Effect of enteral glutamine or glycine on whole-body nitrogen kinetics in very-low-birth-weight infants

Glutamine supplementation moderately affects growth, plasma metabolite and free amino acid patterns in neonatal low birth weight piglets

Low birth weight (LBW) neonates show impaired growth compared with normal birth weight (NBW) neonates. Glutamine (Gln) supplementation benefits growth of weaning piglets, while the effect on neonates is not sufficiently clear. We examined the effect of neonatal Gln supplementation on piglet growth, milk intake and metabolic parameters. Sow-reared pairs of newborn LBW (0·8-1·2 kg) and NBW (1·4-1·8 kg) male piglets received Gln (1 g/kg body mass (BM)/d; Gln-LBW, Gln-NBW; n 24/group) or isonitrogenous alanine (1·22 g/kg BM/d; Ala-LBW; Ala-NBW; n 24/group) supplementation at 1-5 or 1-12 d of age (daily in three equal portions at 07:00, 12:00 and 17:00 by syringe feeding). We measured piglet BM, milk intake (1, 11-12 d), plasma metabolite, insulin, amino acid (AA) and liver TAG concentrations (5, 12 d). The Gln-LBW group had higher BM (+7·5%, 10 d, P = 0·066; 11-12 d, P < 0·05) and milk intake (+14·7%, P = 0·015) than Ala-LBW. At 5 d, Ala-LBW group had higher plasma TAG (+34·7%, P < 0·1) and lower carnosine (-22·5%, P < 0·05) than Ala-NBW and Gln-LBW, and higher liver TAG (+66·9%, P = 0·029) than Ala-NBW. At 12 d, plasma urea was higher (+37·5%, P < 0·05) with Gln than Ala supplementation. Several proteinogenic AA in plasma were lower (P < 0·05) in Ala-NBW v. Gln-NBW. Plasma arginine was higher (P < 0·05) in Gln-NBW v Ala-NBW piglets (5, 12 d). Supplemental Gln moderately improved growth and milk intake and affected lipid metabolism in LBW piglets and AA metabolism in NBW piglets, suggesting effects on intestinal and liver function.

Effects of Weight Loss and Moderate-Protein, High-Fiber Diet Consumption on the Fasted Serum Metabolome of Cats

Feline obesity elicits a plethora of metabolic responses leading to comorbidities, with potential reversal during weight loss. The specific metabolic alterations and biomarkers of organ dysfunction are not entirely understood. Untargeted, high-throughput metabolomic technologies may allow the identification of biological components that change with weight status in cats, increasing our understanding of feline metabolism. The objective of this study was to utilize untargeted metabolomic techniques to identify biomarkers and gain mechanistic insight into the serum metabolite changes associated with reduced food intake and weight loss in overweight cats. During a four-wk baseline period, cats were fed to maintain body weight. For 18 wk following baseline, cats were fed to lose weight at a rate of ~1.5% body weight/wk. Blood serum metabolites were measured at wk 0, 1, 2, 4, 8, 12, and 16. A total of 535 named metabolites were identified, with up to 269 of them being altered (p- and q-values < 0.05) at any time point. A principal component analysis showed a continual shift in metabolite profile as weight loss progressed, with early changes being distinct from those over the long term. The majority of lipid metabolites decreased with weight loss; however, ketone bodies and small lipid particles increased with weight loss. The majority of carbohydrate metabolites decreased with weight loss. Protein metabolites had a variable result, with some increasing, but others decreasing with weight loss. Metabolic mediators of inflammation, oxidative stress, xenobiotics, and insulin resistance decreased with weight loss. In conclusion, global metabolomics identified biomarkers of reduced food intake and weight loss in cats, including decreased markers of inflammation and/or altered macronutrient metabolism.

Glutamine supplementation for young infants with severe gastrointestinal disease

BACKGROUND

Endogenous glutamine biosynthesis may be insufficient to meet the needs of people with severe gastrointestinal disease. Results from studies using experimental animal models of gastrointestinal disease have suggested that glutamine supplementation improves clinical outcomes. This review examines evidence on the effect of glutamine supplementation in young infants with severe gastrointestinal disease.

OBJECTIVES

To assess the effect of supplemental glutamine on mortality and morbidity in young infants with severe gastrointestinal disease.

SEARCH METHODS

We searcheed the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2014, Issue 8), MEDLINE, EMBASE, and CINAHL (from inception to September 2014), conference proceedings, and reference lists from previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in infants up to three months old (corrected for preterm birth if necessary) with severe gastrointestinal disease defined as a congenital or acquired gastrointestinal condition that is likely to necessitate providing parenteral nutrition for at least 24 hours.

DATA COLLECTION AND ANALYSIS

Two review authors assessed trial eligibility and risk of bias and undertook data extraction independently. We analysed the treatment effects in the individual trials and reported the risk ratio (RR) and risk difference (RD) for dichotomous data and mean difference for continuous data, with 95% confidence intervals (CI). We used a fixed-effect model in meta-analyses and explored the potential causes of heterogeneity in sensitivity analyses.

MAIN RESULTS

We found three trials in which a total of 274 infants participated. The trials were of good methodological quality but were too small to detect clinically important effects of glutamine supplementation. Meta-analyses did not reveal a statistically significant difference in the risk of death before hospital discharge (typical RR 0.79, 95% CI 0.19 to 3.20; typical RD -0.01, 95% CI -0.05 to 0.03) or in the rate of invasive infection (typical RR 1.37, 95% CI 0.89 to 2.11; typical RD 0.08, 95% CI -0.03 to 0.18]).

AUTHORS' CONCLUSIONS

The available data from randomised controlled trials do not suggest that glutamine supplementation has any important benefits for young infants with severe gastrointestinal disease.

Maternal glucocorticoid elevation and associated blood metabonome changes might be involved in metabolic programming of intrauterine growth retardation in rats exposed to caffeine prenatally

Our previous studies demonstrated that prenatal caffeine exposure causes intrauterine growth retardation (IUGR), fetuses are over-exposed to high levels of maternal glucocorticoids (GC), and intrauterine metabolic programming and associated metabonome alteration that may be GC-mediated. However, whether maternal metabonomes would be altered and relevant metabolite variations might mediate the development of IUGR remained unknown. In the present studies, we examined the dose- and time-effects of caffeine on maternal metabonome, and tried to clarify the potential roles of maternal GCs and metabonome changes in the metabolic programming of caffeine-induced IUGR. Pregnant rats were treated with caffeine (0, 20, 60 or 180 mg/kg·d) from gestational days (GD) 11 to 20, or 180 mg/kg·d caffeine from GD9. Metabonomes of maternal plasma on GD20 in the dose-effect study and on GD11, 14 and 17 in the time-course study were analyzed by ¹H nuclear magnetic resonance spectroscopy, respectively. Caffeine administration reduced maternal weight gains and elevated both maternal and fetal corticosterone (CORT) levels. A negative correlation between maternal/fetal CORT levels and fetal bodyweight was observed. The maternal metabonome alterations included attenuated metabolism of carbohydrates, enhanced lipolysis and protein breakdown, and amino acid accumulation, suggesting GC-associated metabolic effects. GC-associated metabolite variations (α/β-glucoses, high density lipoprotein-cholesterol, β-hydroxybutyrate) were observed early following caffeine administration. In conclusion, prenatal caffeine exposure induced maternal GC elevation and metabonome alteration, and maternal GC and relevant discriminatory metabolites might be involved in the metabolic programming of caffeine-induced IUGR.

Glutamine randomized studies in early life: the unsolved riddle of experimental and clinical studies

Glutamine may have benefits during immaturity or critical illness in early life but its effects on outcome end hardpoints are controversial. Our aim was to review randomized studies on glutamine supplementation in pups, infants, and children examining whether glutamine affects outcome. Experimental work has proposed various mechanisms of glutamine action but none of the randomized studies in early life showed any effect on mortality and only a few showed some effect on inflammatory response, organ function, and a trend for infection control. Although apparently safe in animal models (pups), premature infants, and critically ill children, glutamine supplementation does not reduce mortality or late onset sepsis, and its routine use cannot be recommended in these sensitive populations. Large prospectively stratified trials are needed to better define the crucial interrelations of “glutamine-heat shock proteins-stress response” in critical illness and to identify the specific subgroups of premature neonates and critically ill infants or children who may have a greater need for glutamine and who may eventually benefit from its supplementation. The methodological problems noted in the reviewed randomized experimental and clinical trials should be seriously considered in any future well-designed large blinded randomized controlled trial involving glutamine supplementation in critical illness.

Glutamine supplementation for young infants with severe gastrointestinal disease

BACKGROUND

Endogenous glutamine biosynthesis may be insufficient to meet the needs of people with severe gastrointestinal disease. Studies using experimental animal models and controlled trials in adult patients with severe gastrointestinal disease have suggested that glutamine supplementation improves clinical outcomes. This review examines evidence for the effect of glutamine supplementation in young infants with severe gastrointestinal disease.

OBJECTIVES

To assess the evidence from randomised controlled trials that providing supplemental glutamine reduces mortality and morbidity in young infants with severe gastrointestinal disease.

SEARCH METHODS

We used the standard search strategy of the Cochrane Neonatal Review Group. This included searches of the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2012, Issue 1), MEDLINE, EMBASE, and CINAHL (to November 2011), conference proceedings, and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in infants up to three months old (corrected for preterm birth if necessary) with severe gastrointestinal disease defined as a congenital or acquired gastrointestinal condition that is likely to necessitate providing parenteral nutrition for at least 24 hours.

DATA COLLECTION AND ANALYSIS

We extracted data using the standard methods of the Cochrane Neonatal Review Group with separate evaluation of trial quality and data extraction by two review authors. We synthesised data using a fixed-effect model and reported typical risk ratio (RR), typical risk difference (RD), and weighted mean difference (WMD).

MAIN RESULTS

We found two trials in which a total of 100 infants participated. The trials were of good methodological quality but were too small to detect clinically important effects of glutamine supplementation. Meta-analysis did not reveal a statistically significant difference in the risk of death before hospital discharge (typical RR 1.57; 95% confidence interval (95% CI) 0.25 to 9.66; RD 0.02; 95% CI -0.06 to 0.10) or in the rate of invasive infection [typical RR 1.22; 95% CI 0.55 to 2.70; RD 0.04; 95% CI -0.12 to 0.20).

AUTHORS' CONCLUSIONS

The available data from randomised controlled trials are insufficient to determine whether glutamine supplementation has any important benefits for young infants with severe gastrointestinal disease.

Investigating potential mechanisms of obesity by metabolomics

Obesity is a serious health problem with an increased risk of several common diseases including diabetes, cardiovascular disease, and cancer. Metabolomics is an emerging analytical technique for systemic determination of metabolite profiles, which is useful for understanding the biochemical changes in obesity or related diseases both in individual organs and at the organism level. Increasingly, this technology has been applied to the study of obesity, complementing transcriptomics and/or proteomics analyses. Indeed, the alterations of metabolites in biofluids/tissues are direct indicators of variations in physiology or pathology. In this paper, we will examine the obesity-related alterations in significant metabolites that have been identified by metabolomics as well as their metabolic pathway associations. Issues concerning the screening of biologically significant metabolites related to obesity will also be discussed.

1H-NMR-based metabolic profiling of maternal and umbilical cord blood indicates altered materno-foetal nutrient exchange in preterm infants

Background

Adequate foetal growth is primarily determined by nutrient availability, which is dependent on placental nutrient transport and foetal metabolism. We have used ¹H nuclear magnetic resonance (NMR) spectroscopy to probe the metabolic adaptations associated with premature birth.

Methodology

The metabolic profile in ¹H NMR spectra of plasma taken immediately after birth from umbilical vein, umbilical artery and maternal blood were recorded for mothers delivering very-low-birth-weight (VLBW) or normo-ponderal full-term (FT) neonates.

Principal Findings

Clear distinctions between maternal and cord plasma of all samples were observed by principal component analysis (PCA). Levels of amino acids, glucose, and albumin-lysyl in cord plasma exceeded those in maternal plasma, whereas lipoproteins (notably low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) and lipid levels were lower in cord plasma from both VLBW and FT neonates. The metabolic signature of mothers delivering VLBW infants included decreased levels of acetate and increased levels of lipids, pyruvate, glutamine, valine and threonine. Decreased levels of lipoproteins glucose, pyruvate and albumin-lysyl and increased levels of glutamine were characteristic of cord blood (both arterial and venous) from VLBW infants, along with a decrease in levels of several amino acids in arterial cord blood.

Conclusion

These results show that, because of its characteristics and simple non-invasive mode of collection, cord plasma is particularly suited for metabolomic analysis even in VLBW infants and provides new insights into the materno-foetal nutrient exchange in preterm infants.

Amino acid metabolism in the human fetus at term: leucine, valine, and methionine kinetics

Human fetal metabolism is largely unexplored. Understanding how a healthy fetus achieves its fast growth rates could eventually play a pivotal role in improving future nutritional strategies for premature infants. To quantify specific fetal amino acid kinetics, eight healthy pregnant women received before elective cesarean section at term, continuous stable isotope infusions of the essential amino acids [1-13C,15N]leucine, [U-13C5]valine, and [1-13C]methionine. Umbilical blood was collected after birth and analyzed for enrichments and concentrations using mass spectrometry techniques. Fetuses showed considerable leucine, valine, and methionine uptake and high turnover rates. α-Ketoisocaproate, but not α-ketoisovalerate (the leucine and valine ketoacids, respectively), was transported at net rate from the fetus to the placenta. Especially, leucine and valine data suggested high oxidation rates, up to half of net uptake. This was supported by relatively low α-ketoisocaproate reamination rates to leucine. Our data suggest high protein breakdown and synthesis rates, comparable with, or even slightly higher than in premature infants. The relatively large uptakes of total leucine and valine carbon also suggest high fetal oxidation rates of these essential branched chain amino acids.

Glutamine supplementation in sick children: is it beneficial?

The purpose of this review is to provide a critical appraisal of the literature on Glutamine (Gln) supplementation in various conditions or illnesses that affect children, from neonates to adolescents. First, a general overview of the proposed mechanisms for the beneficial effects of Gln is provided, and subsequently clinical studies are discussed. Despite safety, studies are conflicting, partly due to different effects of enteral and parenteral Gln supplementation. Further insufficient evidence is available on the benefits of Gln supplementation in pediatric patients. This includes premature infants, infants with gastrointestinal disease, children with Crohn's disease, short bowel syndrome, malnutrition/diarrhea, cancer, severe burns/trauma, Duchenne muscular dystrophy, sickle cell anemia, cystic fibrosis, and type 1 diabetes. Moreover, methodological issues have been noted in some studies. Further mechanistic data is needed along with large randomized controlled trials in select populations of sick children, who may eventually benefit from supplemental Gln.

Methionine and protein metabolism in non-alcoholic steatohepatitis: evidence for lower rate of transmethylation of methionine

Hepatic metabolism of methionine is the source of cysteine, the precursor of glutathione, the major intracellular antioxidant in the body. Methionine also is the immediate precursor of SAM (S-adenosylmethionine) the key methyl donor for phosphatidylcholine synthesis required for the export of VLDL (very-low-density lipoprotein) triacylglycerols (triglycerides) from the liver. We have examined the kinetics of methionine, its transmethylation and trans-sulfuration with estimates of whole body rate of protein turnover and urea synthesis in clinically stable biopsy-confirmed subjects with NASH (non-alcoholic steatohepatitis). Subjects with NASH were more insulin-resistant and had significantly higher plasma concentrations of usCRP (ultrasensitive C-reactive protein), TNFα (tumour necrosis factor α) and other inflammatory cytokines. There was no significant effect of insulin resistance and NASH on whole body rate of protein turnover [phenylalanine Ra (rate of appearance)] and on the rate of urea synthesis. The rates of methylation of homocysteine and transmethylation of methionine were significantly lower in NASH compared with controls. There was no difference in the rate of trans-sulfuration of methionine between the two groups. Enteric mixed nutrient load resulted in a significant increase in all the measured parameters of methionine kinetics. Heterozygosity for MTHFR (5,10-methylene-tetrahydrofolate reductase) (677C→T) did not have an impact on methionine metabolism. We speculate that, as a result of oxidant stress possibly due to high fatty acid oxidation, the activity of methionine adenosyltransferase is attenuated resulting in a lower rate of transmethylation of methionine and of SAM synthesis. These results are the first evidence for perturbed metabolism of methionine in NASH in humans and provide a rationale for the development of targeted intervention strategies.

Majority of dietary glutamine is utilized in first pass in preterm infants

Glutamine is a conditionally essential amino acid for very low-birth weight infants by virtue of its ability to play an important role in several key metabolic processes of immune cells and enterocytes. Although glutamine is known to be used to a great extent, the exact splanchnic metabolism in enterally fed preterm infants is unknown. We hypothesized that preterm infants show a high splanchnic first-pass glutamine metabolism and the primary metabolic fate of glutamine is oxidation. Five preterm infants (mean + or - SD birth weight 1.07 + or - 0.22 kg and GA 29 + or - 2 wk) were studied by dual tracer ([U-(13)C]glutamine and [(15)N(2)]glutamine) cross-over techniques on two study days (at postnatal week 3 + or - 1 wk). Splanchnic and whole-body glutamine kinetics were assessed by plasma isotopic enrichment of [U-(13)C]glutamine and [(15)N(2)]glutamine and breath (13)CO(2) enrichments. Mean fractional first-pass glutamine uptake was 73 + or - 6% and 57 + or - 17% on the study days. The splanchnic tissues contributed for a large part (57 + or - 6%) to the total amount of labeled carbon from glutamine retrieved in expiratory air. Dietary glutamine is used to a great extent by the splanchnic tissues in preterm infants and its carbon skeleton has an important role as fuel source.

Cytokine responses in very low birth weight infants receiving glutamine-enriched enteral nutrition

OBJECTIVE

Very low birth weight (VLBW) infants receiving glutamine-enriched enteral nutrition may present with a lower infection rate, which may result from enhanced antimicrobial innate or Th1 cytokine responses. We investigated whether glutamine-enriched enteral nutrition in VLBW infants increased these cytokine responses following in vitro stimulation of whole blood cells.

METHODS

In a double-blind, placebo-controlled, randomized controlled trial, VLBW infants (gestational age <32 weeks and/or birth weight <1500 g) received enteral glutamine supplementation (0.3 g x kg(-1) x day(-1)) or isonitrogenous placebo supplementation (alanine) between days 3 and 30 of life. Cytokine responses following in vitro whole blood cell stimulation with anti-(alpha)CD3/alphaCD28 or lipopolysaccharide were analyzed by cytometric bead array at 3 time points: before the start of the study, at day 7 of life, and at day 14 of life.

RESULTS

Baseline patient and nutritional characteristics were not different between groups. At least 2 blood samples were analyzed in 25 of 52 (48%) and 38 of 50 (76%) infants in the glutamine-supplemented and control groups, respectively. Glutamine-enriched enteral nutrition was not associated with significant alterations in cytokine responses (interferon-gamma, tumor necrosis factor-alpha, interleukin [IL]-2, IL-4, IL-5, and IL-10) of peripheral blood cells upon stimulation with either anti-alphaCD3/alphaCD28 or lipopolysaccharide.

CONCLUSIONS

We hypothesize that glutamine-enriched enteral nutrition decreases the infection rate in VLBW infants by influencing the mucosal and not the systemic immune system.

Protein and amino acid metabolism in the human newborn

Birth and adaptation to extrauterine life involve major shifts in the protein and energy metabolism of the human newborn. These include a shift from a state of continuous supply of nutrients including amino acids from the mother to cyclic periodic oral intake, a change in the redox state of organs, thermogenesis, and a significant change in the mobilization and use of oxidative substrates. The development of safe, stable isotopic tracer methods has allowed the study of protein and amino acid metabolism not only in the healthy newborn but also in those born prematurely and of low birth weight. These studies have identified the unique and quantitative aspects of amino acid/protein metabolism in the neonate, thus contributing to rational nutritional care of these babies. The present review summarizes the contemporary data on some of the significant developments in essential and dispensable amino acids and their relationship to overall protein metabolism. Specifically, the recent data of kinetics of leucine, phenylalanine, glutamine, sulfur amino acid, and threonine and their relation to whole-body protein turnover are presented. Finally, the physiological rationale and the impact of nutrient (amino acids) interventions on the dynamics of protein metabolism are discussed.

Comparative aspects of tissue glutamine and proline metabolism

The cellular metabolism of glutamine and proline are closely interrelated, because they can be interconverted with glutamate and ornithine via the mitochondrial pathway involving pyrroline-5-carboxylate (P5C). In adults, glutamine and proline are converted via P5C to citrulline in the gut, then citrulline is converted to arginine in the kidney. In neonates, arginine is a semiindispensable amino acid and is synthesized from proline completely in the gut; because of low P5C synthase activity, glutamine is not an important precursor for neonatal arginine synthesis. Thus, splanchnic metabolism of glutamine and proline is important, because both amino acids serve as key precursors for arginine synthesis with some developmental differences. Studies investigating splanchnic extraction demonstrate that about two-thirds of dietary glutamine and almost all dietary glutamate are extracted on first pass and the vast majority is oxidized in the gut. This capacity to extract glutamine and glutamate appears to be very large, so diets high in glutamine or glutamate probably have little impact on circulating concentrations and consequent potential toxicity. In contrast, it appears that very little proline is extracted by the gut and liver, at least in the neonate, which may result in hyperprolinemia and potential toxicity. Therefore, the upper limits of safe dietary intake for glutamine and proline, and other amino acids, appear to be substantially different depending on the extent of first-pass splanchnic extraction and irreversible catabolism.

Glutamine supplementation in the newborn infant

Glutamine is a non-essential amino acid that can be synthesized de novo from glutamate. This synthesis can be increased by intravenous infusion of carbon precursors (alpha-ketoglutarate or amino acids) in adults and in infants. The metabolism of glutamine is highly compartmentalized between the splanchnic tissues and the periphery, so that orally administered glutamine is completely metabolized in the splanchnic compartment. Data from studies in adults and children show that plasma levels of glutamine decline during acute stress and illness. Because of its importance in several physiological functions (the demonstrated benefits of supplemental glutamine in adult burns and trauma patients and the inhibitory effect on proteolysis in the skeletal muscle in vitro), it has been suggested that during 'acute stress' the demands of glutamine outweigh its de novo synthesis, resulting in a fall in plasma glutamine levels. As a consequence, glutamine has been considered a 'conditionally essential' amino acid. Because of its instability in solution, glutamine is not routinely added to the parenteral amino acid mixtures. A number of clinical trials of parenteral and enteral supplementation of glutamine have been performed. The outcome measures examined have varied between acute effects and long-term complex clinical events such as mortality and risk of infections. Although acute studies in LBW babies have shown some beneficial effects such as changes in protein metabolism and activation of immune system, these have not been translated into prolonged advantages such as reduction in mortality or in nosocomial infection. The reasons for these differences are discussed.

Glutamine supplementation for young infants with severe gastrointestinal disease

BACKGROUND

Endogenous glutamine biosynthesis may be insufficient to meet the needs of infants with severe gastrointestinal disease. Studies using animal models of gastrointestinal disease and controlled trials in adult patients have suggested that glutamine supplementation improves clinical outcomes.

OBJECTIVES

To assess the evidence from randomised controlled trials that providing supplemental glutamine reduces mortality and morbidity in infants with severe gastrointestinal disease.

SEARCH STRATEGY

The standard search strategy of the Cochrane Neonatal Review Group was used. This included searches of the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2006), MEDLINE (1966 - August 2006), EMBASE (1980 - August 2006), conference proceedings, and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in infants (up to three months old, corrected for preterm birth) with severe gastrointestinal disease (defined as a congenital or acquired gastrointestinal condition that is likely to necessitate providing parenteral nutrition for at least 24 hours).

DATA COLLECTION AND ANALYSIS

Data were extracted using the standard methods of the Cochrane Neonatal Review Group, with separate evaluation of trial quality and data extraction by two reviewer authors, and synthesis of data using relative risk, risk difference and weighted mean difference.

MAIN RESULTS

Two trials in which a total of 100 infants participated were identified. In one trial, a minority of participants were infants older than three months. These studies were generally of good methodological quality but were underpowered to detect clinically important effects of glutamine supplementation. Meta-analysis did not reveal a statistically significant difference in the risk of death before hospital discharge [typical relative risk 1.57 (95% confidence interval 0.25 to 9.66); typical risk difference 0.02 (95% confidence interval -0.06 to 0.10)], nor in the rate of invasive infection [typical relative risk 1.22 (95% confidence interval 0.55 to 2.70); typical risk difference: 0.04 (95% confidence interval -0.12 to 0.20)].

AUTHORS' CONCLUSIONS

The available data from randomised controlled trials are not sufficient to determine whether glutamine supplementation confers clinically significant benefits for infants with severe gastrointestinal disease. Further trials are needed.

Oral glutamine and amino acid supplementation inhibit whole-body protein degradation in children with Duchenne muscular dystrophy

BACKGROUND

Glutamine has been shown to acutely decrease whole-body protein degradation in Duchenne muscular dystrophy (DMD).

OBJECTIVE

To improve nutritional support in DMD, we tested whether oral supplementation with glutamine for 10 d decreased whole-body protein degradation significantly more than did an isonitrogenous amino acid control mixture.

DESIGN

Twenty-six boys with DMD were included in this randomized, double-blind parallel study; they received an oral supplement of either glutamine (0.5 g . kg(-1) . d(-1)) or an isonitrogenous, nonspecific amino acid mixture (0.8 g . kg(-1) . d(-1)) for 10 d. The subjects in each group were not clinically different at entry. Leucine and glutamine metabolisms were estimated in the postabsorptive state by using a primed continuous intravenous infusion of [1-(13)C]leucine and [2-(15)N]glutamine before and 10 d after supplementation.

RESULTS

A significant effect of time was observed on estimates of whole-body protein degradation. A significant (P < 0.05) decrease in the rate of leucine appearance (an index of whole-body protein degradation) was observed after both glutamine and isonitrogenous amino acid supplementation [x +/-SEM: 136 +/- 9 to 124 +/- 6 micromol . kg fat-free mass (FFM)(-1) . h(-1) for glutamine and 136 +/- 6 to 131 +/- 8 micromol . kg FFM(-1) . h(-1) for amino acids]. A significant (P < 0.05) decrease in endogenous glutamine due to protein breakdown was also observed (91 +/- 6 to 83 +/- 4 micromol . kg FFM(-1) . h(-1) for glutamine and 91 +/- 4 to 88 +/- 5 micromol . kg FFM(-1) . h(-1) for amino acids). The decrease in the estimates of whole-body protein degradation did not differ significantly between the 2 supplemental groups.

CONCLUSION

Oral glutamine or amino acid supplementation over 10 d equally inhibits whole-body protein degradation in DMD.

Effect of intravenous amino acids on glutamine and protein kinetics in low-birth-weight preterm infants during the immediate neonatal period

Glutamine may be a conditionally essential amino acid in low-birth-weight (LBW) preterm neonates. Exogenously administered amino acids, by providing anaplerotic carbon into the tricarboxylic acid cycle, could result in greater cataplerotic efflux and glutamine de novo synthesis. The effect of dose and duration of amino acid infusion on glutamine and nitrogen (N) kinetics was examined in LBW infants in the period immediately after birth. Preterm neonates (<32 weeks gestation, birth weights 809-1,755 g) were randomized to initially receive either 480 or 960 micromol x kg(-1) x h(-1) of an intravenous amino acid solution for 19-24 hours, followed by a higher or lower amino acid load for either 5 h or 24 h. Glutamine de novo synthesis, leucine N, phenylalanine, and urea kinetics were determined using stable isotopic tracers. An increase in amino acid infusion from 480 to 960 micromol x kg(-1) x h(-1) for 5 h resulted in decreased glutamine de novo synthesis in every neonate (384.4 +/- 38.0 to 368.9 +/- 38.2 micromol x kg(-1) x h(-1), P < 0.01) and a lower whole body rate of proteolysis (P < 0.001) and urea synthesis (P < 0.001). However, when the increased amino acid infusion was extended for 24 h, glutamine de novo synthesis increased (369.7 +/- 92.6 to 483.4 +/- 97.5 micromol x kg(-1) x h(-1), P < 0.001), whole body rate of proteolysis did not change, and urea production increased. Decreasing the amino acid load resulted in a decrease in glutamine rate of appearance (R(a)) and leucine N R(a), but had no effect on phenylalanine R(a). Acutely stressed LBW infants responded to an increase in amino acid load by transiently suppressing whole body rate of glutamine synthesis, proteolysis, and oxidation of protein. The mechanisms of this transient effect on whole body protein/nitrogen metabolism remain unknown.

Transamination of leucine and nitrogen accretion in human pregnancy and the newborn infant

Kinetics of leucine and its oxidation were determined in human pregnancy and in the newborn infant, using stable isotopic tracers, to quantify the dynamic aspects of protein metabolism. These data show that in human pregnancy there is a decrease in whole-body rate of leucine turnover compared with nonpregnant women. In addition, data in newborn infants show that leucine turnover expressed as per kg body weight is higher compared with adults. The administering of nutrients resulted in a suppression of the whole-body rate of proteolysis. Because nonessential amino nitrogen is an important component of nutritional nitrogen and can be limiting for growth under certain circumstances, and because BCAA are an important source of nonessential amino nitrogen, we have examined the relations among the transamination of leucine, leucine N kinetics, and urea synthesis and glutamine kinetics in human pregnancy and newborn infants. In human pregnancy, early in gestation, there is a significant decrease in urea synthesis in association with a decrease in the rate of transamination of leucine. A linear correlation was evident between the rate of leucine reamination and urea synthesis during fasting in pregnant and nonpregnant women. In healthy-term newborn and growing infants, although the reamination of leucine was positively related to glutamine flux, leucine reamination was negatively related to urea synthesis, suggesting a redirection of amino N toward protein accretion. The regulatory mechanism involved in this redirection of nitrogen from irreversible loss to accretion remains under investigation.

Amino acids, glutamine, and protein metabolism in very low birth weight infants

Glutamine has been proposed to be conditionally essential for premature infants, and the currently used parenteral nutrient mixtures do not contain glutamine. De novo glutamine synthesis (DGln) is linked to inflow of carbon into and out of the tricarboxylic acid (TCA) cycle. We hypothesized that a higher supply of parenteral amino acids by increasing the influx of amino acid carbon into the TCA cycle will enhance the rate of DGln. Very low birth weight infants were randomized to receive parenteral amino acids either 1.5 g/kg/d for 20 h followed by 3.0 g/kg/d for 5 h (AA1.5) or 3.0 g/kg/d for 20 h followed by 1.5 g/kg/d for 5 h (AA3.0). A third group of babies received amino acids 1.5 g/kg/d for 20 h followed by 3.0 g/kg/d for 20 h (AA-Ext). Glutamine and protein/nitrogen kinetics were examined using [5-(15)N]glutamine, [2H5]phenylalanine, [1-(13)C,15N]leucine, and [15N2]urea tracers. An acute increase in parenteral amino acid infusion for 5 h (AA1.5) resulted in decrease in rate of appearance (Ra) of phenylalanine and urea, but had no effect on glutamine Ra. Infusion of amino acids at 3.0 g/kg/d for 20 h resulted in increase in DGln, leucine transamination, and urea synthesis, but had no effect on Ra phenylalanine (AA-Ext). These data show an acute increase in parenteral amino acid-suppressed proteolysis, however, such an effect was not seen when amino acids were infused for 20 h and resulted in an increase in glutamine synthesis.

A randomized controlled trial of enteral glutamine supplementation in very low birth weight infants: plasma amino acid concentrations

OBJECTIVE

Glutamine depletion has negative effects on the functional integrity of the gut and leads to immunosuppression. Very low birth weight (VLBW) infants are susceptible to glutamine depletion, as enteral nutrition is limited in the first weeks of life. Enteral glutamine supplementation may have a positive effect on feeding tolerance, infectious morbidity and short-term outcome. The aim of the study was to determine the effect of enteral glutamine supplementation on plasma amino acid concentrations, reflecting one aspect of safety of enteral glutamine supplementation in VLBW infants.

METHODS

In a double-blind placebo-controlled randomized controlled trial, VLBW infants (gestational age <32 weeks or birth weight <1500 g) received enteral glutamine supplementation (0.3 g/kg per day) or isonitrogenous placebo supplementation (alanine) between day 3 and day 30 of life. Supplementation was added to breast milk or to preterm formula. Plasma amino acid concentrations were measured at four time points: before the start of the study and at days 7, 14 and 30 of life.

RESULTS

Baseline patient and nutritional characteristics were not different in glutamine (n = 52) and control (n = 50) groups. Plasma concentrations of most essential and non-essential amino acids increased throughout the study period. There was no effect of enteral glutamine supplementation. In particular, the increase of plasma glutamine and glutamate concentrations was not different between the treatment groups (P = 0.49 and P = 0.34 respectively, day 30).

CONCLUSIONS

Enteral glutamine supplementation in VLBW infants does not alter plasma concentrations of glutamine, glutamate or other amino acids. Enteral supplementation in a dose of 0.3 g/kg per day seems safe in VLBW infants.

Glutamine-enriched enteral nutrition in very-low-birth-weight infants and effects on feeding tolerance and infectious morbidity: a randomized controlled trial

BACKGROUND

Glutamine depletion has negative effects on the functional integrity of the gut and leads to immunosuppression. Very-low-birth-weight (VLBW) infants are susceptible to glutamine depletion because nutrition is limited in the first weeks of life.

OBJECTIVE

The objective was to determine the effect of glutamine-enriched enteral nutrition on feeding tolerance, infectious morbidity, and short-term outcome in VLBW infants.

DESIGN

In a double-blind randomized controlled trial, VLBW infants (gestational age <32 wk or birth weight <1500 g) were allocated to receive enteral glutamine supplementation (0.3 g . kg(-1) . d(-1)) or isonitrogenous control supplementation (alanine) between days 3 and 30 of life. The supplementations were added to breast milk or to preterm formula. The primary endpoint for the study was time to full enteral feeding. Secondary endpoints were other variables of feeding tolerance, infectious morbidity, and short-term outcome.

RESULTS

Baseline patient and nutritional characteristics were not significantly different in the glutamine-supplemented (n = 52) and the control (n = 50) groups. The median time to full enteral feeding was 13 d (range: 7-31 d) in the glutamine-supplemented group and 13 d (range: 6-35 d) in the control group (hazard ratio: 1.19; 95% CI: 0.79, 1.79; P = 0.40). In the glutamine-supplemented group, 26 of 52 infants (50%) had >/=1 serious infection compared with 38 of 50 (76%) in the control group (odds ratio: 0.32; 95% CI: 0.14, 0.74; P = 0.008). Other variables of feeding tolerance and short-term outcome were not significantly different between groups.

CONCLUSIONS

Glutamine-enriched enteral nutrition did not improve feeding tolerance or short-term outcome in VLBW infants. However, infectious morbidity was significantly lowered in infants who received glutamine-enriched enteral nutrition.

Feeding strategies and necrotizing enterocolitis

PURPOSE OF REVIEW

To update clinical trials concerning feeding strategies or feeding interventions to prevent necrotizing enterocolitis (NEC).

RECENT FINDINGS

The overall incidence of NEC remains unchanged. Several studies have shown that it is safe to use small feeding volumes early in life even in selected circumstances, such as feeding during the use of indomethacin to treat symptomatic patent ductus arteriosus. Although descriptive case reports have linked some feeding interventions such as thickened feedings to NEC, there is no evidence to establish a causal relation. Interestingly, one report showed that neither the presence of-nor characteristics of-gastric residuals was helpful to identify those infants who subsequently develop NEC. Numerous studies in animals show that vascular and host defense responses are not adequate in the immature gut. A few small clinical trials showed that various feeding strategies may alter these responses in preterm infants. However, larger clinical trials around these issues await further characterization of the mechanisms that regulate these two aspects of gastrointestinal function with respect to feeding.

SUMMARY

Studies continue to demonstrate how fragile the immature gut is, but further work directed to understanding the mechanisms that regulate gastrointestinal responses to feeding is needed to design meaningful interventions for large prospective trials.

The use of oral rehydration solutions in children and adults

The observation that the intestinal Na(+)-glucose cotransporter remains intact in most diarrheal illnesses led to development of the life-saving, low-cost technology of oral rehydration salt (ORS) solutions. The primary therapeutic role of ORS solutions is in prevention and treatment of dehydration during management of acute gastroenteritis. Successful oral rehydration therapy involves early use of ORS with maintenance or timely resumption of regular feeding. Since the inception of the oral rehydration approach more than three decades ago, the widespread use of ORS solutions has revolutionized the management and outcomes of acute gastroenteritis in children and adults. The efficacy of the World Health Organization ORS solution and of commercial ORS formulations has been enhanced by reducing osmolarity. Newer formulations of ORS are under active investigation, with promise of added benefits, including promotion of intestinal healing. This article reviews fluid and electrolyte transport in the gastrointestinal tract, the pathophysiologic mechanisms of acute diarrhea, and the basis and formulation of current and newer ORS solutions. Guidelines for efficacious use of ORS in the management of acute gastroenteritis and short gut syndrome are also provided.