Effect of different essential amino acid deficiencies on amino acid pools in rats

The human metabolic profile reflects macro- and micronutrient intake distinctly according to fasting time

Although the impact of dietary patterns on human serum metabolites has been examined, the fasting effect on the metabolic profile has not yet been considered. The aim of this cross-sectional study is to investigate the influence of fasting regarding the association between dietary patterns, reflected by macro- and micronutrient intake, and human serum metabolites in a population-based cohort. A total 1197 non-diabetic German adults aged 45 to 83 years, who participated in baseline of the CARLA study 2002–2006 and had metabolite quantification were selected for this study. Macro- and micronutrient intakes were estimated from a food frequency questionnaire (FFQ). Concentrations of 134 serum metabolites were measured by targeted metabolomics AbsoluteIDQ p150 Kit. The association of dietary patterns with serum metabolites was calculated by means of linear regression and the influence of the fasting status was considered by including interaction terms with each macro- and micronutrient. Higher self-reported intake of alcohol and lower self-reported intake of organic acids were associated with higher concentrations of acylcarnitines and phosphatidylcholines. Mainly the associations between dietary patterns and acylcarnitines and hexose were altered after including interaction terms, suggesting effect modification by fasting status. No effect from fasting time was seen for amino acids and saturated, mono- and polyunsaturated phosphatidylcholines.

Leucine Affects α-Amylase Synthesis through PI3K/Akt-mTOR Signaling Pathways in Pancreatic Acinar Cells of Dairy Calves

Dietary nutrient utilization, particularly starch, is potentially limited by digestion in dairy cow small intestine because of shortage of α-amylase. Leucine acts as an effective signal molecular in the mTOR signaling pathway, which regulates a series of biological processes, especially protein synthesis. It has been reported that leucine could affect α-amylase synthesis and secretion in ruminant pancreas, but mechanisms have not been elaborated. In this study, pancreatic acinar (PA) cells were used as a model to determine the cellular signal of leucine influence on α-amylase synthesis. PA cells were isolated from newborn Holstein dairy bull calves and cultured in Dulbecco's modifed Eagle's medium/nutrient mixture F12 liquid media containing four leucine treatments (0, 0.23, 0.45, and 0.90 mM, respectively), following α-amylase activity, zymogen granule, and signal pathway factor expression detection. Rapamycin, a specific inhibitor of mTOR, was also applied to PA cells. Results showed that leucine increased ( p < 0.05) synthesis of α-amylase as well as phosphorylation of PI3K, Akt, mTOR, and S6K1 while reduced ( p < 0.05) GCN2 expression. Inhibition of mTOR signaling downregulated the α-amylase synthesis. In addition, the extracellular leucine dosage significantly influenced intracellular metabolism of isoleucine ( p < 0.05). Overall, leucine regulates α-amylase synthesis through promoting the PI3K/Akt-mTOR pathway and reducing the GCN2 pathway in PA cells of dairy calves. These pathways form the signaling network that controls the protein synthesis and metabolism. It would be of great interest in future studies to explore the function of leucine in ruminant nutrition.

Re-examination of Dietary Amino Acid Sensing Reveals a GCN2-Independent Mechanism

Animals cannot synthesize nine essential amino acids (EAAs) and must therefore obtain them from food. Mice reportedly reject food lacking a single EAA within the first hour of feeding. This remarkable phenomenon is proposed to involve post-ingestive sensing of amino acid imbalance by the protein kinase GCN2 in the brain. Here, we systematically re-examine dietary amino acid sensing in mice. In contrast to previous results, we find that mice cannot rapidly identify threonine- or leucine-deficient food in common feeding paradigms. However, mice attain the ability to identify EAA-deficient food following 2 days of EAA deprivation, suggesting a requirement for physiologic need. In addition, we report that mice can rapidly identify lysine-deficient food without prior EAA deficit, revealing a distinct sensing mechanism for this amino acid. These behaviors are independent of the proposed amino acid sensor GCN2, pointing to the existence of an undescribed mechanism for rapid sensing of dietary EAAs.

The branched-chain amino acid requirement of parenterally fed neonatal piglets is less than the enteral requirement

The requirements for branched-chain amino acids (BCAA), isoleucine, leucine and valine, in neonates have not been determined previously. Furthermore, the BCAA are considered to be catabolized primarily in the muscle and their metabolism in the small intestine has received little attention. In this study, the parenteral and enteral BCAA requirements were determined by the indicator amino acid oxidation (IAAO) technique. Male Yorkshire piglets (n = 32) received amino acid-based diets containing adequate nutrients for 5 d. On d 6 and 8, the piglets were randomly assigned to one of the test diets containing a fixed ratio of BCAA (1:1.8:1.2; isoleucine/leucine/valine). Diets were infused continuously via intravenous catheters for parenterally fed piglets or via gastric catheters for enterally fed piglets. Phenylalanine kinetics and oxidation were determined from a 4-h primed, constant infusion of L-[1-(14)C]phenylalanine. Phenylalanine oxidation (% of dose) decreased linearly (P < 0.05) as the BCAA intake increased from 0.2 to 1.53 g/(kg. d) and from 0.2 to 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively, after which the phenylalanine oxidation was low and the slope was not different from zero. Using breakpoint analysis, the mean total BCAA requirements were determined to be 1.53 and 2.64 g/(kg. d) for parenterally and enterally fed piglets, respectively. Thus, the parenteral requirement for total BCAA is 56% of the enteral requirement, suggesting that 44% of total BCAA is extracted by first-pass splanchnic metabolism.

Deficiency of dietary EAA preferentially inhibits mRNA translation of ribosomal proteins in liver of meal-fed rats

The goal of these studies was to investigate the mechanisms by which amino acid supply regulates global rates of protein synthesis as well as the translation of ribosomal protein (rp) mRNAs in liver. In the experiments conducted, male weanling rats were trained over a 2-wk period to consume their daily food intake within 3 h. On day 14, rats were fed the control diet or an isocaloric, isonitrogenous diet lacking glycine, tryptophan, leucine, or the branched-chain amino acids (BCAA) for 1 h. Feeding Trp-, Leu-, or BCAA-deficient diets resulted in significant reductions in serum insulin, hepatic protein synthesis, eukaryotic initiation factor 2B (eIF2B) activity, and phosphorylation of eIF4E-binding protein 1 (4E-BP1) and ribosomal protein S6 kinase (S6K1). Phosphorylation of eIF2alpha was inversely related to eIF2B activity under all conditions. Alterations in the hepatic synthesis of rp were assessed by changes in the distribution of rp (S4, S8, L26) mRNAs across sucrose density gradients and compared with non-rp (beta-actin, albumin) mRNAs. In all dietary treatments, non-rp mRNAs were mostly polysome associated. Conversely, the proportion of rp mRNAs residing in polysomes was two- to fivefold less in rats fed diets lacking tryptophan, leucine, or BCAA compared with rats fed the control diet. Total hepatic abundance of all mRNAs examined did not differ among treatment groups. For all parameters examined, there were no differences between rats fed the glycine-deficient diet and rats fed the control diet. The data suggest that essential amino acid (EAA) deficiency inhibits global rates of liver protein synthesis via a block in translation initiation. Additionally, the translation of rp mRNAs is preferentially repressed in association with decreased S6K1 phosphorylation.

Amino acid levels in plasma and muscle of rats after intravenous administration of different amino acid infusions

Studies were conducted on the participation of specific amino acids in the alterations of their levels in plasma and muscle of rats after short term intravenous infusion. Sufficient amounts of amino acids and glucose were used as a basal solution, and the levels in plasma and muscle were determined 30 min after the end of infusion. When an infusion solution devoid of one of the essential amino acids from the basal solution, -Leu, -Ile, -Lys or -Thr, was administered, the plasma and muscle levels of the deleted amino acids decreased in different degrees. With infusion of the deficient solutions except for the -Leu, no significant changes were observed in amino acids other than those deleted, although occasional changes were noted. On the other hand, the infusion of the -Leu resulted in significant increase of isoleucine and valine levels, and a moderate increase of many other amino acids both in plasma and in muscle. In contrast, when leucine was administered singly in an amount equivalent to that in the basal solution, isoleucine and valine decreased significantly. Most of the other amino acids also decreased markedly after the infusion of leucine alone. These results suggest that, in intravenous infusion, leucine plays a specific role on amino acid levels in plasma and muscle of rats.

DDT and immunological responses. 3. Reduced anaphylaxis and mast cell population in rats fed DDT

Previous work showed that anaphylaxis, mast cell population, and tissue histamine content are reduced in guinea pigs given DDT injections. This study was intended to determine whether dietary intake of DDT causes similar effects. Rats immunized with diphtheria toxoid and fed diets containing DDT at 20 and 200 ppm levels for 31 days did not show effects on their serum antitoxin titers, but the numbers of metachromatically stained, histamine-containing mast cells in mesenteries were reduced: in the 20 ppm group by 46% and in the 200 ppm group by 61%. The severity of anaphylactic shock was also reduced in proportion to the DDT dietary levels, and, thus, the magnitude of mast cells. Apparently, daily dietary DDT intake above 2.2 mg DDT/kg of body weight alters the physiology of mast cells in the rat, and thus affects histamine-mediated reactions.

BLOOD SERUM AND TISSUE FREE AMINO ACID CONCENTRATIONS OF GILTS FED DL- OR L-METHIONINE

A semipurified ration containing 0.55% DL-methionine was fed to two gilts from each of two litters, and 0.55% L-methionine was fed to an additional two gilts from each litter. Duodenal, liver, and serum methionine levels were higher when DL-methionine was fed, indicating differences in the abilities of the test gilts to utilize the D- and L-isomers. Serum and muscle methionine levels were higher for litter 2, suggesting possible methionine requirement differences between the two litters. Histidine, isoleucine, and leucine appeared to accumulate in muscle, serum, and liver, respectively, suggesting some form of short-term storage. The accumulation of histidine in muscle tissue was thought to partially explain the fluctuations often associated with serum histidine levels that have not been explainable in terms of diet. A need for further research into factors affecting amino acid requirements was indicated.