Assessment of effects of amino acids and branched chain keto acids on leucine oxidation in human lymphocytes

Productive and physiological implications of top-dress addition of branched-chain amino acids and arginine on lactating sows and offspring

BACKGROUND

Branched-chain amino acids (BCAAs), including L-leucine (L-Leu), L-isoleucine (L-Ile), L-valine (L-Val), and L-arginine (L-Arg), play a crucial role in mammary gland development, secretion of milk and regulation of the catabolic state and immune response of lactating sows. Furthermore, it has recently been suggested that free amino acids (AAs) can also act as microbial modulators. This study aimed at evaluating whether the supplementation of lactating sows with BCAAs (9, 4.5 and 9 g/d/sow of L-Val, L-Ile and L-Leu, respectively) and/or L-Arg (22.5 g/d/sow), above the estimated nutritional requirement, could influence the physiological and immunological parameters, microbial profile, colostrum and milk composition and performance of sows and their offspring.

RESULTS

At d 41, piglets born from the sows supplemented with the AAs were heavier (P = 0.03). The BCAAs increased glucose and prolactin (P < 0.05) in the sows' serum at d 27, tended to increase immunoglobulin A (IgA) and IgM in the colostrum (P = 0.06), increased the IgA (P = 0.004) in the milk at d 20 and tended to increase lymphocyte% in the sows' blood at d 27 (P = 0.07). Furthermore, the BCAAs tended to reduce the Chao1 and Shannon microbial indices (P < 0.10) in the sows' faeces. The BCAA group was discriminated by Prevotellaceae_UCG-004, Erysipelatoclostridiaceae UCG-004, the Rikenellaceae_RC9_gut_group and Treponema berlinense. Arginine reduced piglet mortality pre- (d 7, d 14) and post-weaning (d 41) (P < 0.05). Furthermore, Arg increased the IgM in the sow serum at d 10 (P = 0.05), glucose and prolactin (P < 0.05) in the sow serum at d 27 and the monocyte percentage in the piglet blood at d 27 (P = 0.025) and their jejunal expression of NFKB2 (P = 0.035) while it reduced the expression of GPX-2 (P = 0.024). The faecal microbiota of the sows in Arg group was discriminated by Bacteroidales. The combination of BCAAs and Arg tended to increase spermine at d 27 (P = 0.099), tended to increase the Igs (IgA and IgG, P < 0.10) at d 20 in the milk, favoured the faecal colonisation of Oscillospiraceae UCG-005 and improved piglet growth.

CONCLUSION

Feeding Arg and BCAAs above the estimated requirements for milk production may be a strategy to improve sow productive performance in terms of piglet average daily gain (ADG), immune competence and survivability via modulation of the metabolism, colostrum and milk compositions and intestinal microbiota of the sows. The synergistic effect between these AAs, noticeable by the increase of Igs and spermine in the milk and in the improvement of the performance of the piglets, deserves additional investigation.

Changes in plasma-concentration ratios of branched-chain amino acids in acute and convalescent phases of bacterial pneumonia

Branched-chain amino acids (BCAAs) have different immunity-related functions. Thus, BCAAs require evaluation in terms of their plasma concentration ratio. Eighty healthy participants and 57 patients with community-acquired pneumonia were enrolled. Samples from the healthy participants were collected after 12-h fasting; samples from the community-acquired pneumonia group were collected 2–3 h after lunch, during the acute (day 0) and convalescent (day 7) phases. The coefficient “a” of the regression line (Y = aX + b) of each BCAA plasma concentration was calculated from healthy participants and fixed, and each intercept “b” was calculated from the plasma concentration of each BCAA pair. Isoleucine levels increased; no significant changes in leucine concentrations were observed between healthy participants and pneumonia patients on days 0 and 7. In female participants in the pneumonia group, valine concentrations decreased on day 0. The isoleucine concentration was relatively higher than the leucine concentration on day 7 when evaluated with “b”. Changes in “b” on days 0 and 7 differed between men and women. There were sex-related differences in the plasma concentration ratios of BCAAs evaluated by “b”, which indicates a possible sex-related difference in the metabolic response to bacterial infection.

Metabolic and Physiological Roles of Branched-Chain Amino Acids

Branch chain amino acids (BCAAs) have unique properties with diverse physiological and metabolic roles. They have functions other than simple nutrition. Different diseases including metabolic disease lead to protein loss, especially muscle protein. Supplementation of BCAAs promotes protein synthesis and reduces break down, as well as improving disease conditions. They are important regulators of mTOR signaling pathway and regulate protein synthesis as well as protein turnover. BCAAs facilitate glucose uptake by liver and SK muscle and also enhance glycogen synthesis. Oxidation of BCAAs seems to be beneficial for metabolic health as their catabolism increases fatty acid oxidation and reduces risk of obesity. BCAAs are also important in immunity, brain function, and other physiological aspects of well-being. All three BCAAs are absolutely required for lymphocyte growth and proliferation. They are also important for proper immune cell function. BCAAs may influence brain protein synthesis, and production of energy and may influence synthesis of different neurotransmitters. BCAAs can be used therapeutically and future studies may be directed to investigating the diverse effects of BCAAs in different tissues and their signaling pathways.

Amino acids and immune function

A deficiency of dietary protein or amino acids has long been known to impair immune function and increase the susceptibility of animals and humans to infectious disease. However, only in the past 15 years have the underlying cellular and molecular mechanisms begun to unfold. Protein malnutrition reduces concentrations of most amino acids in plasma. Findings from recent studies indicate an important role for amino acids in immune responses by regulating: (1) the activation of T lymphocytes, B lymphocytes, natural killer cells and macrophages; (2) cellular redox state, gene expression and lymphocyte proliferation; and (3) the production of antibodies, cytokines and other cytotoxic substances. Increasing evidence shows that dietary supplementation of specific amino acids to animals and humans with malnutrition and infectious disease enhances the immune status, thereby reducing morbidity and mortality. Arginine, glutamine and cysteine precursors are the best prototypes. Because of a negative impact of imbalance and antagonism among amino acids on nutrient intake and utilisation, care should be exercised in developing effective strategies of enteral or parenteral provision for maximum health benefits. Such measures should be based on knowledge about the biochemistry and physiology of amino acids, their roles in immune responses, nutritional and pathological states of individuals and expected treatment outcomes. New knowledge about the metabolism of amino acids in leucocytes is critical for the development of effective means to prevent and treat immunodeficient diseases. These nutrients hold great promise in improving health and preventing infectious diseases in animals and humans.

Branched-chain amino acids and immunity

Although there has been great interest in the effects of amino acids on immune function, little is known about the impact of changes in BCAA availability on the ability of the immune system to function. Human immune cells incorporate BCAA into proteins and are able to oxidize BCAA. The immune system exists to protect the host from pathogenic invaders and from other noxious insults. Upon infection, there is a marked increase in demand for substrates by the immune system; these substrates provide energy and are the precursors for the synthesis of new cells, effector molecules, and protective molecules. Cell culture studies show that BCAA are absolutely essential for lymphocytes to synthesize protein, RNA, and DNA and to divide in response to stimulation. In mice, dietary BCAA restriction impairs several aspects of the immune function and increases the susceptibility to pathogens. Postsurgical or septic patients given BCAA intravenously showed improved immunity and this may relate to improved outcome. BCAAs are therefore absolutely essential for lymphocyte responsiveness and are necessary to support other immune cell functions. However, many aspects of BCAA and its effects on immune function have been understudied or not studied at all. More research is needed to understand the extent of the immune system's requirement for BCAA. It is likely that the essentiality of BCAA for the function of immune cells relates to protein synthesis.

Comparison between transport and degradation of leucine and glutamine by peripheral human lymphocytes exposed to concanavalin A

Transport and pathways of leucine and glutamine degradation were evaluated in resting human peripheral lymphocytes and compared with the changes induced by concanavalin A (ConA). Cells were incubated with [1-14C]leucine (0.15 mM), [U-14C]leucine (0.15 mM), or [U-14C]glutamine (0.4 mM) after culture with or without 2, 5, 7, or 10 micrograms/ml ConA for 2, 18, or 24 hours, respectively. Initial rates of transport of leucine and glutamine were augmented 2.7-fold and threefold by the mitogen. Leucine transamination, irreversible oxidation, and catabolism beyond isovaleryl-CoA were increased by 90%, 20%, and 60%, respectively. Glutamine utilization increased threefold; accumulation of glutamate, aspartate, and ammonia increased by 700%, 50%, and 100%, respectively, and 14CO2 production by about 400% in response to ConA. The results indicate that ConA stimulates to about the same extent transport of leucine and glutamine into lymphocytes. Glutamine is mainly channeled into catabolic pathways, while leucine remains largely preserved. It is suggested that these metabolic changes provide more leucine for incorporation into protein and more N- and C-atoms required for the synthesis of macromolecules and energy from glutamine.

Regulation of leucine transport and oxidation in peripheral human lymphocytes by glutamine

In this study we investigated the influence of physiological levels of glutamine, isoleucine, and valine on leucine oxidation and transport by peripheral lymphocytes in an in vitro system. The presence of glutamine in the incubation mixture inhibited leucine oxidation by 61%. This effect was not significantly augmented by addition of isoleucine and valine. Leucine transport revealed a Km of 124 mumol/L and a Vmax of 24 pmol/10(6) cells/30 sec. Glutamine inhibited leucine transport by 63%. The capacity of lymphocytes for leucine transport exceeded the capacity for leucine oxidation by a factor of 7.8 (13.6 +/- 0.6 v 1.74 +/- 0.1 pmol/10(6) cells/30 sec). It is concluded that glutamine is a regulator of leucine transport and oxidation in human peripheral lymphocytes, and the inhibition of leucine oxidation by glutamine is not due to an alteration of leucine transport but reflects an intracellular event.