inflammation, and death. Sanguinarine (SAN) is a plant extract known to improve antioxidant and immune capacity. However, the roles of SAN in H₂O₂-induced liver tissue toxicity is unclear. The effects on hepatic oxidative damage, inflammatory response, and apoptosis were investigated by feeding rice field eel with 0, 375, and 750 μg/kg of SAN for eight weeks and then intraperitoneally injected with H₂O₂. The results showed that after 24 h of H₂O₂ injection, the activities of ALT and AST in serum were significantly increased, oxidative damage and inflammatory response occurred in the liver, and apoptosis was induced, which indicated that H₂O₂ induced liver damage in rice field eel. However, dietary supplemented with 375 or 750 μg/kg SAN significantly decreased the activities of ALT and AST in serum, and significantly increased the antioxidant function (decreased ROS, MDA, and antioxidant enzymes levels, downregulated antioxidant-related gene expression, and inhibited the transcription level of nrf2). The addition of SAN at 375 or 750 μg/kg ameliorated H₂O₂-induced inflammatory response of liver (upregulated tgf-β1 mRNA expression, downregulated il-1β, il-6, il-8, and il-12β mRNA expression, and inhibited the transcription levels of tlr-3 tlr-7, and nf-κb). In addition, dietary supplemented with 375 or 750 μg/kg SAN alleviated the apoptosis of liver induced by H₂O₂ (downregulated bax mRNA expression, upregulated caspase3 mRNA expression, and reduced the number of apoptotic cells by TUNEL staining). Overall, these results suggested that SAN could alleviate the liver injury in rice field eel induced by H₂O₂, mainly by improving antioxidant capacity, alleviating inflammatory response and inhibiting apoptosis, and the effect of 750 μg/kg SAN addition is better than 375 μg/kg.

Taurine alleviates endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in the muscle cells of olive flounder (Paralichthysolivaceus)

The aim of the present study was to evaluate the effects of taurine on endoplasmic reticulum stress, inflammatory cytokine expression and mitochondrial oxidative stress induced by high glucose in primary cultured muscle cells of olive flounder (Paralichthys olivaceus). Three experimental groups were designed as follows: muscle cells of olive flounder incubated with three kinds of medium containing 5 mM glucose (control), 33 mM glucose (HG) or 33 mM glucose + 10 mM taurine (HG + T), respectively. Results showed that taurine addition significantly alleviated the decreased activity of superoxide dismutase (SOD) and the ratio of reduced to oxidized glutathione (GSH/GSSG) induced by high glucose. The increase of cellular reactive oxygen species (ROS), malondialdehyde content and cell apoptosis induced by high glucose were alleviated by taurine. Besides, gene expression of glucose-regulated protein 78, PKR-like ER kinase, tumor necrosis factor-α, interleukin-6, interleukin-1β, interleukin-8, muscle atrophy F-box protein and muscle RING-finger protein 1 were significantly up-regulated in the HG group, and taurine addition decreased the expression of these genes. High glucose led to the swelling of the endoplasmic reticulum (ER). Meanwhile, the nuclear translocation of nuclear factor κB (NF-κB) and the release of cytochrome C from mitochondria induced by high glucose were suppressed by taurine addition. These results demonstrated that taurine alleviated ERS, inflammation and mitochondrial oxidative stress induced by high glucose in olive flounder muscle cells. The ROS production, NF-κB signaling pathway and mitochondria function were the main targets of the biological effects of taurine under high glucose condition.

Oyster broth concentrate and its major component taurine alleviate acute alcohol‐induced liver damage

Our previous study showed that oyster hydrolysate (OH) protected against the liver damage caused by a single instance of ethanol (EtOH) binge drinking. Oyster broth concentrate (OBC) was discovered in the process of searching for a different substance derived from oysters (Crassostrea gigas) with economic value. OBC is a by‐product of boiling oysters at 95°C for 3 min. In this study, we investigated the effects of OBC and its major component taurine on blood and liver tissues obtained from a single‐EtOH‐binge‐drinking mouse model. The preadministration of OBC enhanced EtOH metabolism by increasing the activities of alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), and catalase. In addition, the preadministration of OBC reduced cytochrome P450 2E1 (CYP2E1) activity, reactive oxygen species (ROS) generation, Ca²⁺ concentrations, apoptotic signals, and inflammatory mediators in liver tissues. The reduction of apoptotic and inflammatory signals by OBC resulted from the downregulation of endoplasmic reticulum (ER) stress molecules and NF‐κB activity. Taurine administration showed similar effects to OBC. These results show that OBC protected against acute EtOH‐induced liver damage through the action of taurine. Our findings suggest that OBC could be an economically valuable substance and a functional food with hepatoprotective effects.

The Protective Effect of Taurine on Oxidized Fish-Oil-Induced Liver Oxidative Stress and Intestinal Barrier-Function Impairment in Juvenile Ictalurus punctatus

Dietary lipids provide energy for growth and development and provide fatty acids necessary for normal structure and biological function. However, oxidized lipids cause oxidative stress and intestinal damage. An 8-week feeding trial with fresh fish oil (FFO, control group), oxidized fish oil (OFO), and taurine-supplemented diets (OFOT, OFO + 0.2% of taurine) was conducted to evaluate the protective effect of taurine on oxidized fish-oil-induced liver oxidative stress and intestine impairment in juvenile Ictaluruspunctatus. The results showed that (1) Growth performance was significantly lower in fish fed OFO than in those fed other diets, whereas the opposite occurred in the hepatosomatic index. (2) OFO-feeding significantly increased lipid deposition compared with the FFO group. The addition of taurine ameliorated the OFO-induced increase in lipid vacuolization in the liver, significantly upregulated lpl mRNA expression, and downregulated fas and srebp1 mRNA expression. (3) OFO-feeding significantly reduced oxidative damage of liver. Compared with the OFO group, the OFOT group remarkably upregulated antioxidant enzyme mRNA expression through the Nrf2-Keap1 signaling pathway based on the transcriptional expression. (4) OFO diets induced intestinal physical and immune barrier damage. Compared with the OFO group, OFOT diets remarkably downregulated il-1β, il-6, tnf-α, and il-8 mRNA expression and upregulated tgf-β mRNA expression through the NF-κB signaling pathway. Besides, the addition of taurine to OFO diets significantly upregulated zo-2 and zo-1 mRNA expression, and downregulated claudin-15 and claudin-12 mRNA expression. In conclusion, oxidized-fish-oil diets can cause negative physiological health effects in Ictaluruspunctatus, while adding taurine can increase growth and antioxidant ability, reduce lipid deposition, and improve intestinal health.