Animal models of human amino acid responses

Regulation of amino acid metabolism in Aphis gossypii parasitized by Binodoxys communis

The vast majority of parasitoids are capable of precise and meticulous regulation of nutrition and metabolism within the host. An important building block of life, amino acids are critical to the development of parasitoids. To date, research on how parasitoids regulate host amino acid metabolism remains limited. In this study, Aphis gossypii and its dominant parasitoid Binodoxys communis were used as a study system to explore how parasitism may change the regulation of amino acids in A. gossypii with UHPLC-MS/MS and RT-qPCR techniques. Here, for the first 8 h of parasitism the abundance of almost all amino acids in cotton aphids increased, and after 16 h most of the amino acids decreased. An amino acid of parasitic syndrome, the content of Tyr increased gradually after being parasitized. The expression of genes related to amino acid metabolism increased significantly in early stages of parasitism and then significantly decreased gradually. At the same time, the abundance of Buchnera, a cotton aphid specific symbiont increased significantly. Our comprehensive analyses reveal impacts of B. communis on the amino acid regulatory network in cotton aphid from three aspects: amino acid metabolism, gene expression, and bacterial symbionts. Therefore, this research provides an important theoretical basis for parasitoid nutritional regulation in host, which is highly significant as it may inform the artificial reproduction of parasitoids and the biological control of insect pests.

Flash dietary methionine supply over growth requirements in pigs: Multi-facetted effects on skeletal muscle metabolism

Dietary methionine affects protein metabolism, lean gain and growth performance and acts in the control of oxidative stress. When supplied in large excess relative to growth requirements in diets for pigs, positive effects on pork quality traits have been recently reported. This study aimed to decipher the molecular and biochemical mechanisms affected by a dietary methionine supply above growth requirements in the loin muscle of finishing pigs. During the last 14 days before slaughter, crossbred female pigs (n = 15 pigs/diet) were fed a diet supplemented with hydroxy-methionine (Met5; 1.1% of methionine) or not (CONT, 0.22% of methionine). Blood was sampled at slaughter to assess key metabolites. At the same time, free amino acid concentrations and expression or activity levels of genes involved in protein or energy metabolism were measured in the longissimus lumborum muscle (LM). The Met5 pigs exhibited a greater activity of creatine kinase in plasma when compared with CONT pigs. The concentrations of free methionine, alpha-aminobutyric acid, anserine, 3-methyl-histidine, lysine, and proline were greater in the LM of Met5 pigs than in CONT pigs. Expression levels of genes involved in protein synthesis, protein breakdown or autophagy were only scarcely affected by the diet. Among ubiquitin ligases, MURF1, a gene known to target creatine kinase and muscle contractile proteins, and OTUD1 coding for a deubiquitinase protease, were up-regulated in the LM of Met5 pigs. A lower activity of citrate synthase, a reduced expression level of ME1 acting in lipogenesis but a higher expression of PPARD regulating energy metabolism, were also observed in the LM of Met5 pigs compared with CONT pigs. Principal component analysis revealed that expression levels of many studied genes involved in protein and energy metabolism were correlated with meat quality traits across dietary treatments, suggesting that subtle modifications in expression of those genes had cumulative effects on the regulation of processes leading to the muscle transformation into meat. In conclusion, dietary methionine supplementation beyond nutritional requirements in pigs during the last days before slaughter modified the free amino acid profile in muscle and its redox capacities, and slightly affected molecular pathways related to protein breakdown and energy metabolism. These modifications were associated with benefits on pork quality traits.

Safety and efficacy of l-arginine produced by fermentation using Corynebacterium glutamicum KCCM 10741P for all animal species

l-Arginine is considered to be a non-essential amino acid for most adult mammalian species, but it is classified as essential for birds, fish, possibly reptiles and also for strict carnivores. The product subject of this assessment is l-arginine produced by fermentation using a non-genetically modified strain of Corynebacterium glutamicum (KCCM 10741P). It is intended to be used in feed and water for drinking for all animal species and categories. Species identity of the production organism was confirmed and the strain was sensitive to antibiotics at concentrations at or below thresholds specified by EFSA; thus, C. glutamicum KCCM 10741P may be considered safe by the qualified presumption of safety (QPS) approach. No viable cells of C. glutamicum were detected in the final product. The amount of identified material exceeded 99.8%, and no impurities of concern were detected. The use of l-arginine produced by C. glutamicum KCCM 10741P is safe for target species when supplemented to diets in appropriate amounts, for the consumer and the environment. l-Arginine produced by C. glutamicum KCCM 10741P is considered corrosive to skin and eyes and therefore poses a risk by inhalation. The additive is an effective source of arginine for all species. For the supplemental l-arginine to be as efficacious in ruminants as in non-ruminant species, it requires protection against microbial degradation in the rumen.

Safety and efficacy of l-arginine produced by fermentation with Escherichia coli NITE BP-02186 for all animal species

l-Arginine is considered as a non-essential amino acid for most adult mammalian species, but it is classified as essential for birds, fish, possibly reptiles and also for strict carnivores. l-Arginine produced by fermentation with Escherichia coli NITE BP-02186, genetically modified to enhance the production of l-arginine, is intended to be used in feed and water for drinking for all animal species and categories. The product under assessment does not give rise to any safety concern with regard to the genetic modification of the production strain. Its use as a nutritional additive is safe for target species when supplemented to diets in appropriate amounts. The use of l-arginine as a feed flavouring agent is unlikely to pose any concern. No risks are expected for the consumer from the use of the product under assessment as a feed additive. It is not irritant to skin or eyes, nor a skin sensitiser. Although the presence of endotoxin activity is of no concern, the available exposure and toxicological data indicate that the additive may pose a risk to users by inhalation. The use of this additive in animal nutrition does not pose a risk to the environment. The additive is an effective source of arginine for all species. l-Arginine is considered efficacious when used as a flavouring compound in animal nutrition.

Safety and efficacy of l-arginine produced by Corynebacterium glutamicum KCCM 80099 for all animal species

l-Arginine is considered as a non-essential amino acid for most adult mammalian species, but it is classified as essential for birds, fish, possibly reptiles and also for strict carnivores. The product subject of this assessment is l-arginine produced by fermentation with a genetically modified strain of Corynebacterium glutamicum (KCCM 80099). It is intended to be used in feed and water for drinking for all animal species and categories. The following conclusions refer to the additive 'L-arginine produced by Corynebacterium glutamicum KCCM 80099'. Neither the genetically modified production strain nor its recombinant DNA were detected in the final product. The additive does not give rise to safety concerns with regard to the genetic modification of the production strain. The use of the additive is safe for target species when supplemented to diets in appropriate amounts, for the consumer and for the environment. The additive is not hazardous by inhalation, is not a skin sensitiser, but is corrosive to skin and eyes. The additive is an effective source of arginine for all species. For the supplemental l-arginine to be as efficacious in ruminants as in non-ruminant species, it requires protection against microbial degradation in the rumen.

Changes in the amount of lysine in protective proteins and immune cells after a systemic response to dead Escherichia coli: implications for the nutritional costs of immunity

The nutritional demands of the immune system may result in tradeoffs with competing processes such as growth and reproduction. The magnitude of the nutritional costs of immunity is largely unknown. Thus, we examine the lysine content of the systemic components of the immune system in adult male chickens (Gallus gallus domesticus) in a healthy condition (maintenance) and following a robust Escherichia coli-specific immune response. Lysine was used as a metric, because it is found both in leukocytes and in protective proteins. The dynamics of subsets of leukocytes were monitored in primary and secondary immune tissues (thymus, bone marrow, and spleen) that would be expected to be involved in the response following iv injection of E. coli. The systemic immune system at maintenance has the same lysine content as 332 average-sized feathers, 16% of an egg, or 5.4% of a pectoralis muscle from an adult chicken. During the acute-phase response to E. coli, the additional lysine needed would equal 355 feathers, 17% of an egg, or 5.5% of a pectoralis muscle. The acute-phase proteins accounted for the greatest proportion of lysine in the immune system at maintenance and the proportion increased substantially during an acute-phase response. Hypertrophy of the liver required more lysine than all of the leukocytes and protective proteins that were produced during the acute-phase response. Size of the liver and levels of protein during the acute phase returned to normal during the time when the adaptive response began to utilize significant quantities of lysine. The catabolism would release a surfeit of lysine to provision the anabolic processes of the adaptive response, thus making proliferation of lymphocytes and production of immunoglobulins very cheap.

Response of European sea bass (Dicentrarchus labrax) to graded levels of methionine (total sulfur amino acids) in soya protein-based semi-purified diets

The dietary methionine (Met) and total sulfur amino acid (TSAA) requirements of European sea bass (Dicentrarchus labrax) (initial body weight 13·4 (sd 0·2) g) were estimated in a 12-week dose–response experiment. Seven isonitrogenous (7·6 % DM) and isoenergetic (gross energy, 21·2 MJ/kg DM) diets, based on soya protein and crystalline l-amino acids containing graded levels of l-Met (1·6–16·2 g/kg) at a constant cysteine (4 g/kg) level and a fish meal-based diet, were fed each to triplicate groups of fifty fish kept in 250 litre tanks in a thermoregulated (23 ± 0·5°C) seawater system. The Met and TSAA-deficient diet resulted in higher mortality, impaired feed intake and growth relative to the other treatments (P < 0·01). No signs of lens opacity due to limiting Met intake were observed and no feed intake or growth depression occurred at the highest level of dietary TSAA. Met and TSAA requirements for optimal N deposition or weight gain as fitted with the broken-line model resulted in estimated values of 8·0 and 12·0 g/kg diet (for example, 1·8 and 2·7 % dietary protein) and 9·1 and 13·1 g/kg diet (for example, 2·0 and 3·0 % dietary protein), respectively. Plasma levels of Met, homocysteine and cysteine increased in response to excess dietary TSAA, corroborating requirement estimates from growth data. N gain resulted in a linear function of TSAA consumption at marginal Met (TSAA) intake. The TSAA intake needed to maintain N balance resulted in a value of 20·0 mg TSAA/kg average body weight0·75 per d, which represents 23 % of the total (maintenance+accretion) requirement.

Dietary supplementation of glycine modulates inflammatory response indicators in broiler chickens

Three experiments were conducted to investigate the effect of dietary glycine (Gly) supplementation on inflammatory responses in broiler chicks fed a basal diet using maize and soyabean meal as the primary ingredients. Inflammation-related processes following lipopolysaccharide (LPS) injection were examined by analysing plasma concentrations of nitrate plus nitrite (NOx) and ceruloplasmin (Cer) in experiments 1 and 2, or expression of several genes in the spleen and liver including IL-1β and -6, TNF-like ligand (TL)1A, inducible NO synthase, interferon (IFN)-γ and toll-like receptor (TLR) 4 were examined in experiment 3. Growth performance was also determined following immunological stimulation by both LPS and Sephadex injection in experiment 2. In experiment 1, birds fed a diet supplemented with Gly at 10 or 20 g/kg showed lower responses in plasma NOx and Cer than birds fed the diet supplemented with Gly at 0 or 40 g/kg. In experiment 2, a similar effect of Gly supplementation at 10 g/kg on plasma NOx and Cer was observed when chicks were fed either an isonitrogenous diet with Gly or glutamic acid (Glu). Gly-supplemented diet-fed birds showed better growth performance than Glu-supplemented diet-fed birds. The splenic expression of inflammatory response-related genes in birds fed a diet supplemented with Gly at 10 g/kg diet was lower than that of birds fed the basal diet in experiment 3. These results suggest that dietary Gly supplementation modulates the inflammatory response partly through changes in the expression of pro-inflammatory cytokines such as IL-1, IL-6, IFN-γ and TL1A.

Pharmacokinetics and safety of arginine supplementation in animals

Anticipating the future use of arginine to enhance fetal and neonatal growth as well as to treat diabetes and obesity, we performed studies in pigs, rats, and sheep to determine the pharmacokinetics of orally or i.v. administered arginine and the safety of its chronic supplementation. Our results indicate that all 3 species rapidly catabolized the supplemental arginine. The elevated circulating concentrations of arginine generally returned to baseline levels within 4-5 h after administration, with the rates varying with the age and physiological status of the animals. The clearance of arginine was greater in pregnant than in nonpregnant animals, in young than in adult animals, in lean than in obese animals, and in type-1 diabetic than in nondiabetic animals. I.v. administration of arginine-HCl to pregnant ewes (at least 0.081 g arginine.kg body weight-1.d-1) did not result in any undesirable treatment-related effect. Neonatal pigs, growing-finishing pigs, pregnant pigs, and adult rats tolerated large amounts of chronic supplemental arginine (e.g. 0.62, 0.32, 0.21, and 2.14 g.kg body weight-1.d-1, respectively) administered via enteral diets without the appearance of any adverse effect. On the basis of the comparative studies and a consideration of species differences in food intake per kilogram body weight, we estimate that a 70-kg human subject should be able to tolerate long-term parenteral and enteral supplemental doses of 6 and 15 g/d arginine, respectively, in addition to a basal amount of arginine (4-6 g/d) from regular diets.

Contribution of research with farm animals to protein metabolism concepts: a historical perspective

The roles of proteins, carbohydrates, fats, and micronutrients in animal and human nutrition were broadly described during the late 18th and 19th centuries, and knowledge in protein nutrition evolved from work with all species. Although much of the fundamental and theoretical research in protein metabolism during the 20th century was conducted with laboratory animals, basic protein nutrition research in farm animals complemented those efforts and led to the development and use of new investigative methods (particularly in amino acid nutrition) as well as use of animal models in furthering the understanding of human protein metabolism. All these efforts have led to a contemporary hybrid model of protein nutrition and metabolism applicable to both humans and animal species. Now in the 21st century, farm animals are used in fetal and pediatric nutrition research, and data accruing for excess amino acid feeding in research with farm animals provide direction for assessment of pharmacological effects of amino acids when consumed in excessive quantities. Thus, as nutritional science is moving forward into nutrigenomics, nutriproteomics, and metabolomics, farm animal and human nutrition research interactions will likely continue with genetically modified farm animals produced for agricultural reasons (improved function and product quality) or those produced with human genes introduced to generate even better models of human protein metabolism.

Efficiency of methionine retention in ducks

The accretion of methionine and protein as a function of methionine intake was assessed in growing ducks between 22 and 42 d post-hatching. Four graded doses of dl-methionine at 0, 0·5, 1·0 or 1·5 g/kg diet were added to a methionine-limiting basal diet and fed to four replicate groups of four ducks each. The growth and efficiency of food use for growth increased linearly (P < 0·05) as a function of methionine intake. The accretion of body protein increased (P < 0·001) from 87·5 to 182·2 g, and that of methionine from 1616 to 3125 mg, over the 21 d period as dietary methionine increased. The accretion rate of methionine in the body (y, mg/d) as a function of methionine intake (x, mg/d) of ducks fed diets containing supplemental methionine at 0, 0·5, 1·0 or 1·5 g/kg diet from day 22 to day 42 post-hatching gave the regression equation: y = − 148·86 (se 32·558)+0·312 (se 0·0384)X, r2 = 0·8253. For protein accretion rate in the body (y, mg/d) as a function of methionine intake (x, mg/d), the regression equation was: y = − 9782 (se 2204)+19·505 (se 2·5994)x, r2 = 0·8009. There was a linear relationship between methionine (y, mg/d) and protein (x, mg/d) accretion in ducks that was described by the equation y = 12·757 (se 7·4019)+0·01 525 (se 0·00 107)x, r2 = 0·9355. The results of these studies suggest a constant utilisation of methionine over the range 2·4–3·9 g digestible methionine/kg diet, with an efficiency of 31 %. Furthermore, the results suggest a quantitative relationship of 15 mg methionine for every gram of protein accretion.

Comparative nutrition and metabolism: explication of open questions with emphasis on protein and amino acids

The 20th century saw numerous important discoveries in the nutritional sciences. Nonetheless, many unresolved questions still remain. Fifteen questions dealing with amino acid nutrition and metabolism are posed in this review. The first six deal with the functionality of sulfur amino acids (methionine and cysteine) and related compounds. Other unresolved problems that are discussed include priorities of use for amino acids having multiple functions; interactions among lysine, niacin and tryptophan; amino acid contributions to requirements from gut biosynthesis; the potential for gluconeogenesis to divert amino acids away from protein synthesis; the unique nutritional and metabolic idiosyncrasies of feline species, with emphasis on arginine; controversies surrounding human amino acid requirements; and the potential for maternal diet to influence sex ratio of offspring.

Tolerance for branched-chain amino acids in experimental animals and humans

There is no good evidence for establishing branched-chain amino acid (BCAA) tolerance levels for humans. With pigs, chicks, and rats, data are available concerning excessive intake levels of BCAA, but most of the information is for growing animals instead of for adults. Estimates of maintenance requirements for (high-quality) protein and BCAA in pigs weighing between 43 and 140 kg are 350 mg . kg(-1) . d(-1) for protein and 28.7 mg . kg(-1) . d(-1) for total BCAA. In contrast, human adult maintenance requirement estimates are much higher, i.e., 660 mg . kg(-1) . d(-1) for good quality protein and a range of 68 to 144 mg . kg(-1) . d(-1) for total BCAA. The human maintenance BCAA requirement estimates range from 10.3 to 22% of the maintenance protein requirement. Whole-body protein of 45-kg pigs contains 14.2 g BCAA/100 g protein, but the maintenance requirement (based on nitrogen balance) for total BCAA is only 8.2% of the total maintenance protein requirement. Conversely, sulfur amino acid (methionine + cysteine), threonine, and tryptophan maintenance requirements of pigs as a percentage of the maintenance protein requirement are much higher than whole-body protein levels of these amino acids. This suggests that the efficiency of using absorbed amino acids of dietary origin or of reusing endogenous amino acids arising from body protein catabolism may vary considerably among the indispensable amino acids. Additionally, work with pigs points to the conclusion that whole-body amino acid concentrations are poor predictors of both maintenance requirements and ideal amino acid profiles. Based on studies with young experimental animals, a rather large dietary excess (above requirement) of an individual BCAA is well tolerated when consumed in diets containing surfeit levels of protein and the other 2 BCAA.