Search

Based on the concept of nutritional programming in mammals, we tested whether an acute hyperglucidic-hypoproteic stimulus during first feeding could induce long-term changes in nutrient metabolism in rainbow trout. Trout alevins received during the five first days of exogenous feeding either a hyperglucidic (40% gelatinized starch + 20% glucose) and hypoproteic (20%) diet (VLP diet) or a high-protein (60%) glucose-free diet (HP diet, control). Following a common 105- day period on a commercial diet, both groups were then challenged (65 days) with a carbohydrate-rich diet (28%). Short- and long-term effects of the early stimuli were evaluated in terms of metabolic marker gene expressions and intestinal microbiota as initial gut colonisation is essential for regulating the development of the digestive system. In whole alevins (short term), diet VLP relative to HP rapidly increased gene expressions of glycolytic enzymes, while those involved in gluconeogenesis and amino acid catabolism decreased. However, none of these genes showed persistent molecular adaptation in the liver of challenged juveniles (long term). By contrast, muscle of challenged juveniles subjected previously to the VLP stimulus displayed downregulated expression of markers of glycolysis and glucose transport (not seen in the short term). These fish also had higher plasma glucose (9 h postprandial), suggesting impaired glucose homeostasis induced by the early stimulus. The early stimulus did not modify the expression of the analysed metabolism-related microRNAs, but had short- and long-term effects on intestinal fungi (not bacteria) profiles. In summary, our data show that a short hyperglucidic-hypoproteic stimulus during early life may have a long-term influence on muscle glucose metabolism and intestinal microbiota in trout. [ABSTRACT FROM AUTHOR]

Utilizing rainbow trout (Oncorhynchus mykiss) as a known model of a "glucose- intolerant" and poor dietary glucose user, we assessed glucose utilization in fish chronically receiving two molecules able to improve glucose homeostasis: insulin and metformin. Our objectives were to assess the ability of rainbow trout to deal with a glucose load and to improve glucose utilization in fish receiving a chronic administration of insulin plus metformin treatments. Fish received (implanted miniosmotic pumps) saline, insulin, metformin, and insulin plus met form in solution for 4 days and then were subjected to a glucose challenge (intraperitoneal injection) to study glucose homeostasis, analyzing plasma glycemia, mRNA levels of glucose metabolism related proteins, insulin signaling, and glycogen levels in liver and muscle. Control fish received a saline pump implantation and saline intraperitoneal injection. We found no evidence that the "glucose intolerance" in this species could be linked to any of the molecular markers of metabolism in the tissues analyzed. By contrast, very interestingly, we show for the first time, that metformin is not only unable to improve glucose homeostasis in trout, but, in fact, its counter acts the effects of insulin, creating an "insulin resistance," especially in the muscle. These results make trout an attractive original model to study both insulin and metformin effect on biological systems. [ABSTRACT FROM AUTHOR]

The origin for the poor glucose utilization in carnivorous fish species fed high carbohydrate diets remains under debate. In the present study, we have fed rainbow trout a diet containing 30% carbohydrate for 1 or 5 days. In both cases, fish were implanted with mini-osmotic pumps releasing 0.7 i.u. kg-1 day-1 bovine insulin, and mRNA transcripts and the protein phosphorylation status of proteins controlling glycemia and glucose-related metabolism were studied in fish killed 6 h after the last meal. We demonstrate that when the exposure occurs over a short term (30h), insulin exerts beneficial actions on trout glucose homeostasis, including a lowered glycemia and increased hepatic lipogenic and glycogenic potentials. However, when trout were fed for 5 days, these beneficial actions of insulin infusion were no longer observed. Thus, the increased lipogenic potential observed after one single meal was not present, and this together with the increased glycogenesis and the decreased glucose exported to the blood from the liver explains the lack of hypoglycemic action of insulin. The fact that insulin improved glucose homeostasis when administrated over a short time period implies that endogenous insulin secretion is inadequate in trout to deal with this amount of dietary carbohydrates. Moreover, the fact that a longer exposure to insulin resulted in a reduced response indicates that the rainbow trout is sensitive to insulin, re-enforcing the hypothesis that the hyperglycemia observed following a high carbohydrate meal is an insulin secretion issue rather an insulin action issue. [ABSTRACT FROM AUTHOR]

Mandarin fish (Siniperca chuatsi) can adapt to artificial diets, with the improvement of domestication level. However, the effects of artificial diets on the muscle health of fish are unclear. In this study, 480 homogenous-sized mandarin fish (initial weight of 25.1 ± 0.1 g) were randomly divided into two groups and fed with artificial diets or live prey fish for eight weeks. The transcriptome sequencing analysis identified that artificial diets primarily affected glucose metabolism, lipid metabolism, and immune system in the muscle. Furthermore, artificial diets induced excessive glycogen accumulation in the muscle by increasing the mRNA expression of gluconeogenesis-related genes and decreasing the mRNA expression of glycolysis-related genes. Meanwhile, artificial diets significantly increased triglyceride accumulation in the muscle by upregulating the activity of fatty acid synthetase and the mRNA expression of lipid synthesis-related genes, including srebp1, fas, and plin2. Artificial diets significantly increased the level of malondialdehyde, leading to oxidative stress in the muscle. Besides, artificial diets also upregulated the mRNA expression of pro-inflammation cytokines, including il-1β, ifn-γ, and tnfα. In conclusion, artificial diets disrupted glucose and lipid metabolism and induced oxidative stress and inflammation in the muscle of mandarin fish. [ABSTRACT FROM AUTHOR]

Both in nature and in aquaculture, fish may experience periods of food scarcity or hunger. The metabolic regulation of fish when nutritional state changes is a complex process that involves many factors. To study glucose metabolism adaptability during fasting and re-feeding in the black carp (Mylopharyngodon piceus), we measured changes in some biochemical indicators related to glucose metabolism. Five fish were sampled on days 0, 1, 3, 5, and 10 of fasting (F, S1, S3, S5, and S10, respectively) and days 1, 3, and 5 of re-feeding (RF1, RF3, and RF5, respectively). The serum glucose concentration decreased significantly at S1, reached the lowest point at S10, and increased significantly at RF1 (P < 0.05). The concentration of liver glycogen decreased significantly at S1 and reached the lowest level at S3, whereas the muscle glycogen level decreased significantly at S5 and reached the lowest value at S10 (P < 0.05). Both liver and muscle glycogen levels returned to the pre-fasting level at RF5 (P < 0.05). Regarding glycolysis, the concentrations of pyruvate kinase (PK) and hexokinase (HK) decreased significantly at S5 and increased significantly at RF5 and RF1, respectively (P < 0.05). The concentrations of glucokinase (GCK) and insulin decreased significantly at S1 and increased significantly at RF1 and RF3, respectively (P < 0.05). The mRNA expression levels of liver GCK and glucose transporter 2 (GLUT2) decreased significantly at S1 and increased significantly at RF1 and RF5, respectively (P < 0.05). As for gluconeogenesis, the concentration of glucose-6-phosphatase (G6PC) increased significantly at S1 and decreased significantly at RF1 (P < 0.05). The concentrations of glucagon and glucocorticoid (GC) increased significantly at S3 and significantly decreased at RF1 and RF5, respectively (P < 0.05). The mRNA expression levels of liver G6PC and phosphoenolpyruvate carboxykinase (PEPCK) increased significantly at S3 and S1, and both decreased significantly at RF1 (P < 0.05). These results indicate that coordination between glycolysis and gluconeogenesis might be crucial for glucose homeostasis during fasting and re-feeding in the black carp. [ABSTRACT FROM AUTHOR]

Copyright of South China Fisheries Science is the property of South China Fisheries Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mammalian target of rapamycin (mTOR) has been shown to play a central role in regulating cell growth and metabolism. However, little is known about the function of mTOR in nutrient metabolism in bivalve mollusks. In this study, the role of mTOR in the regulation of nutrient metabolism was investigated in Sinonovacula constricta. First, the activation of mTOR was assayed after starvation and refeeding. Afterwards, the role of mTOR in the regulation of nutrient metabolism was investigated using an activator (MHY1485) or inhibitor (rapamycin) of mTOR. The open reading frame of the S. constricta mTOR is 7416 bp in length and encodes a polypeptide consisting of 2471 amino acids. The mTOR amino acid sequence of S. constricta was highly conserved when compared with other species and had a close evolutionary relationship with the TOR proteins of Crassostrea gigas and Lingula anatine. mTOR was expressed in the intestine, exhalent siphon, labial palppus, muscle, inhalent siphon, gill, mantle, digestive land, and gonad tissue of S. constricta, with the highest expression in muscle. During starvation, the level of phosphorylated mTOR protein was relatively low, and the ratio of LC3II/LC3I protein and the AMPKα mRNA level significantly increased with the increase in starvation time. After feeding, the level of phosphorylated mTOR protein increased from 0.13 to 0.56, and the ratio of LC3II/I protein and AMPKα mRNA level decreased from 1.17 to 0.38. MHY1485 significantly increased the level of phosphorylated 4E-BP1 and significantly decreased the ratio of LC3II/I proteins. Furthermore, MHY1485 significantly increased the mRNA level of the glucose metabolism-related gene glucokinase (GK), significantly decreased the mRNA expression of the G6P gene, and significantly increased the mRNA expression of the lipid synthesis-related genes sterol-regulatory element-binding protein (SREBP) and stearoyl-CoA desaturase (SCD). Rapamycin significantly reduced the level of phosphorylated 4E-BP1 and the mRNA expression of mTOR, and the expression level of phosphorylated 4EBP1 decreased from 0.97 to 0.28. Meanwhile, it also significantly reduced the mRNA expression of glucose metabolism-related genes GK, pyruvate kinase (PK), glucose transporter 1 (GLUT1), and G6P, as well as lipid synthesis-related genes SCD and acetyl-CoA carboxylase (ACC). These results indicate a conserved role of mTOR in regulating nutritional metabolism, including glucose metabolism, lipid synthesis, and autophagy in S. constricta. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to evaluate the application of common carbohydrate sources, cornstarch (CS), wheat starch (WS), and wheat flour (WF), to different gibel carp genotypes, Dongting, CASIII, and CASV. The results of the growth and physical responses were analysed by data visualization and unsupervised machine learning. As revealed by a self-organizing map (SOM) and the cluster of growth and biochemical indicators, CASV had superior growth and feed utilization and better regulation of postprandial glucose, followed by CASIII, while Dongting showed a high level of plasma glucose with poor growth performance. CS, WS, and WF were differently utilized by the gibel carp, and WF was associated with greater zootechnical performance based on higher specific growth rate (SGR), feed efficiency (FE), protein retention efficiency (PRE), and lipid retention efficiency (LRE), induced hepatic lipogenesis, increased liver lipids, and enhanced muscle glycogen. Spearman's correlation analysis of the physiological responses indicated that plasma glucose had a significantly negative correlation with growth, feed utilization, glycogen storage, and plasma cholesterol level, and it was positively related to liver fat content in gibel carp. Transcriptional variabilities were observed: CASIII showed increased expression of pklr, which is involved in hepatic glycolysis, and pck and g6p, which are involved in gluconeogenesis. Interestingly, Dongting showed upregulation of genes involved in glycolysis and fatty acid oxidation in muscle. Furthermore, there were numerous interactions between carbohydrate sources and strains for growth, metabolites, and transcriptional control, confirming the existence of genetic polymorphisms in carbohydrate use in gibel carp. Globally, CASV showed relatively better growth and carbohydrate utilization, and wheat flour seemed to be more efficiently utilized by gibel carp. [ABSTRACT FROM AUTHOR]

Glucose transporter 4 (GLUT4) is comprehensively investigated in mammals, while the comparative research of GLUT4 in common carp is deficient. To investigate the function of GLUT4, carp glut4 was first isolated. The open reading frame of carp glut4 was 1518 bp in length, encoding 505 amino acids. A high‐sequence homology was identified in carp and teleost, and the phylogenetic tree displayed that the carp GLUT4 was clustered with the teleost. A high level of glut4 mRNA was analysed in fat, red muscle and white muscle. After fasting treatment, glut4 mRNA expression was increased significantly in muscle. In the oral glucose tolerance test experiment, glut4 mRNA was also significantly elevated in muscle, gut and fat. Furthermore, intraperitoneal injection of insulin resulted in the upregulation of glut4 gene expression significantly in white muscle, gut and fat. On the contrary, the glut4 mRNA level in the white muscle, gut and fat was markedly downregulated after glucagon injection. These results suggest that GLUT4 might play important roles in food intake and could be regulated by nutrient condition, insulin and glucagon in common carp. Our study is the first to report on GLUT4 in common carp. These data provide a basis for further study on fish GLUT4. [ABSTRACT FROM AUTHOR]

This study was performed to evaluate the effects of dietary distinct protein to starch ratios on the growth, feed utilization, blood biochemistry, hepatic glucose metabolism and hepatocyte apoptosis of Nile tilapia Oreochromis niloticus. Three iso-lipidic (ca 6.56%) diets were formulated with elevated corn starch levels at the cost of protein provision, being designated as diets P40S5 (40.4% protein and 4.62% starch), P30S25 (30.4% protein and 24.2% starch) and P20S50 (19.9% protein and 48.6% starch). Tilapia juveniles (initial mean body weight, 32.0 g/fish) were assigned to 12 rectangular tanks (250 L each) with 20 fish per tank and fed the experimental diets to apparent satiation for 8 weeks. The results showed that either excess (40%) or insufficient (20%) amount of dietary protein impaired the growth of tilapia. Excess dietary protein led to unsatisfactory protein catabolism (lower protein efficiency ratio and protein productive value, and higher mRNA levels of hepatic glutamic-pyruvic transaminase 1 and glutamic-oxaloacetic transaminase paralogs), while insufficient amount of protein resulted in lower whole-body protein percentage. An increase in dietary starch from 5% or 25% to 50% was associated with enhanced lipid and glycogen storages in the liver of tilapia. Consistently, dietary starch reception up to 50% upregulated the expression of hepatic representative genes involved with glycolysis (glucokinase and phosphofructokinase muscle type a) and lipogenesis (acetyl-CoA carboxylase α and fatty acid synthase) while downregulated the expression of the gluconeogenic glucose-6-phosphatase catalytic subunit paralogs. TUNEL staining suggested that stronger apoptosis signal was recorded at the bile duct epithelium of the P20S50 fish. Concomitantly, plasma bile acid level nearly doubled, and an incidence (50%) of 'green liver' was observed in this treatment as compared with the P40S5 and P30S25 fish, indicating that bile acid metabolism disorder might be induced. Though plasma glucose (4.66-5.11 mmol/L) was not responsive to different treatments, advanced glycation end-products accumulated in the blood of the P20S50 fish, suggesting that 50% starch reception was probably associated with the progression of diabetes-associated pathologies. The overall results in this study suggested that tilapia might possess capability to tolerate dietary corn starch level up to 50% in a short-term exposure, whereas a long-term exposure might induce detrimental effects on liver functions. [ABSTRACT FROM AUTHOR]

It was previously shown that the influence of high‐energy diets on growth and flesh quality of grass carp was closely related to energy resource. The mechanisms were explored in this study by investigating the hepatic lipid and glucose metabolism of grass carp. Juvenile grass carp (Ctenopharyngodon idella) with initial body weight (55.0 ± 2.5) g were fed with four purified diets for 11 weeks, with four replicates per diet and 20 fish per replicate. Three high‐energy diets with high level of carbohydrate, fat and protein were prepared, and their gross energy was 11% higher than that of control diet. Results showed that the highest contents of hepatic crude fat, total saturated fatty acids, n‐6 unsaturated fatty acids and glycogen, as well as the highest grade of hepatocyte steatosis were observed in grass carp fed the high‐carbohydrate diet. Data on hepatic mRNA expression indicated that the high‐carbohydrate diet increased the genes expression including pk, gck, g6pd, fas and acc‐1, while the high‐fat diet significantly increased the genes expression including pk, gck, fbp, pck, lpl and hsl. The high‐fat and high‐carbohydrate diets activated hepatic AMPK/ACC pathway, whereas inhibited TOR/SREBP‐1 pathway. In conclusion, the high‐carbohydrate diet had a stronger effect on the hepatic lipid accumulation than the high‐fat diet in grass carp. The acceleration of lipolysis, glycolysis and gluconeogenesis in liver improved the utilization of the high‐fat diet in grass carp. Besides, the high‐carbohydrate diet can promote hepatic glycolysis and pentose phosphate shunt and inhibit gluconeogenesis in grass carp. [ABSTRACT FROM AUTHOR]

Glucose transporter 2 (glut2) has been studied in mammals, aves, and several fish, while the comparative studies of glut2 in common carp are still lacking. In this study, glut2 was firstly isolated and characterized from the liver of common carp. The full-length cDNA of glut2 was 2351 bp with an open reading frame (ORF) of 1512 bp, encoding 503 amino acids. Alignment of glut2 amino acid sequences from different species revealed that common carp glut2 showed higher sequence identity with teleosts, and lower homology with mammals and amphibians. Tissue distribution demonstrated that glut2 mRNA level was mainly expressed in liver, foregut, and midgut. To investigate the actions of glut2 on glucose metabolism, the level of glut2 mRNA was detected after intraperitoneal injection of glucose, human insulin and glucagon (100 ng/g), respectively. Following glucose administration, glut2 gene expression was significantly upregulated at 3 h in the foregut. However, no change was found in hepatic glut2 mRNA level, indicating that glut2 may have a role in intestinal glucose uptake rather than in the liver. Following insulin treatment, the expression of glut2 was markedly downregulated at 3 h and 6 h in the liver, and at 3 h in the foregut, respectively. Furthermore, glut2 mRNA expression was unaffected by glucagon injection in the liver and foregut. These results suggested that the expression of glut2 regulated by pancreatic hormones was different. Taken together, our studies firstly revealed the structure of the glut2 gene and its potential functions in glucose metabolism of common carp. [ABSTRACT FROM AUTHOR]

A 12‐week feeding trial was conducted to evaluate the effects of nicotinamide on the growth performance, glucose and lipid metabolism of blunt snout bream fed high‐carbohydrate diets. Fish were randomly fed four diets including two dietary carbohydrate levels (300 and 430 g/kg, deriving from corn starch) and two nicotinamide levels (0 and 31.0 mg/kg). Microcrystalline cellulose was incorporated to compensate for the carbohydrate levels required. High‐carbohydrate levels significantly (p <.05) increased the hepatosomatic index, intraperitoneal fat percentage, the contents of whole‐body lipid and tissues (including liver, muscle and adipose tissue) glycogen and lipid, plasma levels of glucose, glycated serum protein, advanced glycation end products, triglyceride, pyruvate and lactic acid, as well as the hepatic transcriptions of peroxisome proliferator‐activated receptor γ (PPARγ), PPARα, glucose transporter 2 (GLUT2), glucokinase (GK), pyruvate kinase (PK), glycogen synthase (GS), glucose‐6‐phosphate dehydrogenase, sterol regulatory element‐binding protein‐1, fatty acid synthase (FAS), carnitine palmitoyl transferase I (CPTI), acetyl‐CoA carboxylase α, whereas the opposite was found for hepatic nicotinamide adenine dinucleotide (NAD+), nicotinamide adenine dinucleotide phosphate (NADH) and hepatic sirtuin‐1 (SIRT1) protein level and the transcriptions of SIRT1, forkhead transcription factor 1(FOXO1), phosphoenolpyruvate carboxykinase, glucose‐6‐phosphatase (G6pase) and acyl‐CoA oxidase (p <.05). Additionally, nicotinamide supplementation significantly (p <.05) increased whole‐body lipid and tissues glycogen contents, hepatic NAD+ content and the NAD+/NADH ratio, hepatic SIRT1 protein level and the transcriptions of SIRT1 coactivators (PPARγ coactivator‐1α, FOXO1 PPARα), GLUT2, GK, PK, G6pase, GS and CPTI, while the opposite was found for the remaining indicators. Furthermore, a significant (p <.05) interaction between dietary carbohydrate levels and nicotinamide was also observed in most parameters aforementioned. Overall, nicotinamide benefits the glucose and lipid metabolism of Megalobrama amblycephala fed high‐carbohydrate diets by mediating the transcriptions of SIRT1 and glucose and lipid metabolism‐related genes as well as stimulating glucose transportation, glycolysis, glycogenesis, fatty acid oxidation, while depressing both lipogenesis and gluconeogenesis. [ABSTRACT FROM AUTHOR]

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate to lipid (CHO:L) ratios on growth performance, muscle fatty acid composition, and intermediary metabolism in juvenile black seabream (Acanthopagrus schlegelii). Five isonitrogenous and isoenergetic diets (48.0% crude protein and 18.0 MJ kg–1 gross energy) were formulated to contain different CHO:L ratios ranging from 0.33 to 3.75. Triplicate groups of 20 fish averaging 0.51 ± 0.01 g were fed with experimental diets twice daily to apparent satiation. The results indicated that final body weight (FBW), percentage weight gain (PWG), specific growth rate (SGR), and protein efficiency ratio (PER) were significantly influenced by the dietary CHO:L ratios (p < 0.05). The highest FBW, PWG, and SGR were observed in fish fed the diet with a CHO:L ratio of 1.36 (p < 0.05). A two-slope broken-line regression analysis based on PWG indicated that the optimal dietary CHO:L is 1.08. Lipid content in the whole body decreased, and glycogen concentration in the liver increased with the increase of dietary CHO:L ratios from 0.33 to 3.75 (p < 0.05). Moreover, there was a positive correlation between muscle fatty acid composition and dietary fatty acid composition. The relative expression levels of genes involved in glucose metabolism, such as gk , pepck , and glut2 were upregulated by increasing the dietary CHO:L ratio. Also, the mRNA expression level of genes related to lipid synthesis, such as fas and acc α were significantly upregulated with dietary CHO:L ratios increasing from 0.33 to 3.75. The highest expression of genes involved in fatty acid β-oxidation, such as cpt1 and acox1 , were observed in fish fed the 1.36 CHO:L ratio diet. The gene expression of Δ6 fatty acyl desaturase (fads2) in the liver significantly increased with increase of dietary CHO:L ratios from 0.33 to 3.75. Fish fed the diet with CHO:L ratios of 2.26 and 3.75 had lower expression levels of elovl5 than those fed the other diets. These results demonstrate that dietary optimal CHO:L ratios could improve PWG and SGR but also influence expression of genes involved in glucose and lipid metabolism. Based on the overall results, the optimal dietary CHO:L ratio is 1.08 for black seabream. [ABSTRACT FROM AUTHOR]

Sustainable aquaculture production requires a greater reduction in the use of marine-derived ingredients, and one of the most promising solutions today is the augmentation in the proportion of digestible carbohydrates in aquafeed. This challenge is particularly difficult for high trophic level teleost fish as they are considered to be glucose-intolerant (growth delay and persistent postprandial hyperglycemia observed in juveniles fed a diet containing more than 20% of carbohydrates). It was previously suggested that broodstock could potentially use carbohydrates more efficiently than juveniles, probably due to important metabolic changes that occur during gametogenesis. To investigate this hypothesis, 2-year old male and female rainbow trout (Oncorhynchus mykiss) were either fed a diet containing no carbohydrates (NC) or a 35%-carbohydrate diet (HC) for an entire reproductive cycle. Zootechnical parameters as well as the activities of enzymes involved in carbohydrate metabolism were measured in livers and gonads. Fish were then reproduced to investigate the effects of such a diet on reproductive performance. Broodstock consumed the HC diet, and in contrast to what is commonly observed in juveniles, they were able to grow normally and they did not display postprandial hyperglycemia. The modulation of their hepatic metabolism, with an augmentation of the glycogenesis, the pentose phosphate pathway and a possible better regulation of gluconeogenesis, may explain their improved ability to use dietary carbohydrates. Although the HC diet did induce precocious maturation, the reproductive performance of fish was not affected, confirming that broodstock are able to reproduce when fed a low-protein high-carbohydrate diet. In conclusion, this exploratory work has shown that broodstock are able to use a diet containing digestible carbohydrates as high as 35% and can then grow and reproduce normally over an entire reproductive cycle for females and at least at the beginning of the cycle for males. These results are highly promising and suggest that dietary carbohydrates can at least partially replace proteins in broodstock aquafeed. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore for the first time in omnivorous fish the concept of nutritional programming. A nutritional stimulus was accomplished by microinjecting 2 M glucose into yolk reserves during the alevin stage in Nile tilapia (Oreochromis niloticus). At the molecular level in fry, at 1 week post-injection, glucose stimuli were associated with the up-regulation of genes involved in glycolysis (pklr , hk1 , hk2 , and pkma), glucose transport (glut4) pathways and down-regulation of genes related to gluconeogenesis (g6pca1 , g6pca2 , and pck1) and amino acid catabolism (asat , alat) (P < 0.05), demonstrating that the larvae well received the glucose stimulus at a molecular level. Moreover, 20 weeks after glucose injection, early glucose stimuli were always linked to permanent effects in juvenile fish, as reflected by a higher level of glycolytic enzymes [ gck , hk1 and hk2 at both mRNA and enzymatic levels and pyruvate kinase (PK) activity]. Finally, the effects of the glucose stimulus history were also examined in fish fed with two different dietary carbohydrate/protein levels (medium-carbohydrate diet, CHO-M; high-carbohydrate diet, CHO-H) in juvenile fish (during weeks 20–24). As expected, the CHO-H diet induced the expression of glycolytic and lipogenic genes (gck , pklr , hk1 , hk2 , fpkma, fasn , and g6pd) and suppressed the expression of gluconeogenic and amino acid catabolism genes (g6pca1 , pck1 , pck2 , asat , alat , and gdh). Nevertheless, the early glucose stimulus led to persistent up-regulation of glycolytic enzymes (gck , pklr , hk1 , and hk2) at both the mRNA and enzyme activity levels and glucose transporter glut4 as well as lower gluconeogenic pck1 gene expression (P < 0.05). More interestingly, the early glucose stimulus was associated with a better growth performance of juvenile fish irrespective of the diets. These permanent changes were associated with DNA hypomethylation in the liver and muscles, suggesting the existence of epigenetic mechanisms at the origin of programming. In conclusion, for the first time in tilapia, early glucose stimuli were found to be clearly associated with a positive metabolic programming effect later in life, improving the growth performance of the fish. [ABSTRACT FROM AUTHOR]

Japanese flounder juveniles (initial body weight: 7.12 ± 0.02 g) were fed three diets containing 0, 120 and 200 g/kg of carbohydrates (C0, C120 and C200, respectively) for 10 weeks. Results showed that higher dietary carbohydrate intake enabled further deposition of glycogen and lipids in liver and muscle. The mRNA levels of glucokinase (gck), phosphofructokinase (pfkl) and hexokinase (HK) activity involved in glycolysis were significantly up‐regulated in C120 (p <.05) but showed no further up‐regulation except for gck in C200. Besides, the gluconeogenic phosphoenolpyruvate carboxykinase 1 (pck1) mRNA levels were down‐regulated significantly in fish fed the C120 (p <.05). However, further increase in dietary carbohydrate levels increased the mRNA levels and activities of enzymes involved in gluconeogenesis and lipolysis (p <.05). Additionally, plasma glucose remained unchanged in C120 (p >.05) but significantly increased in C200 group (p <.05). In conclusion, Japanese flounder was able to use carbohydrates efficiently through regulation of glucose and lipid metabolism when dietary carbohydrate was not higher than 120 g/kg, while 200 g/kg of dietary carbohydrate caused the deregulation of glucose homoeostasis. [ABSTRACT FROM AUTHOR]

A 10‐week feeding trial was conducted to evaluate the growth performance, glucose transport and metabolism of Chinese soft‐shelled turtles (Pelodiscus sinensis) exposure to graded levels of dietary starch (0.52%, 7.43%, 14.74%, 22.99% and 31.38%). The 360 turtles (initial body weight, 12.94 ± 0.50 g) with 12 replicates were randomly assigned to five experimental diets. The highest weight gain and specific growth rate (SGR) were observed in 7.43% group and the lowest in 31.38% group. The protein efficiency ratio, whole‐body lipid contents, hepatic glycogen contents and the 4‐hr postprandial plasma glucose levels were significantly increased with the increment of starch levels (p <.05). In contrast, the daily feed intake and feed conversion ration were significantly declined (p <.05). The mRNA levels of glucose transporter 2, glucokinase, pyruvate kinase, malic enzyme and acetyl‐CoA carboxylase alpha genes in the liver significantly increased as the increase in starch levels at 4‐hr and 24‐hr post feeding (p <.05). No significant differences were observed in the expression of gluconeogenesis genes at each time point (p >.05). These results suggested that dietary addition of starch up‐regulated hepatic glycolysis, glycogenesis and lipogenesis genes expression, but the deficient response of gluconeogenesis to dietary starch might be part of the causes limited the starch utilization. Based on the secondary polynomial regression of SGR, y = −0.0011x2 + 0.028x + 1.63 (R2 = 0.9292), the 12.73% inclusion level of dietary starch was recommended in juvenile turtles. [ABSTRACT FROM AUTHOR]

Juvenile cobia (Rachycentron canadum), a carnivorous fish, was chosen to examine the effects of methionine (Met) supplementation of low fishmeal diets on growth and the expression of key genes related to hepatic lipogenesis and glucose metabolism. Seven isonitrogenous and isolipidic diets were formulated to contain 7.2, 9.0, 10.0, 12.4, 14.1, 16.3 and 18.6 g/kg dietary Met levels. Healthy cobia (initial average weight ± SE = 9.79 ± 0.04 g) were randomly assigned into seven groups in triplicate with 40 individuals per sea cage for 8 weeks. The results showed that the weight gain rate (WGR) of fish increased as the dietary Met was increased up to 12.4 g/kg and then decreased. The expression of insulin‐like growth factor‐I (IGF‐I) and target of rapamycin (TOR) genes was inhibited by the Met‐deficient diets. The mRNA levels of fatty acid synthase (FAS) and sterol regulatory element‐binding protein‐1 (SREBP1) genes increased with increasing dietary Met until 12.4 g/kg after which the former remained constant, whereas the latter decreased from 12.4 to 18.6 g/kg Met. The mRNA levels of pyruvate kinase (PK) increased as the dietary Met levels increased, reaching a peak at 12.4 g/kg, and then decreased with further increases in Met. However, the mRNA levels of phosphoenolpyruvate carboxykinase (PEPCK) decreased as the dietary Met was increased up to 12.4 g/kg and then remained constant from 12.4 to 18.6 g/kg Met. In conclusion, based on the straight broken‐line analysis of WGR against dietary Met levels, the optimal dietary Met requirement for juvenile cobia was estimated to be 12.4 g/kg (26.9 g/kg dietary protein). A diet with the optimal level of Met induces fish growth and is associated with increased IGF‐I and TOR. [ABSTRACT FROM AUTHOR]

Fish are poor users of dietary carbohydrates and considered to be glucose intolerant, and activating AMP‐activated protein kinase (AMPK) by 5‐aminoimidazole‐4‐carboxamide ribonucleoside (AICAR) has been shown to stimulate glucose uptake and utilization in skeletal muscle cells of rainbow trout. However, the effects of activating AMPK by dietary AICAR in the piscine model remain largely unexplored. In the present study, grass carp were fed purified diets including AICAR at a level of 0 or 200 mg/kg diet to chronically activate AMPK for 8 weeks, and the dietary effects on phenotypic and molecular responses related to glucose and lipid metabolism were examined. The results showed that activating AMPK by dietary AICAR significantly reduced fish growth performance, serum glucose and triacylglycerol contents, and liver lipid contents, while it increased hepatic glycogen contents (p < 0.05). The survival was not influenced by AICAR treatment (p > 0.05). The results of AMPK signalling pathway in both the liver and muscle show that dietary AICAR increased the phosphorylation of AMPKα and acetyl‐CoA carboxylase (ACC; p < 0.05), while inhibiting the phosphorylation of sterol regulatory element‐binding transcription factor‐1(SREBP‐1) and target of rapamycin (p < 0.05). The activation of AMPK reduced the mRNA expression of lipogenesis enzymes in the liver and muscle (p < 0.05) and increased mRNA expression of gluconeogenesis enzymes in the liver and glycolysis enzymes in the heart (p < 0.05). Our results demonstrate that activating AMPK by AICAR reduces serum glucose and inhibits activities of ACC and SREBP‐1 to reduce lipogenesis in the liver and muscle, and AMPK could be used as an active target for its metabolic syndromes of grass carp. [ABSTRACT FROM AUTHOR]

Background: Rainbow trout is a "glucose-intolerant" carnivorous species. Using the metabolic programming strategy, we used early nutritional stimuli in order to modify carbohydrate utilization in trout juveniles. Method: Fish were fed two diets during the first feeding, namely HP (no carbohydrate / high protein) diet and LP (high carbohydrate / low protein) diet. HP diet was used as the control diet and LP diet as an early stimulus diet. We also used another early stimulus with fish fed HP diet every other day during the first feeding (HP restriction feeding - HPR). After the first-feeding stage (4 weeks), all fish were subsequently subjected to a growth trial with a commercial diet followed by a challenge test with the LP diet (11 weeks). At the end of the first feeding stimulus and of the challenge test, we investigated growth performance, glucose metabolism-related parameters and global DNA CmCGG methylation in trout. Results: LP and HPR dietary stimuli have been a success as shown by the direct modifications of growth performance and mRNA levels for glucose metabolism-related genes at the end of first feeding compared to alevins fed the HP diet. At the end of the challenge trial, no variation in growth performance and hepatic metabolism of LP-history and HPR-history in trout juveniles were observed. However, in muscle of trout juvenile subjected to LP diet at the first feeding, we found an up-regulation of mRNA levels of some glucose metabolism (glucose transport and glycolysis)-related genes and an increase of activities of important glycolysis-related enzymes (hexokinase, phosphofructokinase and pyruvate kinase). These observations are associated with a decrease in the content of glycogen compared to fish fed the HP diet. Moreover, global CmCGG DNA methylation in the muscle of fish with LP history was significantly lower than those fed the HP diet. Conclusion: Dietary LP stimulus at first feeding could permanently modify glucose metabolism and global CmCGG DNA methylation level in muscle of trout juveniles, showing that the first feeding stage is efficient for programming the glucose metabolism in fish. [ABSTRACT FROM AUTHOR]

Juvenile rainbow trout develop social hierarchies when held in dyads, and the development of socially subordinate (SS) and social dominance (SD) phenotypes in this context has been linked to specific changes in the hepatic energy metabolism of all major macronutrients. Following our recently reported finding that transcript abundance of drosha, a key component of the microRNA (miRNA) biogenesis pathway, is increased in paired juvenile rainbow trout irrespective of social status compared to socially isolated (SI) controls, we here determined global changes of the hepatic miRNA pathway genes in detail at the transcript and protein level. Both socially SD and SS rainbow trout exhibited increased Ago2 protein abundance compared to SI rainbow trout, suggesting that hepatic miRNA function is increased in rainbow trout maintained in dyads. Given the well-described differences in hepatic intermediary metabolism between socially SD and SS rainbow trout, and the important role of miRNAs in the posttranscriptional regulation of metabolic pathways, we also identified changes in hepatic miRNA abundance between socially SS and SD rainbow trout using small RNA next generation sequencing. We identified a total of 24 differentially regulated miRNAs, with 15 miRNAs that exhibited increased expression, and 9 miRNAs that exhibited decreased expression in the liver of socially SS trout compared to socially SD trout. To identify potential miRNA-dependent posttranscriptional regulatory pathways important for social status-dependent regulation of hepatic metabolism in rainbow trout, we used an in silico miRNA target prediction and pathway enrichment approach. We identified enrichment for pathways related to metabolism of carbohydrates, lipids and proteins in addition to organelle-specific processes involved in energy metabolism, especially mitochondrial fusion and fission. Select predicted miRNA-mRNA target pairs within these categories were quantitatively analyzed by real-time RT-PCR to validate candidates for future studies that will probe the functional metabolic roles of specific hepatic miRNAs in the development of socially SD and SS metabolic phenotypes. [ABSTRACT FROM AUTHOR]

This experiment was conducted to study the effects of dietary carbohydrate on glucose metabolism in gibel carp (Carassius gibelio) as well to investigate if different clones had different responses to carbohydrate intake. Unselected Dongting strain (DT strain), selected gibel carp "CAS III" (A strain) and gibel carp "CAS V" (F strain) were fed with no corn starch diet (0C), 30% corn starch diet (30C) and 45% corn starch diet (45C) for 8 weeks. The results showed that selected F strain showed higher growth performance. F strain and A strain showed better control on postprandial glucose regulation by increasing plasma triglyceride, plasma cholesterol, liver and muscle glycogen contents and also enhancing glycolysis and restraining gluconeogenesis. DT strain had higher body lipid and lipid utilization. In conclusion, gibel carp could tolerate 45% dietary carbohydrate and F strain showed better growth by increasing glycolysis while decreasing glycogenesis. [ABSTRACT FROM AUTHOR]

The study reported here is the first to systematically investigate the postprandial change in glucose metabolism in the adipose tissue (AT) of an omnivorous fish. Sub-adult Genetically Improved Farmed Tilapia (GIFT) Oreochromis niloticus were sampled at 0, 1, 3, 8 and 24 h after feeding (HAF), and the time course of changes in glucose transport and glycolipid metabolism at the transcript level were analyzed in the AT. The plasma glucose level increased between 1 and 8 HAF, and the expression of glucose transporter 1a (glut1a) and glut4 in the AT were stimulated at the same time. Concomitantly, the mRNA levels of glycolytic genes, such as hexokinase 1a (hk1a), hk1b, glucokinase and liver type of phosphofructokinase, were upregulated. The expression of glycogen synthase 1 and glycogen level in the AT increased between 3 and 8 HAF, suggesting that AT has the capacity to store excess glucose in tilapia. The decreased glycogen level together with upregulated transcription of glucose-6-phosphatase catalytic subunit a2 (g6pca2) at 24 HAF suggests that glycogen breakdown and glucose release from AT might contribute to circular glucose in tilapia. The opposite expression patterns between g6pca2 and phosphoenolpyruvate carboxykinase (pck) paralogs suggest that pck might participate in glyceroneogenesis rather than gluconeogenesis in the AT of tilapia. The mRNA levels of both cytosolic pck1 and mitochondrial pck2 increased during the period 1-8 HAF, and the expressions of lipogenic genes, such as acetyl-CoA carboxylase α and fatty acid synthase, were upregulated between 3 and 8 HAF, suggesting that glyceroneogenesis was probably stimulated as a source of glyceride-glycerol for triglyceride synthesis in the AT of tilapia. Taken together, our preliminary data suggest that AT plays an important role in the regulation of postprandial glucose homeostasis in the omnivorous tilapia, at least at the molecular level. [ABSTRACT FROM AUTHOR]

A common-garden experiment was carried out to compare two genetically distinct strains of Atlantic salmon (Salmo salar) fed diets with either high (CHO) or low (NoCHO) digestible carbohydrate (starch). Twenty salmon from either a commercial farmed strain (F) or a land-locked population (G) were placed in two tanks (10 fish of each population in each tank) and fed either CHO or NoCHO feeds. At the end of the experiment fish were fasted for 8 h, euthanized and blood and liver collected. Both diet and population had an effect on circulating glucose levels with G showing hypoglycaemia and dietary starch increasing this parameter. In contrast, G showed increased plasma triacylglycerol levels regardless of dietary treatment suggesting faster conversion of glucose to triacylglycerol. This different ability to metabolize dietary starch among strains was also reflected at a molecular (gene) level as most of the metabolic pathways evaluated were mainly affected by the factor population rather than by diet. The data are promising and suggest different regulatory capacities toward starch utilization between land-locked salmon and the farmed stock. Further analyses are necessary in order to fully characterize the capacity of land-locked salmon to utilize dietary carbohydrate. [ABSTRACT FROM AUTHOR]

Unlike the case of mammals, teleost fish generally have poor ability to utilize carbohydrate, and the clearance of glucose from the plasma is sluggish. In this study, after a 8‐week feeding trial, we conducted a glucose tolerance test to hypothesize that the capability of grass carp (Ctenopharyngodon idellus) to clear a glucose load is associated with its nutrient history of different carbohydrate‐to‐lipid ratio diets (CHO:L: 1.52%, 5.84% and 34.84%) through glycogen synthesis and glucose metabolic key enzymes. Our results showed that after a glucose load, the plasma glucose of fish fed with high CHO:L‐ratio diet (34.84%) first declined to baseline conditions, and the peak value of liver and muscle glycogen content was significantly higher in high CHO:L‐ratio but lower in low CHO:L group (1.52%). In addition, after glucose administration, hepatic GK (glucokinase) activity of fish fed with high CHO:L‐ratio diet increased more significantly than that of the other groups, and PEPCK (phosphoenolpyruvate carboxykinase) activity obviously decreased in low CHO:L‐ratio group. The results indicated that a long‐term adaptation to the high CHO:L‐ratio diet can improved the glucose tolerance of C. idellus through the promotion of glycogen synthesis and GK activity. [ABSTRACT FROM AUTHOR]

The present study was conducted to investigate the effects of insulin on serum glucose, hepatic glycogen content and expression of glucose metabolism-related genes in hybrid grouper. Triplicate groups of five fish were sampled at the 0, 1, 3, 6, 12, 24 or 48-h time point post-bovine insulin (5 μg 100/g fish body mass) injection. A significant decrease of serum glucose content was observed along with the depletion of hepatic glycogen content at the 12-h time point following insulin injection. Hepatic gene expression analysis revealed that the infusion of insulin significantly increased the expression of glucose transporters (GLUTs), GLUT1b and GLUT2. The transcription of gluconeogenesis-related genes, fructose-1,6-bisphosphatase 1a and glucose-6-phosphatase a catalytic subunit tandem duplicate 2, was significantly decreased at the 12-h time point, while the expression of glycolysis-related genes, phosphofructokinase liver b and pyruvate kinase L/R, was significantly up-regulated at the 24-h time point post-insulin injection. Meanwhile, the expression of glucokinase significantly increased immediately following insulin administration. The expression of glycogen synthase liver type significantly decreased at the 12-h time point, while the expression of glycogen phosphorylase liver type was significantly elevated at the 24-h time point following insulin injection. These results suggested that insulin could affect glucose metabolism through regulating gluconeogenesis, glycolysis and glycogen metabolism at the transcriptional level. [ABSTRACT FROM AUTHOR]

The RNA-binding protein quaking-a (Qkia) was cloned from the liver of blunt snout bream Megalobrama amblycephala through the rapid amplification of cDNA ends method, with its potential role in glucose metabolism investigated. The full-length cDNA of qkia covered 1,718 bp, with an open reading frame of 1,572 bp, which encodes 383 AA. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (97-99%) among most fish and other higher vertebrates. The mRNA of qkia was detected in all examined organs/tissues. Then, the plasma glucose levels and tissue qkia expressions were determined in fish intraperitoneally injected with glucose [1.67 g per kg body weight (BW)], insulin (0.052 mg/kg BW), and glucagon (0.075 mg/kg BW) respectively, as well as in fish fed two dietary carbohydrate levels (31 and 41%) for 12 weeks. Glucose administration induced a remarkable increase of plasma glucose with the highest value being recorded at 1 h. Thereafter, it reduced to the basal value. After glucose administration, qkia expressions significantly decreased with the lowest value being recorded at 1 h in liver and muscle and 8 h in brain, respectively. Then they gradually returned to the basal value. The insulin injection induced a significant decrease of plasma glucose with the lowest value being recorded at 1 h, whereas the opposite was true after glucagon load (the highest value was gained at 4 h). Subsequently, glucose levels gradually returned to the basal value. After insulin administration, the qkia expressions significantly decreased with the lowest value being attained at 2 h in brain and muscle and 1 h in liver, respectively. However, glucagon significantly stimulated the expressions of qkia in tissues with the highest value being gained at 6 h. Moreover, high dietary carbohydrate levels remarkably increased plasma glucose levels, but downregulated the transcriptions of qkia in tissues. These results indicated that the qkia gene of blunt snout bream shared a high similarity with that of the other vertebrates. Glucose and insulin administration, as well as high-carbohydrate feeding, remarkably down-regulated its transcriptions in brain, muscle and liver, whereas the opposite was true after the glucagon load. [ABSTRACT FROM AUTHOR]

Background: Glucose plays a key role as an energy source in most mammals, but its importance in fish appears to be limited that so far seemed to belong to diabetic humans only. Several laboratories worldwide have made important efforts in order to better understand this strange phenotype observed in fish. However, the mechanism of carbohydrate/glucose metabolism is astonishingly complex. Why basal glycaemia is different between fish and mammals and how carbohydrate metabolism is different amongst organisms is largely uncharted territory. The utilization of comparative systems biology with model vertebrates to explore fish metabolism has become an essential approach to unravelling hidden in vivo mechanisms. Results: In this study, we first built a database containing 791, 593, 523, 666 and 698 carbohydrate/glucose metabolic genes from the genomes of Danio rerio, Xenopus tropicalis, Gallus gallus, Mus musculus and Homo sapiens, respectively, and most of these genes in our database are predicted to encode specific enzymes that play roles in defined reactions; over 57% of these genes are related to human type 2 diabetes. Then, we systematically compared these genes and found that more than 70% of the carbohydrate/glucose metabolic genes are conserved in the five species. Interestingly, there are 4 zebrafish-specific genes (si:ch211-167b20.8, CABZ01043017.1, socs9 and eif4e1c) and 1 human-specific gene (CALML6) that may alter glucose utilization in their corresponding species. Interestingly, these 5 genes are all carbohydrate regulation factors, but the enzymes themselves are involved in insulin regulation pathways. Lastly, in order to facilitate the use of our data sets, we constructed a glucose metabolism database platform (http://101.200.43.1:10000/). Conclusions: This study provides the first systematic genomic insights into carbohydrate/glucose metabolism. After exhaustive analysis, we found that most metabolic genes are conserved in vertebrates. This work may resolve some of the complexities of carbohydrate/glucose metabolic heterogeneity amongst different vertebrates and may provide a reference for the treatment of diabetes and for applications in the aquaculture industry. [ABSTRACT FROM AUTHOR]

Environmental conditions experienced during early life play an important role in the long-term metabolic status of individuals. The present study investigated whether hypoxia exposure [for 24 h: 2.5 mg O2l-1 (20% dissolved O2)] during the embryonic stage alone (hypoxic history) or combined with a 5-day high-carbohydrate (60%) diet stimulus at first feeding (HC dietary history) can affect glucose metabolism later in life, i.e. in juvenile fish. After 19 weeks of growth, we observed a decrease in final body mass in fish with an HC dietary history. Feed efficiency was significantly affected by both hypoxic and HC dietary histories. After a short challenge test (5 days) performed with a 30% carbohydrate diet in juvenile trout, our results also showed that, in trout that experienced hypoxic history, mRNA levels of gluconeogenic genes in liver and glucose transport genes in both liver and muscle were significantly increased at the juvenile stage. Besides, mRNA levels of glycolytic genes were decreased in fish with an HC dietary history. Both hypoxic and dietary histories barely affected plasma metabolites or global epigenetic modifications in juvenile fish after the challenge test. In conclusion, our results demonstrated that an acute hypoxic stimulus during early development alone or combined with a hyperglucidic stimulus at first feeding can modify growth performance and glucose metabolism at the molecular level in juvenile trout. [ABSTRACT FROM AUTHOR]

In waterfowls, overfeeding leads to a hepatic steatosis, also called 'foie gras.' We decided to investigate the role of glucose metabolism in steatosis emergence. For this, we measured the expression of genes during the 12 h following the last meal of the overfeeding period. As expected, it showed that the expression of glucose transporter is more precocious in jejunal mucosa, especially for SGLT1, known to be the major transporter at the apical surface. In the liver, GLUT2 and HK1 are upregulated at the same time and seem to work together to import glucose. In peripherals tissues, such as muscle and subcutaneous adipose tissue (SAT), expression of genes of interest occurs later than the one in jejunum and liver. These results are in accordance with the evolution of glycemia. This study allows us to better understand the kinetic treatment of glucose after a meal in overfed ducks. It also will allow researchers to better target their sampling time knowing the optimal point of expression of each gene. [ABSTRACT FROM AUTHOR]

A 9-week feeding trial in floating freshwater cages (1.0 m×1.0 m×2.0 m) was conducted to study the effects of different dietary levels of protein and starch on growth, body composition, and gene expression of enzymes in common carp, Cyprinus carpio (mean body weight, 36.12±1.18 g) to evaluate the protein-sparing effect of dietary carbohydrate. Four diets were formulated with corn starch as the carbohydrate source to obtain corn starch levels of 6.5%, 13%, 19.5%, or 26% and protein levels of 30.5%, 28.2%, 26.4%, and 24.2%. The results showed no differences in growth performance of fish fed the diets with different protein and corn starch levels, but body composition and glucose metabolic enzyme activity of carp were significantly affected by the different diets ( P< 0.05). Weight gain, specific growth rate, and the feed conversion ratio were not different in fish fed the different dietary treatments. Protein efficiency ratio increased significantly as corn starch level increased ( P< 0.05). Whole-body crude lipid composition increased with increasing dietary corn starch level ( P< 0.05). Glucokinase (GK), hexokinase, and pyruvate kinase (PK) activities increased significantly with increasing dietary corn starch level ( P< 0.05), whereas glucose-6-phosphate (G6Pase) activity decreased with increasing dietary corn starch level ( P< 0.05). GK gene expression was significantly higher in fish fed the high-corn starch diet than those fed the low-corn starch diet ( P< 0.05). G6pase gene expression tended to decrease with increasing starch level ( P> 0.05). In summary, the results indicate a protein-sparing effect by substituting carbohydrate in the diet of common carp. [ABSTRACT FROM AUTHOR]

This study was designed to examine the cellular and systemic nutrient sensing mechanisms as well as the intermediary metabolism responses in turbot (Scophthalmus maximus L.) fed with fishmeal diet (FM diet), 45% of FM replaced by meat and bone meal diet (MBM diet) or MBM diet supplemented with essential amino acids to match the amino acid profile of FM diet (MBM+AA diet). During the one month feeding trial, feed intake was not affected by the different diets. However, MBM diet caused significant reduction of specific growth rate and nutrient retentions. Compared with the FM diet, MBM diet down-regulated target of rapamycin (TOR) and insulin-like growth factor (IGFs) signaling pathways, whereas up-regulated the amino acid response (AAR) signaling pathway. Moreover, MBM diet significantly decreased glucose and lipid anabolism, while increased muscle protein degradation and lipid catabolism in liver. MBM+AA diet had no effects on improvement of MBM diet deficiencies. Compared with fasted, re-feeding markedly activated the TOR signaling pathway, IGF signaling pathway and glucose, lipid metabolism, while significantly depressed the protein degradation signaling pathway. These results thus provided a comprehensive display of molecular responses and a better explanation of deficiencies generated after fishmeal replacement by other protein sources. [ABSTRACT FROM AUTHOR]

Four isolipidic and isoenergetic diets with different protein:carbohydrate (CH) contents (48:38, 52:34, 56:30, 60:26) were fed to juvenile Senegalese sole (22·01 (sem 0·01) g) during 104 d. Oral glucose tolerance tests were performed at the beginning (4 d) and at the end (104 d) of the experiment to assess the effect of the dietary treatment on glucose tolerance. Samples of blood, liver and muscle of all dietary groups were also obtained at the initial and final phases of the trial at different postprandial times (0, 1, 5 and 10 h after feeding) in order to analyse glucose and NEFA in plasma, and metabolites and enzyme activities involved in glycogen metabolism, glycolysis, gluconeogenesis and lipogenesis pathways in liver and muscle. The results obtained in this study suggest a good glucose tolerance in Senegalese sole. This species tolerated important amounts of CH in the diet without showing any deleterious signs in terms of growth or any metabolic disorders. After 104 d of feeding diets with an important amount of CH (48:38 and 52:34), the control of glycaemia was maintained and even postprandial glucose levels in plasma were (in general) lower than at the beginning of the experiment. This reasonable tolerance to glucose is also reflected by an increased use of glucose through glycolysis in liver (indicated by glucokinase activity), and the absence of changes in lipogenic potential in the same tissue (indicated by ATP citrate lyase activity). No clear changes were induced in the muscle by the dietary treatments. [ABSTRACT FROM PUBLISHER]

The rainbow trout (Oncorhynchus mykiss), a carnivorous fish species, displays a 'glucose-intolerant' phenotype when fed a highcarbohydrate diet. The importance of carbohydrate metabolism during embryogenesis and the timing of establishing this later phenotype are currently unclear. In addition, the mechanisms underlying the poor ability of carnivorous fish to use dietary carbohydrates as a major energy substrate are not well understood. It has recently been shown in trout that duplicated genes involved in glucose metabolism may participate in establishing the glucoseintolerant phenotype. The aim of this study was therefore to provide new understanding of glucose metabolism during ontogenesis and nutritional transition, taking into consideration the complexity of the trout genome. Trout were sampled at several stages of development from fertilization to hatching, and alevins were then fed a noncarbohydrate or a high-carbohydrate diet during first feeding. mRNA levels of all glucose metabolism-related genes increased in embryos during the setting up of the primitive liver. After the first meal, genes rapidly displayed expression patterns equivalent to those observed in the livers of juveniles. g6pcb2.a (a glucose 6-phosphatase-encoding gene) was up-regulated in alevins fed a high-carbohydrate diet, mimicking the expression pattern of gck genes. The g6pcb2.a gene may contribute to the non-inhibition of the last step of gluconeogenesis and thus to establishing the glucose-intolerant phenotype in trout fed a high-carbohydrate diet as early as first feeding. This information is crucial for nutritional programming investigations as it suggests that first feeding would be too late to programme glucose metabolism in the long term. [ABSTRACT FROM AUTHOR]

The article discusses hormonal and metabolite regulation of hepatic glucokinase. It states role of glucokinase activity in glucose metabolism, and mentions that glucokinase activity is dependent on binding of glucokinase to a specific inhibitor protein, glucokinase regulatory protein. It notes that Glucokinase is inhibited in postabsorptive state by sequestration in the nucleus bound to GKRP, and cites that altered binding affinity for glucokinase is associated with increase lipid levels.

To assess the effect of feeding frequency on the utilization of dietary starch by white sea bream juveniles, triplicate groups of fish were fed an experimental diet (400 g kg−1 protein, 140 g kg−1 lipids and 350 g kg−1 pregelatinized maize starch) to apparent visual satiation 2, 3 or 4 times a day for 63 days. Growth performance, feed utilization efficiency, glycaemia, cholesterolaemia, plasma triacylglycerides, liver lipids and glycogen content were unaffected by feeding frequency. α-Amylase activity increased from the pyloric caeca to the posterior intestine and was higher in fish fed twice a day than in fish fed 3 or 4 times a day. Hepatic glucokinase ( GK) activity decreased with the increase in feeding frequencies, whereas fructose-1,6-bisphosphatase ( FBPase) activity increased. Hepatic glucose-6-phosphate dehydrogenase and glutamate dehydrogenase activities were unaffected by feeding frequency. Overall, feeding frequency did not improve white sea bream dietary starch utilization. α-Amylase, GK and FBPase activities responded to dietary starch consumed at each meal, denoting a good metabolic adaptation of the fish to the feeding conditions. [ABSTRACT FROM AUTHOR]

Rainbow trout are generally considered to be poor glucoregulators. To evaluate this, exogenous glucose was administered to chronically hyperglycemic fish at twice the endogenous rate of hepatic production, and their ability to modulate glucose fluxes was tested. Our goals were to determine: (1) whether hyperglycemic fish maintain higher glucose fluxes than normal; (2) whether they can lower hepatic production (Ra glucose) or stimulate disposal (Rd glucose) to cope with a carbohydrate overload; and (3) an estimate of the relative importance of glucose as an oxidative fuel. Results show that hyperglycemic trout sustain elevated baseline Ra and Rd glucose of 10.6±0.1 µmol kg–1 min–1 (or 30% above normal). If 50% of Rd glucosewas oxidized as in mammals, glucose could account for 36 to 100% of metabolic rate when exogenous glucose is supplied. In response to exogenous glucose, rainbow trout can completely suppress hepatic glucose production and increase disposal 2.6-fold, even with chronically elevated baseline fluxes. Such large changes in fluxes limit the increase in blood glucose to 2.5-fold and are probably mediated by the effects of insulin on glucose transporters 2 and 4 and on key enzymes of carbohydrate metabolism. Without this strong and rapid modulation of glucose kinetics, glycemia would rise four times faster to reach dangerous levels, exceeding 100 mmol l–1. Such responses are typical of mammals, but rather unexpected for an ectotherm. The impressive plasticity of glucose kinetics demonstrated here suggests that trout have a much better glucoregulatory capacity than is usually portrayed in the literature. [ABSTRACT FROM AUTHOR]

In the present study, the effects of partial substitution of dietary protein by digestible starch on endogenous glucose production were evaluated in European seabass (Dicentrarchus labrax). The fractional contribution of dietary carbohydrates v. gluconeogenesis to blood glucose appearance and hepatic glycogen synthesis was quantified in two groups of seabass fed with a diet containing 30 % digestible starch (DS) or without a carbohydrate supplement as the control (CTRL). Measurements were performed by transferring the fish to a tank containing water enriched with 5 % 2H2O over the last six feeding days, and quantifying the incorporation of 2H into blood glucose and hepatic glycogen by 2H NMR. For CTRL fish, gluconeogenesis accounted for the majority of circulating glucose while for the DS fish, this contribution was significantly lower (CTRL 85 (sem 4) % v. DS 54 (sem 2) %; P< 0·001). Hepatic glycogen synthesis via gluconeogenesis (indirect pathway) was also significantly reduced in the DS fish, in both relative (CTRL 100 (sem 1) % v. DS 72 (sem 1) %; P< 0·001) and absolute terms (CTRL 28 (sem 1) v. DS 17 (sem 1) μmol/kg per h; P< 0·001). A major fraction of the dietary carbohydrates that contributed to blood glucose appearance (33 (sem 1) % of the total 47 (sem 2) %) had undergone exchange with hepatic glucose 6-phosphate. This indicated the simultaneous activity of hepatic glucokinase and glucose 6-phosphatase. In conclusion, supplementation of digestible starch resulted in a significant reduction of gluconeogenic contributions to systemic glucose appearance and hepatic glycogen synthesis. [ABSTRACT FROM PUBLISHER]

Arginine has been demonstrated to enhance glucose and lipid oxidation in mammals through activation of polyamine turnover. We aimed to investigate how arginine affects energy utilization through polyamine metabolism and whether this effect is time dependent. Primary liver cells were isolated from Atlantic salmon (2.2 kg body weight) fed diets containing 25.5 (low arginine, LA) or 36.1 (high arginine, HA) g arginine/kg dry matter for 12 weeks, to investigate the effect of long-term arginine supplementation. The cells were cultured for 24 h in L-15 medium to which either alpha-difluoromethylornithine (DFMO) or N, N-diethylnorspermine (DENSPM) was added. Analysis of the medium by nuclear magnetic resonance revealed significant differences between the two dietary groups as well as between cells exposed to DFMO and DENSPM, with decreased glucose, fumarate and lactate concentrations in media of the HA cells. Liver cells from fish fed the HA diet had higher spermidine/spermine- N1-acetyltransferase protein abundance and lower adenosine triphosphate concentration as compared to the LA-fed fish, while gene expression was not affected by either diet or treatment. Primary liver cells isolated from salmon fed a commercial diet and cultured in L-15 media with or without arginine supplementation (1.82 or 3.63 mM) for 48 h, representing short-term effect of arginine supplementation, showed differential expression of genes for apoptosis and polyamine synthesis due to arginine supplementation or inhibition by DFMO. Overall, arginine concentration and exposure time affected energy metabolism and gene regulation more than inhibition or activation of key enzymes of polyamine metabolism, suggesting a polyamine-independent influence of arginine on cellular energy metabolism and survival. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the role of soluble non-starch polysaccharide (guar gum) on white sea bream Diplodus sargus, glucose and lipid metabolism. A control diet was formulated to contain 40 % crude protein, 14 % crude lipids and 35 % pregelatinized maize starch, and three other diets were formulated similar to the control diet except for guar gum, which was included at 4 % (diet GG4), 8 % (diet GG8) or 12 % (diet GG12). Diets were fed to the fish for 9 weeks on a pair-feeding scheme. Guar gum had no effect on growth performance, feed efficiency, glycaemia, cholesterolaemia and plasma triacylglyceride levels. Hepatic glucokinase and pyruvate kinase activities, liver glycogen content and liver insulin-like growth factor-I gene expression were not affected by dietary guar gum, while fructose-1,6-bisphosphatase activity was lower in fish fed guar gum-supplemented diets. Hepatic glucose-6-phosphate dehydrogenase activity was higher in fish fed diets GG4 and GG8 than in the control group. Overall, data suggest that in contrast to mammals guar gum had no effect on white sea bream glucose utilization and in lowering plasma cholesterol and triacylglyceride levels. However, it seems to contribute to lower endogenous glucose production. [ABSTRACT FROM AUTHOR]

Mammalian studies report that methionine restriction (MR) as a dietary regimen extends life span, delays the onset of age-related diseases and enhances fat oxidation in obese subjects with metabolic syndromes. However, the underlying cellular signalling pathways are poorly understood. Rainbow trout (Oncorhynchus mykiss) is a glucose-intolerant species, providing an excellent model for the study of carbohydrate metabolism. MR diets in combination with 12 % (+/ − ) and 22 % (+/ − ) carbohydrate-rich meals were fed to rainbow trout for a period of 8 weeks and phenotypic and transcript expression changes in the liver and white muscle were assessed. Fish fed MR diets, irrespective of carbohydrate load, were shown to abolish the glucose-intolerant phenotype 6 h post-feeding. There was a distinct switch in glucose and glycogen content in the liver of fish fed MR diets, with a significantly higher concentration of glycogen, suggesting reduced glycolytic capacity. Transcriptional responses to MR demonstrated decreased expression of hepatic fatty acid synthase, sterol regulatory binding protein 1, PPARγ coactivator 1-α and PPARα, indicative of a reduction in the de novo synthesis of fatty acids and cholesterol, and a potential decrease in hepatic fat oxidative capacity. Muscle adenylate charge was depressed under MR, and increased expression of AMP-activated protein kinase α1 was detected, indicative of reduced energy availability. Total DNA methylation showed that carbohydrate load, rather than MR, dictated hypomethylation of genomic DNA. This is the first study which demonstrates that MR can abolish a glucose-intolerant phenotype in trout, and identifies trout as a suitable model for studying metabolic syndromes. [ABSTRACT FROM PUBLISHER]

Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes. [ABSTRACT FROM AUTHOR]

Glucose and lipid metabolism in pancreatic islet organs is poorly characterized. In the present study, using as a model the carnivorous rainbow trout, a glucose-intolerant fish, we assessed mRNA expression levels of several genes involved in glucose and lipid metabolism (including ATP-citrate lyase; carnitine palmitoyltransferase-1 isoforms, CPT; the mitochondrial isoform of the phospho enolpyrutave carboxykinase, mPEPCK and pyruvate kinase, PK) and glucosensing (glucose transporter type 2, Glut2; glucokinase, GK and the potassium channel, K) in Brockmann bodies. We evaluated the response of these parameters to changes in feeding status (food deprived vs. fed fish) as well as to changes in the amount of carbohydrate (dextrin) in the diet. A general inhibition of the glycolytic (including the glucosensing marker GK) and β-oxidation pathways was found when comparing fed versus food-deprived fish. When comparing fish feeding on either low- or high-carbohydrate diets, we found that some genes related to lipid metabolism were more controlled by the feeding status than by the carbohydrate content (fatty acid synthase, CPTs). Findings are discussed in the context of pancreatic regulation of glucose and lipid metabolism in fish, and show that while trout pancreatic metabolism can partially adapt to a high-carbohydrate diet, some of the molecular actors studied seem to be poorly regulated (K) and may contribute to the glucose intolerance observed in this species when fed high-carbohydrate diets. [ABSTRACT FROM AUTHOR]

AMPK, a master metabolic switch, mediates the observed increase of glucose uptake in locomotory muscle of mammals during exercise. AMPK is activated by changes in the intracellular AMP:ATP ratio when ATP consumption is stimulated by contractile activity but also by AICAR and metformin, compounds that increase glucose transport in mammalian muscle cells. However, the possible role of AMPK in the regulation of glucose metabolism in skeletal muscle has not been investigated in other vertebrates, including fish. In this study, we investigated the effects of AMPK activators on glucose uptake, AMPK activity, cell surface levels of trout GLUT4 and expression of GLUT1 and GLUT4 as well as the expression of enzymes regulating glucose disposal and PGC1α in trout myotubes derived from a primary muscle cell culture. We show that AICAR and metformin significantly stimulated glucose uptake (1.6 and 1.3 fold, respectively) and that Compound C completely abrogated the stimulatory effects of the AMPK activators on glucose uptake. The combination of insulin and AMPK activators did not result in additive nor synergistic effects on glucose uptake. Moreover, exposure of trout myotubes to AICAR and metformin resulted in an increase in AMPK activity (3.8 and 3 fold, respectively). We also provide evidence suggesting that stimulation of glucose uptake by AMPK activators in trout myotubes may take place, at least in part, by increasing the cell surface and mRNA levels of trout GLUT4. Finally, AICAR increased the mRNA levels of genes involved in glucose disposal (hexokinase, 6-phosphofructokinase, pyruvate kinase and citrate synthase) and mitochondrial biogenesis (PGC-1α) and did not affect glycogen content or glycogen synthase mRNA levels in trout myotubes. Therefore, we provide evidence, for the first time in non-mammalian vertebrates, suggesting a potentially important role of AMPK in stimulating glucose uptake and utilization in the skeletal muscle of fish. [ABSTRACT FROM AUTHOR]

The main objective of the present study was to evaluate the relative contribution of the intestine to glucose homeostasis in rainbow trout. In a first set of in vivo experiments trout were subjected to oral glucose treatments alone or in combination with insulin injections to assess changes in glucose-related enzymes activities, metabolite levels, and mRNA levels. Rainbow trout gut displays an important glucose metabolism that includes the ability to store glucose as glycogen (mostly in the muscle layers) and a large capacity to oxidize glucose. This constitutes a surprising result for a carnivorous fish. In a second set of in vivo experiments, trout received an oral amino acid solution alone or in combination with insulin injection to determine whether other factors besides fasting could regulate gluconeogenesis in intestine. The results confirm the absence of regulation of gluconeogenesis in trout gut, which does not respond to hormones, glucose, lactate, or amino acid changes, either in vivo or in vitro. We also fully characterized gut glucose metabolism in vitro. We observed that a large amount of glucose is oxidized to lactate, supporting the importance of glucose in gut metabolism. Moreover, we corroborated the minor actions of insulin in trout gut, whereas other hormones such as glucagon-like peptide-1 and C-peptide appear to be major hormonal regulators of glucose metabolism in fish gut. Finally, we obtained the first evidence for the existence of a glucosensing mechanism in the midgut of this carnivorous species. [ABSTRACT FROM AUTHOR]

Rainbow trout are considered as a poor user of dietary carbohydrates, displaying persistent postprandial hyperglycaemia when fed a diet containing high amounts of carbohydrates. While this phenotype is well-described in juveniles, less attention was given to broodstock. Our objective was to assess for the first time the short-term consequences of feeding mature female and male, and neomale trout with a low-protein high-carbohydrate diet on glucose and lipid metabolism. Fish were fed for two days with a diet containing either no or 32% of carbohydrates. We analysed plasma metabolites, mRNA levels and enzymatic activities of glycolysis, gluconeogenesis, de novo lipogenesis and β-oxidation in the liver. Results demonstrated that the glucose and lipid metabolism were regulated by the nutritional status in all sexes, irrespective of the carbohydrate intake. These data point out that carbohydrate intake during a short period (5 meals) at 8 °C did not induce specific metabolic changes in broodstock. Finally, we demonstrated, for the first time, sex differences regarding the consequences of two days of feeding on glucose and lipid metabolism. [ABSTRACT FROM AUTHOR]

Although feed cost is the greatest concern in aquaculture, the inclusion of carbohydrates in the fish diet, and their assimilation, are still not well understood in aquaculture species. We identified molecular events that occur due to the inclusion of high carbohydrate levels in the diets of genetically improved 'Jayanti rohu' Labeo rohita. To reveal transcriptional changes in the liver of rohu, a feeding experiment was conducted with three doses of gelatinized starch (20% (control), 40%, and 60%). Transcriptome sequencing revealed totals of 15,232 (4464 up- and 4343 down-regulated) and 15,360 (4478 up- and 4171 down-regulated) differentially expressed genes. Up-regulated transcripts associated with glucose metabolisms, such as hexokinase, PHK, glycogen synthase and PGK, were found in fish fed diets with high starch levels. Interestingly, a de novo lipogenesis mechanism was found to be enriched in the livers of treated fish due to up-regulated transcripts such as FAS, ACCα, and PPARγ. The insulin signaling pathways with enriched PPAR and mTOR were identified by Kyoto Encyclopedia of Genes and Genome (KEGG) as a result of high carbohydrates. This work revealed for the first time the atypical regulation transcripts associated with glucose metabolism and lipogenesis in the livers of Jayanti rohu due to the inclusion of high carbohydrate levels in the diet. This study also encourages the exploration of early nutritional programming for enhancing glucose efficiency in carp species, for sustainable and cost-effective aquaculture production. [ABSTRACT FROM AUTHOR]

The article focuses on the research "High or low dietary carbohydrate: protein ratios during first-feeding affect glucose metabolism and intestinal microbiota in juvenile rainbow trout" conducted by I. Geurden and others, published in the previous issue of the journal. Topics discussed include benefits of aquaculture revolution in catering sea food needs of the society, experiments to develop carbohydrate-rich fish diets, and effect of high carbohydrate diet on gut flora and metabolism of fish.