Effects of high-fat diet on growth performance, lipid accumulation and lipid metabolism-related MicroRNA/gene expression in the liver of grass carp (Ctenopharyngodon idella)

Effects of α-lipoic acid (LA) supplementation in high-fat diet on the growth, glycolipid metabolism and liver health of largemouth bass (Micropterus salmoides)

An 8-week feeding trial was conducted to investigate the effects of LA supplementation in a high-fat diet on the growth performance, hepatic antioxidant capacity, and glycogen metabolism of largemouth bass (Micropterus salmoides). Five diets were formulated including control diet (11.55 % crude fat, CF), a high-fat diet (17.80 % crude fat, HF) and three HF diets supplemented with 0.15 %, 0.20 % and 0.25 % LA (HL0.15, HL0.20 and HL0.25, respectively). In this experiments, HL0.15 and HL0.20 could improve the uniform for the growth of the largemouth bass, while adding 0.25 % did not significantly improve growth. The highest viscerosomatic index (VSI) and hepatosomatic index (HSI) were measured in fish fed the HF diet. Compared to the fish fed HF diet, fish fed HL diets showed lower serum total triglyceride (TG), alanine aminotransferase (ALT), aspartate aminotransferase (AST), hepatic malondialdehyde (MDA) and glycogen levels, and higher hepatic catalase (CAT) and glutathione peroxidase (GSH-PX) activities. In addition, the mRNA expression for lipolysis genes in fish liver were increased and for gluconeogenesis and fatty acid synthesis were reduced. The transcript levels of apoptosis-related genes were significantly down-regulated in the liver of largemouth bass in HL0.15 and HL0.20 groups compared to the HF group. Moreover, compared with the HF group, the mRNA expression of pro-inflammatory factors was significantly reduced in HL groups, and the histomorphology of the liver were significantly improved. These results suggested that LA supplementation in high-fat diets could improve lipid utilization, glycogen accumulation, antioxidant capacity of fish liver, thus reduce the adverse effects of high fat diets on fish, and then improve the growth performance of largemouth bass.

Binding site redundancy is critical for the regulation of fas by miR-30c in blunt snout bream (Megalobrama amblycephala)

MiR-30c and fatty acid synthase (fas) both play important roles in physiological processes such as lipid synthesis and fat metabolism. Predictive analysis revealed that fas is a target gene of miR-30c with multiple seed sites. Seed sites are useful to predict miRNA targeting relationships; however, detailed analyses of seed sites in fish genomes remain poorly studied. In this study, the regulatory relationship between miR-30c and fas, number and effect of seed regions, and mechanism by which miR-30c regulates lipid metabolism were evaluated in blunt snout bream (Megalobrama amblycephala). Four miR-30c target sites for fas were identified using various prediction tools. miR-30c mimics were transfected into 293 T cells, and dual-luciferase reporter assays were used to evaluate the roles of different fas target sites. When a single target site was mutated, relative luciferase activity was higher than that in the control group, with different activity levels depending on the mutation site. When multiple target sites were mutated, relative luciferase activity increased significantly as the number of mutation sites increased and was the highest when the four sites were mutated simultaneously. The miR-30c agomir was injected into the abdominal cavity of M. amblycephala at various concentrations for analyses of physiological and biochemical parameters in the liver and blood and the expression of genes related to lipid metabolism in the liver. Total cholesterol, free fatty acid, triglyceride, and low density lipoprotein levels were significantly lower after miR-30c agomir injection comparing to the control (P < 0.05). Additionally, the expression levels of genes related to lipid metabolism were significantly lower after miR-30c agomir injection than in the control (P < 0.05). In summary, this study identified four specific miR-30c target sites in the 3' UTR of fas mRNA; the effects of these sites are cumulative, and the redundancy ensures the accurate regulation of fas during evolution. In addition, miR-30c has a negative regulatory effect on fas and regulates lipid metabolism via various genes related to this process. Therefore, the regulation of miR-30c can effectively ameliorate the side effects of a high-fat diet on liver function in M. amblycephala.

Tryptophan supplements in high-carbohydrate diets by improving insulin response and glucose transport through PI3K-AKT-GLUT2 pathways in blunt snout bream (Megalobrama amblycephala)

The aim of this experiment was to elucidate the metabolic ramifications of tryptophan supplementation in the context of high-carbohydrate diet-feeding, which is important for improving feeding strategies in aquaculture in order to improve fish carbohydrate metabolism. Juvenile blunt snout bream with an initial mean body mass of 55.0±0.5 g were allocated to consume one of three experimental diets: CN, a normal diet with carbohydrate content of 30% (w/w); HC, a diet with high carbohydrate content of 43% (w/w); and HL, a high-carbohydrate diet to which 0.8% L-tryptophan (L-trp) had been added. These diets were fed for 8 weeks, and the effects of the carbohydrate and tryptophan contents of the diets were assessed. Histological analysis using Hematoxylin and Eosin (H&E) and Oil Red O staining revealed that high-carbohydrate intake was associated with abnormal hepatocyte morphology and excessive liver lipid accumulation, which were notably ameliorated by tryptophan supplementation. A significant increase in plasma glucose, glucagon, AGEs (advanced glycation end products), triglycerides, total cholesterol, and a significant decrease in insulin and hepatic glycogen after a high-carbohydrate diet in terms of plasma indices, compared to the control group. Almost all of them were restored to the normal level in the HL group. The present study might preliminarily suggest that tryptophan supplementation ameliorates the imbalance in glucose metabolism of this species induced by a high-carbohydrate diet. Transcriptomics showed that glucose metabolism under high carbohydrate was mainly regulated by the PI3K-AKT signaling pathway. The mRNA expression and protein levels of GLUT2 also varied with this pathway, which would suggest that sustained activation of this pathway with the addition of tryptophan accelerates glucose transport and insulin secretion under high-carbohydrate diet. Subsequent GTT and ITT experiments have also demonstrated that tryptophan improves glucose tolerance and insulin tolerance in blunt snout bream on a high-carbohydrate diet. In conclusion, these findings elucidate the positive regulatory effect of tryptophan on the PI3K-AKT-GLUT2 pathway under a high carbohydrate diet and provide a theoretical basis for the subsequent rational application of high carbohydrate diets in the future.

Fibroblast growth factor 1 (FGF1) improves glucose homeostasis, modulates gut microbial composition, and reduces inflammatory responses in rainbow trout (Oncorhynchus mykiss) fed a high-fat diet

High-fat diets (HFDs) are widely used in aquaculture due to their lipid and protein-conserving effects, thereby reducing feed costs. However, prolonged feeding of HFD often leads to metabolic disorders in fish, such as disruption of hepatic lipid homeostasis, liver injury, and disruption of glucose homeostasis. Fibroblast growth factor 1 (FGF1) plays an essential role in controlling glucose levels in the body and dampening immune reactions. However, its impact on teleosts remains poorly researched. The therapeutic potential of recombinant FGF1 (rFGF1) was examined in a 6-week culture experiment involving rainbow trout (Oncorhynchus mykiss) that were fed an HFD. The results revealed that rFGF1 significantly reduced serum glucose levels and hepatic PEPCK and G6PC activities, but improved hepatic glycogen (P < 0.05), compared to the HFD + PBS group. Further experiments indicated that the inhibitory effect of rFGF1 on hepatic gluconeogenesis was mediated by the cAMP signaling pathway and was dependent on the high expression of PDE4D. In addition, rFGF1 increased hepatic glycogen content, which involves the AKT-GSK3β axis. Despite this increase, rFGF1 did not lead to glycogen storage disease, as shown by reduced hepatic inflammation as a result of decreased GOT (glutamic oxaloacetic transaminase), GPT (glutamic pyruvic transaminase), and elevated SOD (superoxide dismutase) in the rFGF1-treated group, accompanied by decreased il-1β, il-6, and xbp-1, and elevated nrf2 and number of hepatocyte autophagosomes. Alterations in gut microbes and short-chain fatty acids (SCFAs) were noted, indicating that rFGF1 caused a notable rise in intestinal Lactobacillus, acetic acid, and butyric acid levels. This study investigated the molecular mechanisms of rFGF1 on glucose metabolism and inflammatory responses in an HFD-fed rainbow trout model, providing new insights to improve the regulation of glucose metabolism in carnivorous fish.

Effects of Dietary Lipid Levels on the Growth, Muscle Fatty Acid and Amino Acid Composition, Antioxidant Capacity, and Lipid Deposition in Mirror Carp (Cyprinus carpio)

In fish, increasing the crude lipid level of feed can save protein and improve feed utilization. Mirror carp (Cyprinus carpio) is one of the most widely farmed fish species in the world. In this study, mirror carp larvae were fed isonitrogenous diets with different lipid levels (3%, 5%, 7%, 9%, 11%, and 13%). The rearing trial lasted for eight weeks. The results revealed that when the fat content was 9%, the AWGR, WGR, and FCR were highest, whereas FCR was lowest. The AWGR was correlated with the dietary lipid level, and the regression equation was y = -2.312x2 + 45.01x + 214.49. Compared with those in the control group, the T-CHO and TG contents were significantly greater in the 13% lipid content groups and significantly lower in the 9% lipid content groups (p < 0.05). In terms of muscle quality, the contents of MUFAs, PUFAs, and DHA + EPA were significantly greater than those in the other experimental groups (p < 0.05). Oil red O staining revealed a lipid content of 13% with severe fat deposition. In addition, the results of the analysis of antioxidant enzyme activity revealed that the activities of GSH, CAT and T-AOC were significantly greater at the 9% lipid content, and that the MDA content was significantly greater at the 13% lipid content (p < 0.05). Similarly, the mRNA levels of GH, IGF-I, FAS, and LPL were significantly highest at a lipid level of 9% (p < 0.05). The above results revealed that the optimal dietary lipid requirement for the fast growth of mirror carp (6.86 ± 0.95 g) was 9.74% on the basis of nonlinear regression analysis of the AWGR. The dietary lipid level (9%) improved the growth, stress resistance, and lipid utilization of mirror carp to a certain extent.

Effects of Dietary Fish Oil Supplementation on the Growth, Proximate Composition, and Liver Health of Chinese Stripe-Necked Turtle (Mauremys sinensis)

Dietary lipids provide energy for animals and can also be converted into other nutrients (such as non-essential amino acids), which play a role in saving protein. The Chinese stripe-necked turtle is a protected and endangered species that has been bred in captivity; however, basic data on lipid requirements remain unavailable. In this study, 360 Mauremys sinensis (body weight of 65.32 ± 0.15 g) were randomly divided into six groups with three replicates per group; the turtles were fed experimental diets supplemented with various levels of fish oil (i.e., 1% (control group, CG), 3.5% (HF-1), 6% (HF-2), 8.5% (HF-3), 11% (HF-4), and 13.5% (HF-5)) for 10 weeks. The results showed that compared with CG, increasing the fish oil level promoted the growth performance of turtles, and the HF-3 group achieved the best effect. The HF-4 group showed the highest increases in the hepatosomatic index and viscerosomatic index. In addition, increased lipid levels also increased the crude lipid content and reduced the crude protein content in muscle tissue. Oil red O staining showed that the liver lipid content increased with the level of supplemented fish oil, which is consistent with the results of the hepatosomatic index. Compared with CG, triglyceride, total cholesterol, and low-density lipoprotein cholesterol increased significantly in both the liver and serum when fish oil levels exceeded 8.5% (p < 0.05), while high-density lipoprotein cholesterol decreased significantly. Aspartate transaminase and cerealthirdtransaminase levels in serum increased significantly when fish oil levels exceeded 8.5% (p < 0.05). Moreover, the activities of antioxidant enzymes (GSH-Px, SOD, T-AOC, and CAT) and MDA showed similar results, indicating that high fish oil levels (8.5-13.5%) caused liver tissue damage in M. sinensis. Increased fish oil levels significantly upregulated the expression levels of cytokines (IFN-γ, TNF-α, TGF-β1, IL-10, and IL-12) (p < 0.05), downregulated the expression levels of antioxidant enzyme-related genes (cat, mn-sod, and gsh-px), and increased apoptosis of liver cells. Supplementation of the diet with 3.5-6% fish oil improved the growth performance of M. sinensis, and the turtles maintained a beneficial immune status. The results provide a scientific basis for optimizing the commercial feed formula of M. sinensis.

Dietary Chitosan Attenuates High-Fat Diet-Induced Oxidative Stress, Apoptosis, and Inflammation in Nile Tilapia (Oreochromis niloticus) through Regulation of Nrf2/Kaep1 and Bcl-2/Bax Pathways

Fatty liver injury is a prevalent condition in most farmed fish, yet the molecular mechanisms underpinning this pathology remain largely elusive. A comprehensive feeding trial spanning eight weeks was conducted to discern the potential of dietary chitosan in mitigating the deleterious effects of a high-fat diet (HFD) while concurrently exploring the underlying mechanism. Growth performance, haemato-biochemical capacity, antioxidant capacity, apoptotic/anti-apoptotic gene expression, inflammatory gene expression, and histopathological changes in the liver, kidney, and intestine were meticulously assessed in Nile tilapia. Six experimental diets were formulated with varying concentrations of chitosan. The first three groups were administered a diet comprising 6% fat with chitosan concentrations of 0%, 5%, and 10% and were designated as F6Ch0, F6Ch5, and F6Ch10, respectively. Conversely, the fourth, fifth, and sixth groups were fed a diet containing 12% fat with chitosan concentrations of 0%, 5%, and 10%, respectively, for 60 days and were termed F12Ch0, F12Ch5, and F12Ch10. The results showed that fish fed an HFD demonstrated enhanced growth rates and a significant accumulation of fat in the perivisceral tissue, accompanied by markedly elevated serum hepatic injury biomarkers and serum lipid levels, along with upregulation of pro-apoptotic and inflammatory markers. In stark contrast, the expression levels of nrf2, sod, gpx, and bcl-2 were notably decreased when compared with the control normal fat group. These observations were accompanied by marked diffuse hepatic steatosis, diffuse tubular damage, and shortened intestinal villi. Intriguingly, chitosan supplementation effectively mitigated the aforementioned findings and alleviated intestinal injury by upregulating the expression of tight junction-related genes. It could be concluded that dietary chitosan alleviates the adverse impacts of an HFD on the liver, kidney, and intestine by modulating the impaired antioxidant defense system, inflammation, and apoptosis through the variation in nrf2 and cox2 signaling pathways.

Optimal dietary lipid levels alleviated adverse effects of high temperature on growth, lipid metabolism, antioxidant and immune responses in juvenile turbot (Scophthalmus maximus L.)

Fish physiological health is often negatively impacted by high-temperature environments and there are few studies on how dietary lipids affect fish growth and physiology when exposed to heat stress. The main objective of this research was to examine the impact of dietary lipid levels on growth and physiological status of juvenile turbot (Scophthalmus maximus L.) and determine if dietary lipid concentration could alleviate the possible adverse effects of heat stress. Five diets containing 6.81%, 9.35%, 12.03%, 14.74%, and 17.08% lipid, respectively, were formulated and fed to turbot (initial weight 5.13 ± 0.02 g) under high-temperature conditions (24.0-25.0 °C). Meanwhile, the diet with 12.03% lipid (considered by prior work to be an optimal dietary lipid level) was fed to turbot of the same size at normal temperature. Results suggested that, among the different dietary lipid levels under high-temperature conditions, fish fed the optimal lipid (12.03%) exhibited better growth compared to non-optimal lipid groups, as evidenced by higher weight gain and specific growth rate. Simultaneously, the optimal lipid diet may better maintain lipid homeostasis, as attested by lower liver and serum lipid, along with higher liver mRNA levels of lipolysis-related genes (pgc1α, lipin1, pparα, lpl and hl) and lower levels of synthesis-related genes (lxr, fas, scd1, pparγ, dgat1 and dgat2). Also, the optimal lipid diet might mitigate oxidative damage by improving antioxidant enzyme activity, decreasing malondialdehyde levels, and up-regulating oxidation-related genes (sod1, sod2, cat, gpx and ho-1). Furthermore, the optimal lipid may enhance fish immunity, as suggested by the decrease in serum glutamic-oxalacetic/pyruvic transaminase activities, down-regulation of pro-inflammatory genes and up-regulation of anti-inflammation genes. Correspondingly, the optimal lipid level suppressed MAPK signaling pathway via decreased phosphorylation levels of p38, JNK and ERK proteins in liver. In summary, the optimal dietary lipid level facilitated better growth and physiological status in turbot under thermal stress.

Dietary Lycium barbarum Polysaccharide Modulates Growth Performance, Antioxidant Capacity, and Lipid Metabolism in Common Carp (Cyprinus carpio) Fed with High-Fat Diet

To investigate the ameliorative effects and mechanism of Lycium barbarum polysaccharide (LBP) on growth performance, oxidative stress, and lipid deposition in common carp (Cyprinus carpio) fed with high-fat diets, fish with an initial weight of 5.29 ± 0.12 g were divided into five experimental groups-including normal-fat diets, high-fat diets, and high-fat diets-supplemented with LBP (0.5, 1.0, and 2.0 g/kg) for 8 weeks. The results showed that high-fat diets resulted in significant decreases in final body weight, weight gain rate, and specific growth rate of fish, as well as causing a significant decrease in hepatic total antioxidant capacity, catalase, and glutathione peroxidase activities. These changes were accompanied by a significant decrease in lipase activity and ATP level and a significant increase in malondialdehyde content. The expression levels of lipid metabolism-related genes (acetyl coenzyme A carboxylase 1, stearoyl coenzyme A desaturase 1, fat synthase, peroxisome proliferator-activated receptor-γ, fructofuranose bisphosphatase, and glucose-6-phosphatase) were also markedly elevated by high-fat diets. Supplementation with 0.5-2.0 g/kg LBP in high-fat diets improved the reduced growth performance, increased hepatic total antioxidant enzymes, catalase, and glutathione peroxidase activities, and lowered malondialdehyde level in fish fed with high-fat diets. Additionally, dietary supplementation with LBP significantly downregulated hepatic gene expression levels of acetyl coenzyme A carboxylase 1, stearoyl coenzyme A desaturase 1, fat synthase, sterol regulatory element-binding protein 1, peroxisome proliferator-activated receptor-γ, fructofuranose bisphosphatase, and glucose-6-phosphatase. In conclusion, fish fed with high-fat diets demonstrated impaired growth performance, antioxidant capacity, and lipid metabolism, and dietary supplementation with 0.5-2.0 g/kg LBP ameliorated the impairments induced by high-fat diets.

Impact of Hydroxytyrosol-Rich Extract Supplementation in a High-Fat Diet on Gilthead Sea Bream (Sparus aurata) Lipid Metabolism

High-fat diets (HFDs) enhance fish growth by optimizing nutrient utilization (i.e., protein-sparing effect); however, their potential negative effects have also encouraged the search for feed additives. This work has investigated the effects of an extract rich in a polyphenolic antioxidant, hydroxytyrosol (HT), supplemented (0.52 g HT/kg feed) in a HFD (24% lipid) in gilthead sea bream (Sparus aurata). Fish received the diet at two ration levels, standard (3% of total fish weight) or restricted (40% reduction) for 8 weeks. Animals fed the supplemented diet at a standard ration had the lowest levels of plasma free fatty acids (4.28 ± 0.23 mg/dL versus 6.42 ± 0.47 in the non-supplemented group) and downregulated hepatic mRNA levels of lipid metabolism markers (ppara, pparb, lpl, fatp1, fabp1, acox1, lipe and lipa), supporting potential fat-lowering properties of this compound in the liver. Moreover, the same animals showed increased muscle lipid content and peroxidation (1.58- and 1.22-fold, respectively, compared to the fish without HT), suggesting the modulation of body adiposity distribution and an enhanced lipid oxidation rate in that tissue. Our findings emphasize the importance of considering this phytocompound as an optimal additive in HFDs for gilthead sea bream to improve overall fish health and condition.

Effects of Dietary Bile Acids on Growth Performance, Lipid Deposition, and Intestinal Health of Rice Field Eel (Monopterus albus) Fed with High-Lipid Diets

The purpose of this trial was to study the positive effects of bile acids (BAs) on growth performance and intestinal health of rice field eel fed with high-lipid diets (HLDs). Rice field eels (initial weight 17.00 ± 0.10 g) were divided into four groups, each group containing four repetitions and feeding with different isonitrogenous diet: control diet containing 7% lipid content, HLDs containing the lipid content increased to 13%, HLDs supplementing with 0.025% BAs and 0.05% BAs, respectively. After 8 weeks, compared control group, the fish fed HLDs had no significant effect on weight gain rate and specific growth rate (P > 0.05), but increased the lipid deposition in tissues and intestinal lipase activity, and damaged to intestinal oxidative stress, inflammatory response, physical barrier, and structural integrity (P < 0.05). Dietary BAs significantly increased weight gain rate and specific growth rate in fish fed with HL diets (P < 0.05) and reduced feed conversation rate (P < 0.05). Further, the eels fed with BAs reduced the total lipid content in liver, muscle, and whole body (P < 0.05). Dietary BAs decreased the activity of intestinal lipase (P < 0.05). Meanwhile, BAs supplemented in HLDs improved intestinal antioxidant capacity through increasing the activities of T-SOD (total superoxide dismutase), GSH-PX (glutathione peroxidase), CAT (catalase), T-AOC (total antioxidant capacity), whereas reducing MDA (malondialdehyde) content (P < 0.05). Moreover, dietary BAs regulated the mRNA expression related to inflammatory response, oxidative stress, and physical barrier in intestine, such as tnf-α, il-8, tlr-8, il-10, nrf2, keap1, claudin12, and claudin15 (P < 0.05). Dietary BAs supplementation also enhanced the intestinal structural integrity characterized by increased fold height and lamina propria width (P < 0.05). This study showed that dietary BAs supplemented in HLDs (13% lipid) could increase the growth performance of rice field eel, reduce lipid deposition in tissues and whole body, and enhance intestinal health.

Dietary nano-Se supplementation regulates lipid deposition, protein synthesis and muscle fibre formation in grass carp fed with high-fat diet

The current study aims to confirm the positive effects of dietary nano-Se on nutrients deposition and muscle fibre formation in grass carp fed with high-fat diet (HFD) before overwintering and to reveal its possible molecular mechanism. The lipid deposition, protein synthesis and muscle fibre formation in grass carp fed with regular diet (RD), HFD or HFD supplemented with nano-Se (0·3 or 0·6 mg/kg) for 60 d were tested. Results show that nano-Se significantly reduced lipid content, dripping loss and fibre diameter (P < 0·05), but increased protein content, post-mortem pH24 h and muscle fibre density (P < 0·05) in muscle of grass carp fed with HFD. Notably, dietary nano-Se decreased lipid deposition in the muscle by regulating amp-activated protein kinase activity and increased protein synthesis and fibre formation in muscle by activating target of rapamycin and myogenic determining factors pathways. In summary, dietary nano-Se can regulate the nutrients deposition and muscle fibre formation in grass carp fed with HFD, which exhibit potential benefit for improving flesh quality of grass carp fed with HFD.

Dietary cultured supernatant mixture of Cetobacterium somerae and Lactococcus lactis improved liver and gut health, and gut microbiota homeostasis of zebrafish fed with high-fat diet

Postbiotics have the ability to improve host metabolic disorders and immunity. In order to explore whether the postbiotics SWFC (cultured supernatant mixture of Cetobacterium somerae and Lactococcus lactis) repaired the adverse effects caused by feeding of high-fat diet (HFD), zebrafish were selected as the experimental animal and fed for 6 weeks, with dietary HFD as the control group, and HFD containing 0.3 g/kg and 0.4 g/kg SWFC as the treatment groups. The results indicated that addition of SWFC in the diet at a level of 0.3 and 0.4 g/kg didn't affect the growth performance of zebrafish (P > 0.05). Supplementation of dietary SWFC0.3 relieved lipid metabolism disorders through significant increasing in the expression of pparα and cpt1, and decreasing the expression of cebpα, pparγ, acc1 and dgat-2 genes (P < 0.05). Moreover, the content of triacylglycerol was markedly lower in the liver of zebrafish grouped under SWFC0.3 (P < 0.05). Dietary SWFC0.3 also improved the antioxidant capacity via increasing the expression level of ho-1, sod and gstr genes, and significant inducing malondialdehyde content in the liver of zebrafish (P < 0.05). Besides, dietary SWFC0.3 also notably improved the expression level of lysozyme, c3a, defbl1 and defbl2 (P < 0.05). The expression level of pro-inflammatory factors (nf-κb, tnf-α, and il-1β) were significantly decreased and the expression level of anti-inflammatory factor (il-10) was markedly increased in the postbiotics 0.3 g/kg group (P < 0.05). Feeding with SWFC0.3 supplemented diet for 6 weeks improved the homeostasis of gut microbiota and increased the survival rate of zebrafish after challenged with Aeromonus veronii Hm091 (P < 0.01). It was worth noting that the positive effect of dietary SWFC at a level of 0.3 g/kg was considerably better than that of 0.4 g/kg. This may imply that the effectiveness and use of postbiotics is limited by dosage.

Effects of dietary berberine on growth performance, lipid metabolism, antioxidant capacity and lipometabolism-related genes expression of AMPK signaling pathway in juvenile black carp (Mylopharyngodon piceus) fed high-fat diets

This study aimed to investigate the effects of high-fat diet (HFD) supplemented with berberine on growth, lipid metabolism, antioxidant capacity and lipometabolism-related genes expression of AMPK signaling pathway in juvenile black carp (Mylopharyngodon piceus). Five hundred and forty healthy fish (4.04 ± 0.01 g) were randomly distributed into six groups, and fed six experimental diets: normal-fat diet (NFD, 5% fat), HFD (15% fat), and four HFDs supplemented with graded levels of berberine, respectively. The results showed that, compared with fish fed NFD, HFD had no effects on the growth of fish except for reducing survival rate, whereas HFD caused extensive lipid accumulation, oxidative stress injury and hepatic abnormalities. However, compared with the HFD group, fish fed HFD containing an appropriate berberine (98.26 or 196.21 mg/kg) improved the growth performance, increased hepatic lipid metabolism and antioxidant enzymes activities, and up-regulated the mRNA expression levels of ampk subunits and lipolysis genes such as pparα, cpt-1, acox, atgl and hsl (P < 0.05). Meanwhile, HFD supplemented with an appropriate berberine reduced crude lipid contents in liver and whole-body, decreased serum lipid contents, and ALT and AST activities, and down-regulated the mRNA expression levels of lipogenesis genes such as srebp-1, acc1, gpat, fas and pparγ, and lipid transporter genes such as fatp, fabp and fat/cd36 (P < 0.05). Thus, HFD supplemented with an appropriate berberine could improve growth of black carp, promote lipid metabolism and enhance antioxidant capacity. The lipid-lowering mechanism of berberine might be mediated by activating AMPK pathway, up-regulating lipolysis genes expression, and down-regulating lipogenesis and transport genes expression.

Integrated Metabolome and Transcriptome Analyses Reveal the Efficacy of Steroidal Saponins for Glucose and Lipid Metabolism in Hybrid Grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) Fed Higher-Lipid Diets

An analysis of the extent of the effect of steroidal saponin addition on glucose and lipid metabolism in hybrid grouper liver was performed at the transcriptomic and metabolomic levels. Feeds (52% crude protein, 14% crude lipid) were prepared containing 0% (S0), 0.1% (S0.1), and 0.2% (S0.2) steroidal saponins. After eight weeks of feeding trial, compared to the S0 group, the activities of serum albumin, alanine aminotransferase, and aspartate transaminase were significantly lower and the activities of lysozyme, acid phosphatase, and alkaline phosphatase were significantly higher in the S0.1 group (p < 0.05). The superoxide dismutase, catalase, and glutathione peroxidase activities in the livers of the S0.1 group were significantly higher than those of the S0 group, while the malondialdehyde content was significantly lower than that of the S0 group (p < 0.05). There were forty-two differentially expressed genes and thirty-two differential metabolites associated with glucose and lipid metabolism enriched using KEGG and GO. In the S0 group, the expression of prostaglandin-endoperoxide synthase 1, prostaglandin E synthase 1, and thromboxane-2 synthase mRNA was significantly higher than in the S0.1 group (p < 0.05). The expression levels of genes in the S0 group were significantly higher than those in the S0.1 group (p < 0.05), including for glycogen synthase kinase, glucose-6-phosphatase catalytic subunit 2, fructose-1,6-bisphosphatase, phosphoenolpyruvate carboxykinase, glucose transporter 4, and malate dehydrogenase. The expression of mRNA such as fatty acid synthase, acetyl-CoA carboxylase, and sterol regulatory element-binding protein 1 was significantly lower in the S0.1 group than in the S0 group, while the expression of carnitine acyltransferase 1, acyl-CoA synthetase, and acyl-CoA dehydrogenase genes was significantly higher in the S0 group (p < 0.05). In summary, glycogen synthesis, gluconeogenesis, and the arachidonic acid metabolism pathway were inhibited by 0.1% steroidal saponins, and glycogenolysis, glycolysis, the tricarboxylic acid cycle, and the fatty acid β-oxidation pathway were activated. This study aims to provide a reference for the formulation of grouper feeds with a higher crude-lipid level.

Peroxisome Proliferator-Activated Receptor Signaling-Mediated 13-S-Hydroxyoctadecenoic Acid Is Involved in Lipid Metabolic Disorder and Oxidative Stress in the Liver of Freshwater Drum, Aplodinotus grunniens

The appropriate level of dietary lipids is essential for the nutrient requirements, rapid growth, and health maintenance of aquatic animals, while excessive dietary lipid intake will lead to lipid deposition and affect fish health. However, the symptoms of excessive lipid deposition in the liver of freshwater drums (Aplodinotus grunniens) remain unclear. In this study, a 4-month rearing experiment feeding with high-fat diets and a 6-week starvation stress experiment were conducted to evaluate the physiological alteration and underlying mechanism associated with lipid deposition in the liver of A. grunniens. From the results, high-fat-diet-induced lipid deposition was associated with increased condition factor (CF), viscerosomatic index (VSI), and hepatosomatic index (HSI). Meanwhile, lipid deposition led to physiological and metabolic disorders, inhibited antioxidant capacity, and exacerbated the burden of lipid metabolism. Lipid deposition promoted fatty acid synthesis but suppressed catabolism. Specifically, the transcriptome and metabolome showed significant enrichment of lipid metabolism and antioxidant pathways. In addition, the interaction analysis suggested that peroxisome proliferator-activated receptor (PPAR)-mediated 13-S-hydroxyoctadecenoic acid (13 (s)-HODE) could serve as the key target in regulating lipid metabolism and oxidative stress during lipid deposition in A. grunniens. Inversely, with a lipid intake restriction experiment, PPARs were confirmed to regulate lipid expenditure and physiological homeostasis in A. grunniens. These results uncover the molecular basis of and provide specific molecular targets for fatty liver control and prevention, which are of great importance for the sustainable development of A. grunniens.

Insights into the mechanism of growth and fat deposition by feeding different levels of lipid provided by transcriptome analysis of swamp eel (Monopterus albus, Zuiew 1793) liver

Lipid is an important source of energy in fish feeds, and the appropriate fat content can improve the efficiency of protein utilization. However, excessive lipid content in the feed can lead to abnormal fat deposition in fish, which has a negative effect on the growth of fish. Therefore, the effects of feed lipid levels on swamp eel were studied. Essential functional genes were screened using transcriptomics. We divided 840 fish into seven groups (four replicates). A mixture of fish and soybean oils (1:4), 0%, 2%, 4%, 6%, 8%, 10%, and 12% was added to the basic feed were named groups one to seven (L1-L7), respectively. Isonitrogenous diets were fed swamp eel for 10 weeks. Growth performance, visceral index, nutritional components, and biochemical indexes were measured and analyzed. Livers of the 0%, 6%, and 12% groups were subjected to transcriptome sequencing analysis. The results of our study showed that: the suitable lipid level for the growth of swamp eel was 7.03%; the crude fat content of whole fish, liver, intestine, muscle, and skin increased with the increase of lipid level, with some significant difference, and excess fat was deposited in skin tissue; triglyceride, total cholesterol, and free fatty acid contents increased with the increase of feed lipid level. High-density lipoprotein levels in the L3 and L4 groups were higher than in the other groups. Blood glucose concentrations in the L5, L6, and L7 groups increased; the liver tissue structure was damaged when the lipid level was too high. two-hundred-and-twenty-eight differentially expressed genes were found. Several critical pathways regulating glucose metabolism and energy balance (e.g., glycerolipid metabolism, glycolysis synthesis, degradation of ketone bodies, and Janus Kinase/Signal Transducer and Activator of Transcription signaling pathway) were enriched in swamp eel compared with the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Suitable lipid levels (7.03%) can promote the growth of swamp eel, and excessive lipid levels can cause elevated blood lipids and lead to liver cell damage. Regulatory mechanisms may involve multiple metabolic pathways for glucose and lipid metabolism in eels. This study provides new insights to explain the mechanism of fat deposition due to high levels of lipid and provides a basis for the production of efficient and environmentally friendly feed for swamp eel.

Effects of choline supplementation on growth performance, liver histology, nonspecific immunity and related genes expression of hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) fed with high-lipid diets

This study was conducted to evaluate the effect of dietary choline levels on growth performance, liver histology, nonspecific immunity and related gene expression of hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus) fed with high-lipid diets. The fish (initial body weight 6.86 ± 0.01 g) were fed diets containing different choline levels (0, 5, 10, 15, and 20 g/kg, named D1, D2, D3, D4, and D5, respectively) for 8 weeks. The results showed that:(1) dietary choline levels had no significant effect on final body weight (FBW), feed conversion rate (FCR), visceral somatic index(VSI) and condition factor (CF) compared with the control group (P > 0.05). However, the hepato somatic index (HSI) in the D2 group was significantly lower than that in the control group and the survival rate (SR) in the D5 group was significantly lower (P < 0.05). (2) with dietary choline level increasing, alkaline phosphatase (AKP) and superoxide dismutase (SOD) of serum showed a tendency to increase and then decrease, and the maximum values were obtained in the D3 group, but the contents of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) decreased significantly (P < 0.05). (3) Immunoglobulin M (IgM), lysozyme (LYZ), catalase (CAT), total antioxidative capacity (T-AOC), and SOD in the liver all showed a trend of first increase and then decrease with the dietary choline level increased, and all of them achieved the maximum value at D4 group (P < 0.05), while reactive oxygen species (ROS) and malondialdehyde (MDA) in the liver decreased significantly (P < 0.05). (4) results from liver sections suggest that appropriate levels of choline can improve cell structure, compared with the control group, the damaged histological morphology of the liver was relieved and even returned to normal in D3 group. (5) in the D3 group, choline significantly upregulated the expression of hepatic sod and cat mRNA, whereas the expression of cat in the D5 group was significantly lower than that in the control group (P < 0.05); And the supply of choline stimulated a significant down-regulation of interleukin 6 (il6), myeloid differentiation factor 8 (myd88), toll-like receptor 22 (tlr22) mRNA expression levels in liver, while the expression of cellular tumor antigen p53 (p53) and interleukin 10 (il10) showed an upward and then downward trend (P < 0.05). In general, choline can improve the immunity of hybrid grouper by regulating non-specific immune-related enzyme activity and gene expression and reducing oxidative stress induced by high-lipid diet.

Comparative Analysis of miRNA-mRNA Regulation in the Testes of Gobiocypris rarus following 17α-Methyltestosterone Exposure

17α-Methyltestosterone (17MT), a synthetic organic compound commonly found in sewage waters, can affect reproduction in aquatic animals, such as tilapia and yellow catfish. In the present study, male Gobiocypris rarus were exposed to 25, 50, and 100 ng/L of 17α-methyltestosterone (17MT) for 7 days. We first analyzed miRNA- and RNA-seq results to determine miRNA-target gene pairs and then developed miRNA-mRNA interactive networks after 17MT administration. Total weights, total lengths, and body lengths were not significantly different between the test groups and control groups. The paraffin slice method was applied to testes of G. rarus in the MT exposure and control groups. We found that there were more mature sperm (S) and fewer secondary spermatocytes (SSs) and spermatogonia (SGs) in the testes of control groups. As 17MT concentration increased, fewer and fewer mature sperm (S) were observed in the testes of male G. rarus. The results showed that FSH, 11-KT, and E2 were significantly higher in individuals exposed to 25 ng/L 17MT compared with the control groups. VTG, FSH, LH, 11-KT, and E2 were significantly lower in the 50 ng/L 17MT exposure groups compared to the control groups. VTG, FSH, LH, 11-KT, E2, and T were significantly lower in the groups exposed to 100 ng/L 17MT. High-throughput sequencing revealed 73,449 unigenes, 1205 known mature miRNAs, and 939 novel miRNAs in the gonads of G. rarus. With miRNA-seq, 49 (MT25-M vs. Con-M), 66 (MT50-M vs. Con-M), and 49 (MT100-M vs. Con-M) DEMs were identified in the treatment groups. Five mature miRNAs (miR-122-x, miR-574-x, miR-430-y, lin-4-x, and miR-7-y), as well as seven differentially expressed genes (soat2, inhbb, ihhb, gatm, faxdc2, ebp, and cyp1a1), which may be associated with testicular development, metabolism, apoptosis, and disease response, were assayed using qRT-PCR. Furthermore, miR-122-x (related to lipid metabolism), miR-430-y (embryonic development), lin-4-x (apoptosis), and miR-7-y (disease) were differentially expressed in the testes of 17MT-exposed G. rarus. This study highlights the role of miRNA-mRNA pairs in the regulation of testicular development and immune response to disease and will facilitate future studies on the miRNA-RNA-associated regulation of teleost reproduction.

Effects of Dietary Steroid Saponins on Growth Performance, Serum and Liver Glucose, Lipid Metabolism and Immune Molecules of Hybrid Groupers (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatu) Fed High-Lipid Diets

High-lipid diets are attributed to excessive lipid deposition and metabolic disturbances in fish. The aim of this experiment was to investigate the effects of steroidal saponins on growth performance, immune molecules and metabolism of glucose and lipids in hybrid groupers (initial weight 22.71 ± 0.12 g) fed high-lipid diets. steroidal saponins (0%, 0.1% and 0.2%) were added to the basal diet (crude lipid, 14%) to produce three experimental diets, designated S0, S0.1 and S0.2, respectively. After an 8-week feeding trial, no significant differences were found between the S0 and S0.1 groups in percent weight gain, specific growth rate, feed conversion ratio, protein efficiency ratio and protein deposition rate (p > 0.05). All those in the S0.2 group were significantly decreased (p < 0.05). Compared to the S0 group, fish in the S0.1 group had lower contents of serum triglyceride and low-density lipoprotein cholesterol and higher high-density lipoprotein cholesterol and glucose (p < 0.05). The activities of superoxide dismutase, catalase and glutathione peroxidase were significantly higher, and malondialdehyde contents were significantly lower in the S0.1 group than in the S0 group (p < 0.05). Hepatic triglyceride, total cholesterol and glycogen were significantly lower in the S0.1 group than in the S0 group (p < 0.05). Activities of lipoprotein lipase, total lipase, glucokinase and pyruvate kinase, and gene expression of lipoprotein lipase, triglyceride lipase and glucokinase, were significantly higher in the S0.1 group than in the S0 group. Interleukin-10 mRNA expression in the S0.1 group was significantly higher than that in the S0 group, while the expression of interleukin-6 and tumor necrosis factor-α genes were significantly lower than those in the S0 group. In summary, adding 0.1% steroidal saponins to a high-lipid diet not only promoted lipolysis in fish livers, but also activated glycolysis pathways, thus enhancing the utilization of the dietary energy of the groupers, as well as supporting the fish's nonspecial immune-defense mechanism.

High cholesterol intake remodels cholesterol turnover and energy homeostasis in Nile tilapia (Oreochromis niloticus)

The roles of dietary cholesterol in fish physiology are currently contradictory. The issue reflects the limited studies on the metabolic consequences of cholesterol intake in fish. The present study investigated the metabolic responses to high cholesterol intake in Nile tilapia (Oreochromis niloticus), which were fed with four cholesterol-contained diets (0.8, 1.6, 2.4 and 3.2%) and a control diet for eight weeks. All fish-fed cholesterol diets showed increased body weight, but accumulated cholesterol (the peak level was in the 1.6% cholesterol group). Then, we selected 1.6% cholesterol and control diets for further analysis. The high cholesterol diet impaired liver function and reduced mitochondria number in fish. Furthermore, high cholesterol intake triggered protective adaptation via (1) inhibiting endogenous cholesterol synthesis, (2) elevating the expression of genes related to cholesterol esterification and efflux, and (3) promoting chenodeoxycholic acid synthesis and efflux. Accordingly, high cholesterol intake reshaped the fish gut microbiome by increasing the abundance of Lactobacillus spp. and Mycobacterium spp., both of which are involved in cholesterol and/or bile acids catabolism. Moreover, high cholesterol intake inhibited lipid catabolic activities through mitochondrial β-oxidation, and lysosome-mediated lipophagy, and depressed insulin signaling sensitivity. Protein catabolism was elevated as a compulsory response to maintain energy homeostasis. Therefore, although high cholesterol intake promoted growth, it led to metabolic disorders in fish. For the first time, this study provides evidence for the systemic metabolic response to high cholesterol intake in fish. This knowledge contributes to an understanding of the metabolic syndromes caused by high cholesterol intake or deposition in fish.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00158-7.

DHA induces adipocyte lipolysis through endoplasmic reticulum stress and the cAMP/PKA signaling pathway in grass carp (Ctenopharyngodon idella)

Docosahexaenoic acid (DHA) is a biologically active fatty acid that reduces the accumulation of lipids. However, the molecular mechanism underlying this process, particularly in fish, is not well understood. Recent studies show that endoplasmic reticulum (ER) stress triggers the activation of the unfolded protein response, which has been revealed to play an essential role in lipid metabolism. In this study, we explored the effect of DHA on ER stress and investigated the potential molecular mechanisms underlying DHA-induced adipocyte lipolysis in grass carp (Ctenopharyngodon idella) both in vivo and in vitro. We found that DHA remarkably reduced the triglyceride content, increased the secretion of glycerol, promoted lipolysis in adipocytes and evoked ER stress, whereas inhibiting ER stress using 4-phenyl butyric acid (4-PBA) inhibited the effects of DHA (P < 0.05). These results implied that ER stress potentially participates in DHA-induced adipocyte lipolysis. Additionally, STF-083010, a specific inositol-requiring enzyme 1α (IRE1α)-inhibitor, attenuated the effects of DHA on lipolysis, demonstrating that IRE1α and X-box binding protein 1 potentially participate in DHA-induced lipolysis. DHA also activated the cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) pathway by increasing the level of cAMP and activating the PKA enzyme (P < 0.05). Nevertheless, H89, a PKA inhibitor, weakened DHA-induced lipolysis by inhibiting the cAMP/PKA signaling pathway. Furthermore, inhibiting ER stress using 4-PBA also inhibited lipolysis and alleviated DHA-induced activation of the cAMP/PKA signaling pathway, suggesting that ER stress may participate in DHA-induced lipolysis through the activation of the cAMP/PKA signaling pathway. Our data illustrate that DHA supplementation can be a promising nutritional strategy for ameliorating lipid accumulation in grass carp. The present study elucidated the molecular mechanism for DHA-induced lipolysis in grass carp adipocytes and emphasized the importance of ER stress and the cAMP/PKA pathway in DHA-induced lipolysis. These results deepen our understanding of ameliorating lipids deposition in freshwater fish by targeting DHA.

Establishing a model fish for the Neotropical region: The case of the yellowtail tetra Astyanax altiparanae in advanced biotechnology

The use of model organisms is important for basic and applied sciences. Several laboratory species of fishes are used to develop advanced technologies, such as the zebrafish (Danio rerio), the medaka (Oryzias latipes), and loach species (Misgurnus spp.). However, the application of these exotic species in the Neotropical region is limited due to differences in environmental conditions and phylogenetic distances. This situation emphasizes the establishment of a model organism specifically for the Neotropical region with the development of techniques that may be applicable to other Neotropical fish species. In this work, the previous research efforts are described in order to establish the yellowtail tetra Astyanax altiparanae as a model laboratory species for both laboratory and aquaculture purposes. Over the last decade, starting with artificial fertilization, the yellowtail tetra has become a laboratory organism for advanced biotechnology, such as germ cell transplantation, chromosome set manipulation, and other technologies, with applications in aquaculture and conservation of genetic resources. Nowadays, the yellowtail tetra is considered the most advanced fish with respect to fish biotechnology within the Neotropical region. The techniques developed for this species are being used in other related species, especially within the characins class.

The risk assessment of high-fat diet in farmed fish and its mitigation approaches: A review

In the era of intensification of fish farms, the high-fat diet (HFD) has been applied to promote growth and productivity, provide additional energy and substitute partial protein in fish feeds. Certainly, HFD within specific concentrations was found to be beneficial in boosting fish performance throughout a short-term feeding. However, excessive dietary fat levels displayed vast undesirable impacts on growth, feed efficiency, liver function, antioxidant capacity and immune function and finally reduced the economic revenue of cultured fish. Moreover, studies have shown that fish diets containing a high level of fats resulted in increasing lipid accumulation, stimulated endoplasmic reticulum stress and suppressed autophagy in fish liver. Investigations showed that HFD could impair the intestinal barrier of fish via triggering inflammation, metabolic disorders, oxidative stress and microbiota imbalance. Several approaches have been widely used for reducing the undesirable influences of HFD in fish. Dietary manipulation could mitigate the adverse impacts triggered by HFD, and boost growth and productivity via reducing blood lipids profile, attenuating oxidative stress and hepatic lipid deposition and improving mitochondrial activity, immune function and antioxidant activity in fish. As well, dietary feed additives have been shown to decrease hepatic lipogenesis and modulate the inflammatory response in fish. Based on the literature, previous studies indicated that phytochemicals could reduce apoptosis and enhance the immunity of fish fed with HFD. Thus, the present review will explore the potential hazards of HFD on fish species. It will also provide light on the possibility of employing some safe feed additives to mitigate HFD risks in farmed fish.

Distinct responses from triglyceride and cholesterol metabolism in common carp (Cyprinus carpio) upon environmental cadmium exposure

Due to high persistence and bioavailability, Cadmium (Cd) is one of the most prevalent environmental contaminants, posing an elevating threat to the ecosystems. It has been evidenced that high-dose Cd elicits deleterious effects on aquatic organisms, but the potential toxicities of Cd at environmentally relevant concentrations remains underappreciated. In this study, we used common carp to investigate how environmental Cd exposure affects triglyceride (TG) and cholesterol metabolism and underlying mechanisms. The data indicated that Cd resulted in the shift of TG from the liver to blood and the movement of cholesterol in the opposite direction, ultimately giving rise to the storage of crude lipid in liver and muscle, especially hepatic cholesterol retention. Cholesterol, instead of TG, became the principal cause during the progression of hepatic lipid accumulation. Mechanistic investigations at transcriptional and translational levels further substantiated that Cd blocked hepatic biosynthesis of TG and enhanced TG efflux out of the liver and fatty acid β-oxidation, which collectively led to the compromised TG metabolism in the liver and accelerated TG export to the serum. Additionally, strengthened synthesis, retarded export and oxidation of cholesterol detailed the hepatic prominent cholesterol retention. Taken together, our results demonstrated that environmental exposure to Cd perturbed lipid metabolism through triggering distinct responses from hepatic TG and cholesterol homeostasis. These indicated that environmental factors (such as waterborne Cd) could be a potential contributor to the prevalence of non-alcoholic fatty-liver disease in aquaculture and more efforts should be devoted to the ecological risk assessment of pollutants under environmental scenarios.

Dietary nano-selenium alleviated intestinal damage of juvenile grass carp (Ctenopharyngodon idella) induced by high-fat diet: Insight from intestinal morphology, tight junction, inflammation, anti-oxidization and intestinal microbiota

In recent years, high-fat diet (HFD) has been widely applied in aquaculture, which reduces the intestinal health of cultured fish. The current study evaluated the protective effects of nano-selenium (nano-Se) on intestinal health of juvenile grass carp (Ctenopharyngodon idella) fed with HFD. A total of 135 experimental fish were fed with a regular diet (Con), a HFD (HFD) and a HFD containing nano-Se at 0.6 mg/kg (HSe) for 10 weeks. The results showed that dietary nano-Se significantly improved the survival rate and feed efficiency which were reduced by HFD in juvenile grass carp (P < 0.05). Also, nano-Se (0.6 mg/kg) supplement alleviated intestinal damage caused by the HFD, thus maintaining the integrity of the intestine. Moreover, it significantly up-regulated the expression of genes related to tight junction (ZO-1, c laudin-3 and o ccludin), anti-oxidization (GPx4a andGPx4b), and the protein of ZO-1 in the intestine of juvenile grass carp, which were depressed by the HFD (P < 0.05). Furthermore, nano-Se supplementation significantly suppressed the expressions of genes related to the inflammation, including inflammatory cytokines (IL-8, IL-1β, IFN-γ, TNF-α and IL-6), signaling molecules (TLR4, p38 MAPK and NF-κB p65), and protein expression of NF-κB p65 and TNF-α in the intestine of juvenile grass carp which were induced by the HFD (P < 0.05). Besides, dietary nano-Se normalized the intestinal microbiota imbalance of juvenile grass carp caused by the HFD through increasing the abundance of the beneficial bacteria, e.g., Fusobacteria. Finally, dietary nano-Se increased the production of short chain fatty acids (SCFA) in the intestine, especially for butyric acid and caproic acid, which were negatively related to the increase of intestinal permeability and inflammation. In summary, supply of nano-Se (0.6 mg/kg) in HFD could effectively alleviate intestinal injury of juvenile grass carp by improving intestinal barrier function and reducing intestinal inflammation and oxidative stress. These positive effects may be due to the regulation of nano-Se on intestinal microbiota and the subsequently increased beneficial SCFA levels.

Lipidomic Profiling Reveals the Reducing Lipid Accumulation Effect of Dietary Taurine in Groupers (Epinephelus coioides)

A lipidomic analysis was conducted to provide the first detailed overview of lipid molecule profiles in response to dietary lipid and taurine and associations of liver lipid-lowering effects of dietary taurine with lipid molecular species and the positional distributions of fatty acids in the liver of juvenile orange-spotted groupers (Epinephelus coioides). The results indicated that the liver was more sensitive to varied dietary lipid and taurine contents than the muscle with regard to lipid molecules. A total of 131 differential lipid molecules (DLMs) were observed in the liver of groupers when dietary taurine was increased from 0 to 1% at 15% lipid, among which all the up and down-regulated DLMs are phospholipids (PLs) and triglycerides (TGs), respectively. The liver content of TGs containing 18:2n-6 attached at the sn-2 and sn-3 positions on the glycerol backbone increased with increasing dietary lipid from 10 to 15% but decreased with increasing dietary taurine from 0 to 1%. Therefore, dietary taurine can not only reduce lipid accumulation through decreasing the contents of TGs containing 18:2n-6 at the sn-2 and sn-3 positions but also enhance the anti-inflammatory capacity and health status of groupers. This study will also provide a new insight into the function of taurine in farmed fish.

A Study on How Methionine Restriction Decreases the Body's Hepatic and Lipid Deposition in Rice Field Eel (Monopterus albus)

Methionine restriction reduces animal lipid deposition. However, the molecular mechanism underlying how the body reacts to the condition and regulates lipid metabolism remains unknown. In this study, a feeding trial was performed on rice field eel Monopterus albus with six isonitrogenous and isoenergetic feeds that included different levels of methionine (0, 2, 4, 6, 8, and 10 g/kg). Compared with M0 (0 g/kg), the crude lipid and crude protein of M. albus increased markedly in M8 (8 g/kg) (p < 0.05), serum (total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and non-esterified free fatty acids), and hepatic contents (hepatic lipase, apolipoprotein-A, fatty acid synthetase, total cholesterol, triglyceride, and lipoprteinlipase). However, in the serum, very-low-density lipoprotein and hepatic contents (hormone-sensitive triglyceride lipase, Acetyl CoA carboxylase, carnitine palmitoyltransterase, and mirosomal triglygeride transfer protein) decreased markedly in M8 (p < 0.05). The contents of hepatic C18:2n-6, C22:6n-3, and n-3PUFA in the M8 group were significantly higher than those in M0 (p < 0.05), and the contents of lipid droplets in M8 were higher than those in M0. Compared with M0, the hepatic gcn2, eif2α, hsl, mttp, ldlrap, pparα, cpt1, and cpt2 were remarkably downregulated in M8, while srebf2, lpl, moat2, dgat2, hdlbp, srebf1, fas, fads2, me1, pfae, and icdh were markedly upregulated in M8. Moreover, hepatic SREBP1 and FAS protein expression were upregulated significantly in M8 (p < 0.01). In short, methionine restriction decreased the lipid deposition of M. albus, especially for hepatic lipid deposition, and mainly downregulated hepatic fatty acid metabolism. Besides, gcn2 could be activated under methionine restriction.

GC-MS-Based Serum Metabolomic Investigations on the Ameliorative Effects of Polysaccharide from Turpiniae folium in Hyperlipidemia Rats

Hyperlipidemia, a typical metabolic disorder syndrome, can cause various cardiovascular diseases. The polysaccharides were found to have enormous potential in the therapy of hyperlipidemia. This study was aimed at evaluating the ameliorative effects of polysaccharide from Turpiniae folium (TFP) in rats with hyperlipidemia. A serum metabolomic method based on gas chromatography-mass spectrometry (GC-MS) was used to explore the detailed mechanism of TFP in rats with hyperlipidemia. The oxidative stress indicators, biochemical indexes, and inflammatory factors in serum and histopathological changes in the liver were also evaluated after 10-week oral administration of TFP in rats with high-fat diet-induced hyperlipidemia. TFP significantly relieved oxidative stress, inflammation, and liver histopathology and reduced blood lipid levels. Multivariate statistical approaches such as principal component analysis and orthogonal projection to latent structure square-discriminant analysis revealed clear separations of metabolic profiles among the control, HFD, and HFD+TFP groups, indicating a moderating effect of TFP on the metabolic disorders in rats with hyperlipidemia. Seven metabolites in serum, involved in glycine, serine, and threonine metabolism and aminoacyl-tRNA biosynthesis, were selected as potential biomarkers in rats with hyperlipidemia and regulated by TFP administration. It was concluded that TFP had remarkable potential for treating hyperlipidemia. These findings provided evidence for further understanding of the mechanism of action of TFP on hyperlipidemia.

Low Molecular Weight Fucoidan Can Inhibit the Fibrosis of Diabetic Kidneys by Regulating the Kidney Lipid Metabolism

In this study, a diabetic kidney disease model was established by placing the test rats on a high-sugar/high-fat diet combined with streptozotocin induction. Histopathological examination (H&E, Masson, and PASM stain) showed pathological changes in the diabetic rat kidneys, in addition to fibrotic symptoms and collagen deposition. Immunohistochemistry and western blot analyses indicated that the diabetic condition significantly increased the expressions of fibrotic markers including collagen, α-SMA, and fibronectin. The levels of cholesterol, triglyceride, and low-density lipoprotein were also increased in diabetic kidney disease (DKD) rat blood, while the level of high-density lipoprotein was decreased. The results of Oil red O staining experiments indicated that the kidneys of diabetic rats exhibited appreciable fat deposition, with high contents of triglyceride and cholesterol. To inhibit fibrosis and reduce fat deposition, low molecular weight fucoidan (LMWF) may be used. Based on PCR and western blot analyses, LMWF can regulate the expression levels of important lipid metabolism regulators, thereby impeding the development of kidney fibrosis. Through the vitro model, it also be indicated that LMWF could inhibit fibrosis process through regulating lipid metabolism which induced by palmitic acid.

Dietary Supplementation of Astaxanthin Improved the Growth Performance, Antioxidant Ability and Immune Response of Juvenile Largemouth Bass (Micropterus salmoides) Fed High-Fat Diet

High-fat diet (HFD) usually induces oxidative stress and astaxanthin is regarded as an excellent anti-oxidant. An 8-week feeding trial was conducted to investigate the effects of dietary astaxanthin supplementation on growth performance, lipid metabolism, antioxidant ability, and immune response of juvenile largemouth bass (Micropterus salmoides) fed HFD. Four diets were formulated: the control diet (10.87% lipid, C), high-fat diet (18.08% lipid, HF), and HF diet supplemented with 75 and 150 mg kg^-1 astaxanthin (HFA1 and HFA2, respectively). Dietary supplementation of astaxanthin improved the growth of fish fed HFD, also decreased hepatosomatic index and intraperitoneal fat ratio of fish fed HFD, while having no effect on body fat. Malondialdehyde content and superoxide dismutase activity were increased in fish fed HFD, astaxanthin supplementation in HFD decreased the oxidative stress of fish. The supplementation of astaxanthin in HFD also reduced the mRNA levels of Caspase 3, Caspase 9, BAD, and IL15. These results suggested that dietary astaxanthin supplementation in HFD improved the growth performance, antioxidant ability and immune response of largemouth bass.

Effects of Dietary Andrographolide Levels on Growth Performance, Antioxidant Capacity, Intestinal Immune Function and Microbioma of Rice Field Eel (Monopterus Albus)

An eight-week feeding trial was conducted to investigate the effects of dietary andrographolide on the growth performance, antioxidant capacity in the liver, intestinal inflammatory response and microbiota of Monopterus albus. A total of 900 health fish (25.00 ± 0.15 g) were randomly divided into five groups: AD1 (the basal diet) as the control, and AD2, AD3, AD4 and AD5 groups, which were fed the basal diet supplemented with 75, 150, 225 and 300 mg/kg andrographolide, respectively. The results showed that compared with the control group, dietary andrographolide supplementation (1) significantly increased trypsin and lipase activities in the intestine, and increased the weight gain rate but not significantly; (2) significantly increased the levels of glutathione reductase (GR), glutathione (GSH) and glutathione peroxidase (GPx) and the content of in the liver; significantly decreased the contents of reactive oxygen species (ROS) and malondialdehyde (MDA); remarkably upregulated the Nrf2, SOD1, GSTK and GSTO mRNA levels in the liver; downregulated the Keap1 mRNA level; (3) significantly increased the villi length and goblet cell numbers in the intestine, remarkably upregulated the Occludin mRNA level in the intestine, downregulated the Claudin-15 mRNA level; (4) remarkably upregulated the IL-10, TGF-β1 and TGF-β3 mRNA levels in the intestine; downregulated the IL-12β and TLR-3 mRNA levels; (5) significantly decreased the richness and diversity of the intestinal microbioma, increased the percentages of Fusobacteria and Firmicutes and significantly decreased the percentages of Cyanobacteria and Proteobacteria. In conclusion, these results showed that dietary low-dose andrographolide (75 and 150 mg/kg) promoted growth and antioxidant capacity, regulated the intestinal microbioma, enhanced intestinal physical and immune barrier function in rice field eel.

Dietary fat concentrations influence fatty acid assimilation patterns in Atlantic pollock (Pollachius virens)

A key aspect in the use of fatty acids (FA) to estimate predator diets using quantitative FA signature analysis (QFASA) is the ability to account for FA assimilation through the use of calibration coefficients (CC). Here, we tested the assumption that CC are independent of dietary fat concentrations by feeding Atlantic pollock (Pollachius virens) three formulated diets with very similar FA proportions but different fat concentrations (5-9% of diet) for 20 weeks. CC calculated using FA profiles of diet and triacylglycerols in pollock liver were significantly different for the three diets. To test the robustness of diet estimates to these differences, we used the CC set derived from feeding the diet with the lowest fat concentration, published prey FA profiles and realistic diet estimates of pollock to construct 'pseudo-predators'. Application of QFASA to each pseudo-predator using the three sets of CC and the same prey FA profiles resulted in diet estimate biases of twofold for major prey items and approximately fivefold for minor prey items. This work illustrates the importance of incorporating diets with fat concentrations that are similar to natural prey when conducting feeding experiments to calculate CC. This article is part of the theme 'The next horizons for lipids as 'trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.