Carbohydrate Metabolism In Fish Research Articles

New insights on intestinal microorganisms and carbohydrate metabolism in fish

New insights on intestinal microorganisms and carbohydrate metabolism in fish

Insights into the correlations between prebiotics and carbohydrate metabolism in fish: Administration of xylooligosaccharides in Megalobrama amblycephala offered a carbohydrate-enriched diet

Dietary supplementation of xylooligosaccharides (XOS) represents a potential means to improve the carbohydrate metabolic disorders in type 2 diabetes. However, whether XOS could improve the carbohydrates utilization and metabolism of fish is still unknown. This study investigated the effects of XOS on the growth performances and glycolipid metabolism of blunt snout bream (Megalobrama amblycephala) fed a high carbohydrate (HC) diet. Fish (44.69 ± 0.11 g) were fed a control diet (29% carbohydrate), a HC diet (41% carbohydrate), and the HC diet supplemented with 0.5%, 1.0%, 1.5% and 2.0% XOS respectively for 12 weeks. Compared with the control group, the HC group obtained significantly high values of final body weight, weight gain rate, intraperitoneal fat ratio, whole-body lipid content, liver and intraperitoneal fat glycogen contents, tissue lipid contents, glycated serum protein (GSP) levels, and the transcriptions of sodium glucose cotransporter 1, glucose transporter 2 (glut2), glucokinase (gk), pyruvate kinase (pk), glycogen synthase (gs), fatty acid synthetase (fas) and acetyl-CoA carboxylase α (accα), and the decreased values of feed conversion ratio and hepatic transcriptions of carnitine palmitoyl transferase 1 (cpt-1) and acyl-CoA oxidase (aco). Meanwhile, the supplementation of 1.0% XOS significantly increased the nitrogen retention efficiency, liver glycogen contents, and the transcriptions of glut2, gk, pk, glucose-6-phosphate, cpt-1 and aco compared with the HC group, while the opposite was true for liver and muscle lipid contents, plasma TG, total cholesterol and GSP levels, and the transcriptions of fas and accα. Collectively, dietary supplementation of 1.0% XOS could improve the growth performance and glycolipid metabolism of blunt snout bream fed a high-carbohydrate diet by up-regulating glucose transport, glycolysis, glycogenesis, the pentose phosphate pathway and fatty acids β-oxidation, but down-regulating gluconeogenesis and fatty acid biosynthesis

Forkhead transcription factor O1 (FoxO1) in torafugu pufferfish Takifugu rubripes: Molecular cloning, in vitro DNA binding, and target gene screening in fish metagenome.

The fish insulin/insulin-like growth factor (IGF) pathway has weak control over carbohydrate metabolism. To understand the molecular basis for the metabolic diversity, we characterized the forkhead box transcription factor O1A (FoxO1A), a downstream target of the insulin/IGF pathway, in torafugu Takifugu rubripes. The cloned torafugu FoxO1A cDNA contained all conserved features critical for its transcriptional activity and a unique unspliced intron encoding a poly-glutamine stretch. Torafugu FoxO1A showed the IGF-dependent nuclear exclusion and in vitro binding to the well-conserved FoxO1 binding site, DAF-16 binding element (DBE), but failed to bind to the insulin-responsive element by which mammalian FoxO1 mediates insulin effects. The subsequent in silico genomic screening provided a list of 587 potential torafugu FoxO1A target genes containing the DBE. Some carbohydrate metabolic genes regulated by FoxO1 in mammals were not included in the list. We further identified about 250 potential fish FoxO1 target genes by integrating results of the DBE screening against fish metagenome that contained 262 species. Neuronal processes appeared to be the common major function of fish FoxO1, although further annotation of the potential target genes is required. These results provide a part of the molecular basis underlying the weak association between the insulin/IGF pathway and carbohydrate metabolism in fish.

Molecular cloning, characterization and expression analysis of glucose transporters fromRachycentron canadum

It is very necessary to clarify the mechanism of carbohydrate metabolism in fish due to their poor ability to utilize carbohydrates. Glucose transporters (GLUTs) are important carriers involved in glucose transport across the plasma membrane, which is the first rate-limiting step of carbohydrate metabolism. In this study, five glucose transporters (RcGLUT1, RcGLUT2, RcGLUT3, RcGLUT5 and RcGLUT9) were obtained from Rachycentron canadum. The complete cDNAs open reading frames (ORF) of RcGLUT1, RcGLUT2, RcGLUT3, RcGLUT5 and RcGLUT9 were 1,476 bp, 1,530 bp, 1,551 bp, 1,539 bp and 1,578 bp (GenBank accession no. MK560257, MK560258, MH184460, MH184461 and MH184462), encoding 491, 509, 516, 512 and 525 amino acid (aa) residues respectively. All five RcGLUTs contained a Sugar_tr domain, which is an important feature of the GLUT gene family. The multiple sequence alignment and phylogenetic relationship analyses showed that RcGLUTs were highly conserved and homologous from fish to mammals. Examination of tissue distribution showed that RcGLUTs were expressed constitutively in R. canadum. RcGLUT1-5 and RcGLUT9 had the highest expression in the foregut, kidneys, haemocytes, muscles, liver and heart respectively. All six RcGLUTs first increased to peak levels of expression and then reduced both in the liver and muscle after fasting. The exception is that the expression levels of RcGLUT4 and RcGLUT5 in muscle were significantly lower than the control. In response to hypoxia, only RcGLUT2 in the liver and muscle and RcGLUT9 in muscle were expressed at a significantly lower level relative to the control. In sum, all RcGLUTs in the liver and muscles showed significant changes in response to fasting and hypoxia, suggesting that GLUT genes may play a role in the response to common physiological stresses.

Transcriptome, enzyme activity and histopathology analysis reveal the effects of dietary carbohydrate on glycometabolism in juvenile largemouth bass, Micropterus salmoides

Largemouth bass (Micropterus salmoides) is one of the most valuable freshwater aquatic species in China. However, M. salmoides appeared to use dietary carbohydrate more poorly than other carnivorous fish. Although carbohydrate metabolism of fish has been well studied for the past decades, studies regarding transcriptomic profiling of carbohydrate metabolism in fish are lacking. In this study, the transcriptomic profiles of M. salmoides liver were explored for the first time by feeding seven kinds of diets, and selectively analyzed the glycometabolism at different levels of dietary carbohydrate (ML-120 g kg−1, MM-240 g kg−1, and MH-360 g kg−1). Totally, the de novo assemblies yielded 50,743 unigenes with an average of 1169 bp. The assembled unigenes were evaluated and functionally annotated by comparing with sequences in major public databases including protein sequence (Nr), Clusters of Orthologous Groups (COG), Swiss-Prot, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology database (GO). Comparison of gene expression levels revealed that differentially expressed genes (DEGs) (P < .05): a total of 9096 (613 up-regulated and 8483 down-regulated genes) was obtained between ML and MM; 5778 (414 up-regulated and 5365 down-regulated) was obtained between MH and MM. Moreover, 12 carbohydrate metabolism-related genes were selected for quantitative real-time PCR analysis to validate the RNA-Seq data. The results confirmed the consistency of the expression levels between RNA-Seq and qRT-PCR data. Meanwhile, present study also examined the related enzyme activities of carbohydrate metabolism. The results showed that high level of dietary carbohydrate (360 g kg−1) exhibited a strong inhibitory effect on the genes of M. salmoides. Dietary carbohydrate in MM up-regulated 93.3% of differential expression genes (DEGs) compared to ML, however, 92.9% of the DEGs in MH were depressed compared to MM. This trend is also reflected in the corresponding enzyme activities in general. With dietary carbohydrate increase, there were severe histological alterations in M. salmoides liver. Collectively, this study shows a systematic overview of the transcriptome analysis in M. salmoides, and provides valuable gene information for studying molecular mechanisms of carbohydrate metabolism in freshwater fish.

Long-term administration of benfotiamine benefits the glucose homeostasis of juvenile blunt snout bream Megalobrama amblycephala fed a high-carbohydrate diet

This study aimed to investigate the effects of benfotiamine on growth performance, glucose homeostasis and intermediary glucose metabolism of blunt snout bream (Megalobrama amblycephala). A total of 240 fish (average body weight: 24.24±0.05g) were randomly distributed into 12 tanks and fed three diets (control, diet with 30% carbohydrate; HC, diet with 43% carbohydrate; HCB, HC diet supplemented with 2.85mg/kg benfotiamine) for 12weeks. The results indicated that fish fed the HCB diet had a lower specific growth rate and feed conversion ratio compared to those fed the control and HC diets, whereas protein efficiency ratio, nitrogen retention efficiency and energy retention efficiency showed an opposite trend. Additionally, fish offered HCB diet showed relatively high values of whole-body lipid contents, tissue glycogen and lipid contents and plasma insulin levels, whereas plasma levels of glucose, advanced glycation end products and glycated serum protein significantly decreased compared with other treatments. Furthermore, benfotiamine improved the glucose tolerance of fish fed HC diet after a glucose load. High carbohydrate intake significantly up-regulated the mRNA levels of glucokinase, pyruvate kinase, glucose transporter 2, glycogen synthase, fatty acid synthetase and glucose-6-phosphate dehydrogenase, whereas the opposite was true for phosphoenolpyruvate carboxykinase, fructose-1,6-biphosphatase, glucose-6-phosphatase, carnitine palmitoyl transferase I and acyl-CoA oxidase. This also held true for fish fed HCB diet except for fatty acid oxidation process which was further enhanced. Overall, these findings suggested that benfotiamine benefited the glucose metabolism of Megalobrama amblycephala fed high-carbohydrate diet through the stimulation of glycolysis, glycogenesis, lipogenesis and fatty acid oxidation coupled with the depression of gluconeogenesis.Statement of relevanceThis study investigated the effects of dietary benfotiamine supplementation on growth performance, glucose homeostasis and intermediary metabolism of blunt snout bream. The data obtained here will facilitate our understanding of the potential mechanisms concerning the beneficial effects of benfotiamine on the carbohydrate metabolism of fish. It is also helpful for the development of low-protein and high-energy feed for fish.

Molecular characterization and expression analysis of glucokinase from herbivorous fish Megalobrama amblycephala subjected to a glucose load after the adaption to dietary carbohydrate levels

A full-length cDNA coding glucokinase (GK) was cloned from Megalobrama amblycephala by RT-PCR and RACE approaches. The cDNA obtained covered 2090bp with an open reading frame of 1431bp encoding 476 amino acids. Sequence alignment and phylogenetic analysis revealed a high degree of conservation (84–99%) among most fish and higher vertebrates, retaining one hexokinase signature sequence, one ATP-binding domain, two N-linked glycosylation sites and several glucose-binding sites. The highest GK expression was observed in the liver followed by intestine, whereas relatively low values were detected in the muscle, kidney and brain. Then, plasma glucose levels and liver GK activities and expressions were determined in fish subjected to a glucose load after being fed two dietary carbohydrate levels (30% and 42%) for 11weeks. Plasma glucose levels decreased significantly after high-carbohydrate adaption. Glucose load induced a remarkable increment of glycemia in both groups with the maximum level being attained at 1h. Thereafter, it decreased significantly to the basal value at 6h and kept constant afterward. Hepatic GK expressions in both groups increased significantly with the maximum value being attained at 2h after the glucose load, whereas no statistical difference was observed in enzymatic activities during the first 4h. Then, both the activities and expressions decreased significantly with further increasing time. In addition, an inducible liver GK activity and expression by dietary carbohydrate levels were both observed. The results indicated that the GK gene of Megalobrama amblycephala showed a typical structure of the hexokinase family, and shared a high similarity with that of the other vertebrates. Hepatic GK expressions and activities of this species were highly inducible by glucose administration, as favored a short postprandial period of hyperglycemia. Furthermore, high dietary carbohydrate improved its glucose tolerance through the enhanced GK expressions and activities.Statement of relevance:This study investigated the mRNA expressions and activities of GK in herbivorous Megalobrama amblycephala subjected to a glucose load after the adaption to dietary carbohydrate levels. The data obtained here will facilitate the understanding of the molecular events involved in the carbohydrate metabolism of fish. It is also helpful for the development of low-protein and high-energy feed for fish.

Glucose metabolism in fish: a review

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.

Expression of Human Glucose Transporter Type 1 and Rat Hexokinase Type II Complementary DNAs in Rainbow Trout Embryos: Effects on Glucose Metabolism.

: Sugars are utilized poorly in fish mainly because of low rates of transport across plasma membrane and phosphorylation. To evaluate whether it is possible to augment carbohydrate metabolism in fish using heterologous genes, expression of human glucose transporter type 1 (hGLUT1) and rat hexokinase type II (rHKII) complementary DNAs cloned with cytomegalovirus promoter was followed in rainbow trout embryos. Both genes were transcribed. Hexokinase activity, undetectable in control, was found in transformed blastulas. Increased rates of 14C-methylglucose uptake and sensitivity to cytochalasin B indicated the presence of facilitative hexose transport due to hGLUT1 expression. Effect of hGLUT1 on production of 14CO2 from glucose was greater than that of rHKII. Coexpression of the genes did not increase the rate of glucose oxidation compared with expression of hGLUT1 alone.

Lindane-induced changes in carbohydrate metabolism in Anguilla anguilla

1. Anguilla anguilla (L.) was exposed to a sublethal concentration of 0.167 ppm (0.25 of the 96-hr lc 50) of lindane for 6, 12, 24, 48, 72 and 96 hr. 2. Changes in glycogen, glucose, pyruvate and lactate contents of liver and muscle after lindane exposure, were studied. 3. Muscle and liver glycogen levels decreased significantly during the exposure time. Muscle glucose values increased but on the other hand we found a decrease in those of liver. 4. Muscle and liver pyruvate content increased as did lactate levels in both tissues. 5. The observed effects of lindane on carbohydrate metabolism in fish are discussed in relation to acute stress syndrome.

Effects of lindane on fish carbohydrate metabolism

Exposure of the European eel ( Anguilla anguilla) to a high sublethal concentration of 0.335 ppm (0.50 of the 96-hr LC 50) of lindane for 6, 12, 24, 48, 72, and 96 hr affected carbohydrate metabolism. Muscle glycogen levels decreased significantly ( P < 0.05) at 6, 12, 24, 48, 72, and 96 hr; liver glycogen content did not decline at any time. Muscle glucose levels in fish were elevated at 6, 12, 24, 48, 72, and 96 hr but in liver, the levels increased only at 96 hr. Mean values of muscle and liver pyruvate were elevated significantly ( P < 0.05) at 6, 12, 24, 48, and 72 hr. Muscle lactate levels increased at 6, 12, 24, and 48 hr in pesticide-treated fish. Liver lactate levels were elevated only at 12, 24, and 48 hr of treatment. The observed effects of lindane on carbohydrate metabolism in fish are discussed in relation to acute stress syndrome. Measurement of carbohydrate metabolites in fish for 6 hr or longer could prove useful as a rapid method for evaluating the toxicity of pesticides and other toxicants.

Subchronic metabolic effects and toxicity of a simulated pulp mill effluent on juvenile lake trout, Salmo trutta m. lacustris

Juvenile lake trout ( Salmo trutta m. lacustris) were exposed for 7 weeks to 0.05× and 0.2 × 96-hr LC 50 concentrations of simulated bleached kraft pulp mill effluent (KME − Sa + CP). A sulfate soap preparation, composed mainly of resin and fatty acids, with added chlorophenols (CP, tri-, tetra-, and penta-CP) was used as the toxicant mixture. Concentrations of free CP in plasma and free and conjugated CP in bile were proportional to their concentrations in the water. The greatest total gradient between bile and water CP was 5.2 × 10 4 for pentachlorophenol. The activity of a liver polysubstrate monooxygenase (PSMO) system, assayed with three model substrates, increased 40 to 67% due to KME − Sa + CP. However, the increase was not directly dependent on the exposure concentration. In contrast to PSMO, activities of conjugating enzymes ( p-nitrophenol UDP-glucuronosyl and glutathione transferases) were decreased in the liver. Increased concentration of glutathione was noted in the liver and kidney. In addition, a small (9%) but significant decrease in blood hemoglobin concentration was observed at the higher exposure concentration. Although growth rate of lake trout was markedly decreased due to KME − Sa + CP, hydromineral balance and carbohydrate metabolism in fish were unaffected, indicating possible physiological compensation. On the other hand, lethality tests with lake trout preexposed to KME − Sa + CP at 0.2 × LC 50 revealed decreased tolerance, whereas at the lower exposure concentration it was unchanged. We therefore conclude that various physiological adjustments in trout during subchronic exposures were not adaptive in terms of short-term tolerance.

Effects of endosulfan on fish carbohydrate metabolism

Exposure of the Indian catfish ( Heteropneustes fossilis) to a high sublethal concentration of 0.0015 ppm (0.75 of the 96-hr LC 50) of endosulfan for 3, 6, 12, 48, and 96 hr affected carbohydrate metabolism. Muscle glycogen levels decreased significantly at 3, 6, 48, and 96 hr; liver glycogen content declined at 6 hr but there was a resynthesis of liver glycogen stores at 12 hr. Blood glucose levels in fish were elevated at 3, 6, 48, and 96 hr. Mean values of blood pyruvate were elevated significantly at 6 and 48 hr. Blood lactate levels were elevated at 3 and 6 hr but hypolacticemia resulted at 12 and 96 hr in pesticide-treated fish. The observed effects of endosulfan on carbohydrate metabolism in fish are discussed in relation to acute stress syndrome. Measurement of carbohydrate metabolites in fish for 3 hr or longer could prove useful as a rapid method for evaluating toxicity of pesticides and other toxicants.

Effect of a paired mixture of aldrin and formothion on carbohydrate metabolism in a fish, Heteropneustes fossilis

Exposure of the Indian catfish ( Heteropneustes fossilis) to a high sublethal concentration, 0.114 ppm (0.8 of the 96-hr LC 50) of a mixture of aldrin and formothion, added in a one-to-one ratio, for 3, 6, 12, 48, and 96 hr affected carbohydrate metabolism. Muscle glycogen decreased significantly at 6 and 48 hr; hepatic glycogen content declined at 3, 6, 12, and 48 hr in exposed fish. Blood glucose levels in fish were significantly decreased at 3, 12, 48, and 96 hr. Mean value of blood pyruvate was significantly depressed at 3 hr. Blood lactate levels were elevated at 3, 6, 12, and 96 hr in pesticide-treated fish. The observed effects of the mixture of aldrin and formothion on carbohydrate metabolism in fish could prove useful as a rapid method for evaluating toxicity of pesticides and other toxicants.

Effects of acute exposure to methyl parathion on carbohydrate metabolism of Indian catfish (Heteropneustes fossilis).

Exposure of the Indian catfish (Heteropneustes fossilis) to a high sublethal concentration of 5.6 p.p.m. (0.8 of the 96 hr LC50) of methyl parathion for 3, 6, 12, 48, and 96 hrs affected carbohydrate metabolism. Muscle glycogen levels decreased significantly at 3, 6, 12 and 96 hrs; liver glycogen content declined at 6 hrs but there was a resynthesis of hepatic glycogen stores at 12 hrs. Blood glucose levels in fish were elevated at 3 and 6 hrs. Mean values for blood pyruvate were elevated significantly at 6, 12, and 96 hrs. Blood lactate level was elevated at 3 hrs but hypolactaemia resulted at 48 and 96 hrs in pesticide-treated fish. The observed effects of methyl parathion on carbohydrate metabolism in fish are discussed in relation to acute stress syndrome. Measurement of carbohydrate metabolites in fish for 3 hrs or longer could prove useful as a rapid method for evaluating toxicity of pesticides and other toxicants.

A Comparative Study of Carbohydrate Metabolism in Fish as Affected by Temperature and Exercise

A Comparative Study of Carbohydrate Metabolism in Fish as Affected by Temperature and Exercise