The effect of ketone bodies on protein turnover in isolated skeletal muscle from the fed and fasted chick

Protein-Sourced Feedstuffs for Aquatic Animals in Nutrition Research and Aquaculture

Aquatic animals have particularly high requirements for dietary amino acids (AAs) for health, survival, growth, development, and reproduction. These nutrients are usually provided from ingested proteins and may also be derived from supplemental crystalline AA. AAs are the building blocks of protein (a major component of tissue growth) and, therefore, are the determinants of the growth performance and feed efficiency of farmed fish. Because protein is generally the most expensive ingredient in aqua feeds, much attention has been directed to ensure that dietary protein feedstuff is of high quality and cost-effective for feeding fish, crustaceans, and other aquatic animals worldwide. Due to the rapid development of aquaculture worldwide and a limited source of fishmeal (the traditionally sole or primary source of AAs for aquatic animals), alternative protein sources must be identified to feed aquatic animals. Plant-sourced feedstuffs for aquatic animals include soybean meal, extruded soybean meal, fermented soybean meal, soybean protein concentrates, soybean protein isolates, leaf meal, hydrolyzed plant protein, wheat, wheat hydrolyzed protein, canola meal, cottonseed meal, peanut meal, sunflower meal, peas, rice, dried brewers grains, and dried distillers grains. Animal-sourced feedstuffs include fishmeal, fish paste, bone meal, meat and bone meal, poultry by-product meal, chicken by-product meal, chicken visceral digest, spray-dried poultry plasma, spray-dried egg product, hydrolyzed feather meal, intestine-mucosa product, peptones, blood meal (bovine or poultry), whey powder with high protein content, cheese powder, and insect meal. Microbial sources of protein feedstuffs include yeast protein and single-cell microbial protein (e.g., algae); they have more balanced AA profiles than most plant proteins for animal feeding. Animal-sourced ingredients can be used as a single source of dietary protein or in complementary combinations with plant and microbial sources of proteins. All protein feedstuffs must adequately provide functional AAs for aquatic animals.

Anabolic effects of oral leucine-rich protein with and without β-hydroxybutyrate on muscle protein metabolism in a novel clinical model of systemic inflammation-a randomized crossover trial

BACKGROUND

β-lactoglobulin (BLG) stimulates muscle protein synthesis and β-hydroxybutyrate (BHB) inhibits muscle breakdown. Whether combining the 2 can additively attenuate disease-induced muscle loss is unknown.

OBJECTIVE

Based on previous observations of anticatabolic effects of protein and ketone bodies during inflammation, and using a novel model combining ongoing systemic inflammation, fasting, and immobilization, we tested whether the anticatabolic muscle response to oral amino acids is altered compared with control conditions, as well as whether coadministration of oral BHB and BLG further improves the muscle anabolic response. Muscle net balance (NBphe) was the primary outcome and intramyocellular signals were assessed.

METHODS

In a randomized crossover design, 8 young men underwent either preconditioning with LPS (prestudy day: 1 ng/kg, study day: 0.5 ng/kg) combined with a 36-h fast and bed rest to mimic catabolic inflammatory disease (CAT) or an overnight fast (control [CTR]) prior to isocaloric nutritional interventions on 3 occasions separated by ∼6 wk (range 42 to 83 d).

RESULTS

NBphe increased similarly upon all conditions (interaction P = 0.65). From comparable baseline rates, both Rdphe [muscle synthesis, median ratio (95% CI): 0.44 (0.23, 0.86) P = 0.017] and Raphe [muscle breakdown, median ratio (95% CI): 0.46 (0.27, 0.78) P = 0.005] decreased following BHB + BLG compared with BLG. BLG increased Rdphe more under CAT conditions compared with CTR (interaction P = 0.02). CAT increased inflammation, energy expenditure, and lipid oxidation and decreased Rdphe and anabolic signaling [mammalian target of rapamycin (mTOR) and eukaryotic translation initiation factor 4E-binding protein 1 (4EPB1) phosphorylation].

CONCLUSION

In contrast to our initial hypothesis, NBphe increased similarly following BLG during CAT and CTR conditions; CAT however, specifically stimulated the BLG-mediated increase in protein synthesis, whereas BHB coadministration did not affect NBphe, but distinctly dampened the BLG-induced increase in muscle amino acid fluxes thereby liberating circulating amino acids for anabolic actions elsewhere.

Intake of a Ketone Ester Drink during Recovery from Exercise Promotes mTORC1 Signaling but Not Glycogen Resynthesis in Human Muscle

Purpose: Ketone bodies are energy substrates produced by the liver during prolonged fasting or low-carbohydrate diet. The ingestion of a ketone ester (KE) rapidly increases blood ketone levels independent of nutritional status. KE has recently been shown to improve exercise performance, but whether it can also promote post-exercise muscle protein or glycogen synthesis is unknown. Methods: Eight healthy trained males participated in a randomized double-blind placebo-controlled crossover study. In each session, subjects undertook a bout of intense one-leg glycogen-depleting exercise followed by a 5-h recovery period during which they ingested a protein/carbohydrate mixture. Additionally, subjects ingested a ketone ester (KE) or an isocaloric placebo (PL). Results: KE intake did not affect muscle glycogen resynthesis, but more rapidly lowered post-exercise AMPK phosphorylation and resulted in higher mTORC1 activation, as evidenced by the higher phosphorylation of its main downstream targets S6K1 and 4E-BP1. As enhanced mTORC1 activation following KE suggests higher protein synthesis rates, we used myogenic C₂C₁₂ cells to further confirm that ketone bodies increase both leucine-mediated mTORC1 activation and protein synthesis in muscle cells. Conclusion: Our results indicate that adding KE to a standard post-exercise recovery beverage enhances the post-exercise activation of mTORC1 but does not affect muscle glycogen resynthesis in young healthy volunteers. In vitro, we confirmed that ketone bodies potentiate the increase in mTORC1 activation and protein synthesis in leucine-stimulated myotubes. Whether, chronic oral KE intake during recovery from exercise can facilitate training-induced muscular adaptation and remodeling need to be further investigated.

Effect of energy substrates on protein degradation in isolated small intestinal enterocytes from rats

BACKGROUND

Nutrients affect small intestinal protein mass and metabolism, but studies on the effect of nutrients on small intestinal protein degradation are very limited due to a lack of a proper method. The objectives of this study were to establish a method to directly estimate protein degradation in isolated enterocytes from rats and to test the effect of energy substrates on protein degradation.

METHODS

Male Sprague-Dawley rats (150-200 g, n>or=8 per treatment) were used. Cell viability, tyrosine release as an indicator of protein degradation, and the effect of osmolarity, 50 mmol/L glucose, 20 mmol/L beta-hydroxybutyrate, 4.7 mmol/L butyrate, and 30 mmol/L glutamine on protein degradation were measured.

RESULTS

The average viability of enterocytes at time 30 minutes was 85.8% (range, 81%-94%). Tyrosine release was linear over the course of experiments, indicating constant protein degradation (R2=0.9943; p<.05). Osmolarity, glucose, and glutamine had no effect on protein degradation in isolated enterocytes. Beta-hydroxybutyrate significantly decreased it (-16%; p<.05), whereas butyrate slightly increased it (+5%; p<.05).

CONCLUSIONS

A high viability and constant protein degradation indicate a successful establishment of a method to estimate protein degradation in isolated small intestinal enterocytes from rats. The large effect of beta-hydroxybutyrate suggests a potential positive role for ketone bodies to limit the loss of small intestinal protein mass by decreasing protein degradation.

Macrophage population dynamics within fetal mouse fibroblast cultures derived from C57BL/6, CD-1, CF-1 mice and interleukin-6 and granulocyte colony stimulating factor knockout mice

In vitro models of macrophage growth, differentiation, and function are needed to facilitate the study of their biology as important immune facilitator cells and as frequent targets of bacterial and viral infection. A simple method for the selective expansion and continuous culture of mouse macrophages from primary explant cultures of mouse embryonic tissue is described. Culture in Dulbecco modified Eagle medium (DMEM) low-glucose (1 g/L) formulation (DMEM/L) inhibited fibroblast growth. In contrast, macrophages continued to proliferate in the presence of DMEM/L when in contact with the fibroblasts. Alternating growth in high-glucose DMEM with DMEM/L produced a 1.16- to 2.1-fold increase (depending on mouse strain) in the percentage of macrophages within the cell culture in comparison with culturing in DMEM with high glucose exclusively. Macrophage yields of over 1 million cells/T12.5 flask were achieved by passages 3-4, and, thereafter, declined over the next 5-10 passages. The peak percentage of macrophages within a culture varied depending on the strain of mouse (C57BL/6, CD-1, and CF-1 and two knockout C57BL/6 strains deficient in either interleukin-6 [IL-6] or granulocyte colony stimulating factor [GCSF]). The GCSF (-/-)-derived cultures had the lowest peak macrophage content (30%) and CD-1 the highest content (64.9%). The IL-6 (-/-) and CD-1 cultures appeared to spontaneously transform to create cell lines (IL6MAC and CD1MAC, respectively) that were composed of 50-75% macrophages. The macrophages were phagocytic and were positive for CD14, acetylated low-density lipoprotein receptors, and F4-80 antigen. Light and electron microscopy showed that the cultured macrophages had in vivo-like morphological features, and they could be plated to high purity by differential attachment to petri dishes in serum-free medium.

High beta-hydroxybutyrate concentration in liver and skeletal muscle of newly hatched chicks

Characteristic changes in ketone body concentrations in blood, liver, and skeletal muscle were investigated in detail in newly hatched chicks. The concentration of beta-hydroxybutyrate in the blood was maximal at hatch (0 day), markedly decreased to 3 days, then maintained at low levels, up to 14 days of age. The concentration of acetoacetate in blood, on the other hand, did not change after hatching but remained lower than that of beta-hydroxybutyrate at all ages. In liver and muscles, the concentration of beta-hydroxybutyrate changed in a manner similar to that in the blood. The muscle to blood ratio of the beta-hydroxybutyrate concentration on days -1 and 0 was significantly higher than those at 1 through 14 days post-hatch. These results show that newly hatched chicks have the same high ketone body concentrations in the skeletal muscle, blood and liver. It is, hence, suggested that uptake of beta-hydroxybutyrate by muscles is substantial or that ketogenesis, if any, occurs in muscles immediately before and after hatching of chicks.

Lipolytic and metabolic response to glucagon in fasting king penguins: phase II vs. phase III

This study aims to determine how glucagon intervenes in the regulation of fuel metabolism, especially lipolysis, at two stages of a spontaneous long-term fast characterized by marked differences in lipid and protein availability and/or utilization (phases II and III). Changes in the plasma concentration of various metabolites and hormones, and in lipolytic fluxes as determined by continuous infusion of [2-3H]glycerol and [1-14C]palmitate, were examined in vivo in a subantarctic bird (king penguin) before, during, and after a 2-h glucagon infusion. In the two fasting phases, glucagon infusion at a rate of 0.025 microg. kg(-1). min(-1) induced a three- to fourfold increase in the plasma concentration and in the rate of appearance (Ra) of glycerol and nonesterified fatty acids, the percentage of primary reesterification remaining unchanged. Infusion of glucagon also resulted in a progressive elevation of the plasma concentration of glucose and beta-hydroxybutyrate and in a twofold higher insulinemia. These changes were not significantly different between the two phases. The plasma concentrations of triacylglycerols and uric acid were unaffected by glucagon infusion, except for a 40% increase in plasma uric acid in phase II birds. Altogether, these results indicate that glucagon in a long-term fasting bird is highly lipolytic, hyperglycemic, ketogenic, and insulinogenic, these effects, however, being similar in phases II and III. The maintenance of the sensitivity of adipose tissue lipolysis to glucagon could suggest that the major role of the increase in basal glucagonemia observed in phase III is to stimulate gluconeogenesis rather than fatty acid delivery.

The effect of ketone bodies on nitrogen metabolism in skeletal muscle

1. The ketone bodies, D-beta-hydroxybutyrate and acetoacetate, inhibit glycolysis thereby reducing pyruvate availability which leads to a marked inhibition of branched-chain amino acid metabolism and alanine synthesis in skeletal muscles from fasted mammalian and avian species. 2. The rate of glutamine release from skeletal muscles from fasted birds is increased at the expense of alanine in the presence of elevated concentrations of ketone bodies because of an increase in the availability of glutamate for glutamine synthesis. 3. Ketone bodies inhibit both protein synthesis and protein degradation in skeletal muscles from fasted mammalian and avian species in vitro. The mechanisms involved remain unknown. 4. Inhibition of amino acid metabolism and protein turnover in skeletal muscle by ketone bodies may be an important survival mechanism during adaptation to catabolic states such as prolonged fasting.