Adaptable hexokinase with low affinity for glucose in the liver of atlantic salmon (Salmo salar)

Effects of Dietary Multienzyme Complex Supplementation on Growth Performance, Digestive Capacity, Histomorphology, Blood Metabolites and Hepatic Glycometabolism in Snakehead (Channa argus)

Simple Summary

The multienzyme complex is composed of one or several single enzymes as the main component, mixed with other single enzyme preparations, or obtained by the fermentation of one or more microorganisms, and an the exogenous enzyme mixture with multiple functions of a single enzyme. Supplementation with exogenous enzyme preparations offsets the negative effects of removing antibiotics from animal diets. The multienzyme complex supplemented in aquatic feed can enhance the secretion and activity of endogenous digestive enzymes in aquatic animals. Meanwhile, exogenous digestive enzymes can also help aquatic animals to decompose some anti-nutrients, improve the utilization and digestibility of feed, and promote animal growth.

Abstract

The present study evaluated the impact of dietary multienzyme complex (MEC) supplementation on growth performance, digestive enzyme activity, histomorphology, serum metabolism and hepatopancreas glycometabolism in snakeheads (Channa argus). A total of 600 fish (initial weight, 69.70 ± 0.30 g) were randomly divided into four groups. Four diets were formulated: (1) control (basic diet); (2) E1 (400 U kg⁻¹ amylase, 150 U kg⁻¹ acid protease, 1900 U kg⁻¹ neutral protease and basic diet); (3) E2 (800 U kg⁻¹ amylase, 300 U kg⁻¹ acid protease, 3800 U kg⁻¹ neutral protease and basic diet); and (4) E3 (1200 U kg⁻¹ amylase, 450 U kg⁻¹ acid protease, 5700 U kg⁻¹ neutral protease and basic diet). The results show that the E2 group increased the specific growth rate, weight gain rate and the final body weight, as well as decreasing the blood urea nitrogen, alanine aminotransferase and triglyceride. The mRNA levels and activities of digestive enzymes and key glucose metabolism enzymes in the hepatopancreas were enhanced in snakeheads fed the MEC. Meanwhile, moderate MEC diet (E2 groups) supplementation improved digestive tract morphology, increased the glycogen in the hepatopancreas and the lipids in the dorsal muscle. Moreover, plasma metabolomics revealed differential metabolites mainly involved in amino acid metabolism. These findings suggest that dietary supplementation with the MEC improved growth performance, digestive tract morphology, gene expression and the activity of digestive enzymes, enhanced the glycolysis-gluconeogenesis and amino acid metabolism of snakeheads, and the optimal composition of the MEC was group E2.

Long-term feeding a plant-based diet devoid of marine ingredients strongly affects certain key metabolic enzymes in the rainbow trout liver

Incorporation of a plant blend in the diet can affect growth parameters and metabolism in carnivorous fish. We studied for the first time the long-term (1 year) metabolic response of rainbow trout fed from first feeding with a plant-based diet totally devoid of marine ingredients. Hepatic enzymes were analyzed at enzymatic and molecular levels, at 3, 8 and 24 h after the last meal to study both the short-term effects of the last meal and long-term effects of the diet. The results were compared with those of fish fed a control diet of fish meal and fish oil. Growth, feed intake, feed efficiency and protein retention were lower in the group fed the plant-based diet. Glucokinase and pyruvate kinase activity were lower in the livers of trout fed the plant-based diet which the proportion of starch was lower than in the control diet. Glutamate dehydrogenase was induced by the plant-based diet, suggesting an imbalance of amino acids and a possible link with the lower protein retention observed. Gene expression of delta 6 desaturase was higher in fish fed the plant-based diet, probably linked to a high dietary level of linolenic acid and the absence of long-chain polyunsaturated fatty acids in vegetable oils. Hydroxymethylglutaryl-CoA synthase expression was also induced by plant-based diet because of the low rate of cholesterol in the diet. Changes in regulation mechanisms already identified through short-term nutritional experiments (<12 weeks) suggest that metabolic responses are implemented at short term and remain in the long term.

Comparison of glucose and lipid metabolic gene expressions between fat and lean lines of rainbow trout after a glucose load

Two experimental rainbow trout lines developed through divergent selection for low (Lean ‘L’ line) or high (Fat ‘F’ line) muscle fat content were used as models to study the genetic determinism of fat depots. Previous nutritional studies suggested that the F line had a better capability to use glucose than the L line during feeding trials. Based on that, we put forward the hypothesis that F line has a greater metabolic ability to clear a glucose load effectively, compared to L line. In order to test this hypothesis, 250 mg/kg glucose was intraperitoneally injected to the two rainbow trout lines fasted for 48 h. Hyperglycemia was observed after glucose treatment in both lines without affecting the phosphorylation of AMPK (cellular energy sensor) and Akt-TOR (insulin signaling) components. Liver glucokinase and glucose-6-phosphate dehydrogenase expression levels were increased by glucose, whereas mRNA levels of β-oxidation enzymes (CPT1a, CPT1b, HOAD and ACO) were down-regulated in the white skeletal muscle of both lines. Regarding the genotype effect, concordant with normoglycemia at 12 h after glucose treatment, higher muscle glycogen was found in F line compared to L line which exhibited hyperglycemia. Moreover, mRNA levels of hepatic glycolytic enzymes (GK, 6PFK and PK), gluconeogenic enzyme PEPCK and muscle fatty acid oxidation enzymes (CPT1a, CPT1b and HOAD) were concurrently higher in the F line. Overall, these findings suggest that F line may have a better ability to maintain glucose homeostasis than L line.

Nutritional regulation of glucokinase: a cross-species story

The glucokinase (GK) enzyme (EC 2.7.1.1.) is essential for the use of dietary glucose because it is the first enzyme to phosphorylate glucose in excess in different key tissues such as the pancreas and liver. The objective of the present review is not to fully describe the biochemical characteristics and the genetics of this enzyme but to detail its nutritional regulation in different vertebrates from fish to human. Indeed, the present review will describe the existence of the GK enzyme in different animal species that have naturally different levels of carbohydrate in their diets. Thus, some studies have been performed to analyse the nutritional regulation of the GK enzyme in humans and rodents (having high levels of dietary carbohydrates in their diets), in the chicken (moderate level of carbohydrates in its diet) and rainbow trout (no carbohydrate intake in its diet). All these data illustrate the nutritional importance of the GK enzyme irrespective of feeding habits, even in animals known to poorly use dietary carbohydrates (carnivorous species).

Improving estimates of trophic shift in Nile tilapia, Oreochromis niloticus (L.), using measurements of lipogenic enzyme activities in the liver

To test whether the measurement of selected enzyme activities could be used to estimate more precisely the trophic shift of C isotopes, Nile tilapia (Oreochromis niloticus) were fed semi-synthetic diets differing in their lipid contents (1.7%, 5.0%, 10.8% and 20.0%). The diets were formulated to contain the same amount of nitrogen and metabolizable energy and were made from casein, wheat starch, corn germ oil supplemented with vitamins, minerals and L-arginine. The influence of the different diets on the activity of two lipogenic enzymes, ATP-citrate lyase and malic enzyme, on delta13C values in the whole fish, the liver and their correlation was investigated. There was a strong positive correlation between delta13C values in the lipids of whole fish and those of their livers. The activities of lipogenic enzymes increased significantly with increasing trophic shift of C isotopes (Deltadelta13Cdiet-fish values) in the lipids. If the relationship between trophic shift and enzyme activity can be confirmed in situations where feed quantity and quality are not known, the determination of enzyme activities would enable better estimates of the trophic shift to be made thus significantly improving back-calculation of diets from stable isotope data.

D-Glucose uptake in fish hepatocytes: mediated by transporter in rainbow trout (Oncorhynchus mykiss), but only by diffusion in prespawning lamprey (Lampetra fluviatilis) and in RTH-149 cell line

The transport of D-glucose into rainbow trout (Oncorhynchus mykiss) and river lamprey (Lampetra fluviatilis) hepatocytes, as well as into rainbow trout hepatoblastoma cell line RTH-149 was studied using tracer methods. The half-time for D-glucose equilibration was 15 s for rainbow trout. The half-times for the non-metabolizable D-glucose analog, 3-O-methyl-D-glucose equilibration were 8 s, 37 s and 38 s for rainbow trout, lamprey and RTH-149 cells, respectively. The 3-O-methyl-D-glucose was taken up by rainbow trout hepatocytes by facilitated diffusion in addition to simple diffusion. The uptake showed saturation kinetics with the K(m) of 37 mM and V(max) of 62 mmol kg(-1) cells min(-1). The uptake was sensitive to phloretin and cytochalasin B, but not affected by ouabain. The 3-O-methyl-D-glucose uptake by lamprey hepatocytes and RTH-149 cells showed no indication of saturation up to 160 mM, and was not affected by phloretin, cytochalasin B or ouabain, which suggests the mode of transport to be by passive diffusion. However, immunocytochemical stainings revealed the existence of mammalian type GLUT1 and GLUT2 transporters in all cells studied. The lack of a functioning carrier-mediated glucose uptake in lamprey hepatocytes might be due to its physiological state (prespawning starvation). The minor 3-O-methyl-D-glucose uptake into RTH-149 cells compared to freshly isolated rainbow trout hepatocytes might reflect low metabolic activity of the cell lines. Under the conditions applied the RTH-149 cell line is no suitable in vitro model for glucose transport in fish cells.