The effect of glutamine-enriched enteral nutrition on intestinal permeability in very-low-birth-weight infants: a randomized controlled trial

Impact of neonatal nutrition on necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of morbidity and mortality in preterm infants. NEC is multifactorial and the result of a complex interaction of feeding, dysbiosis, and exaggerated inflammatory response. Feeding practices in the neonatal intensive care units (NICUs) can vary among institutions and have significant impact on the vulnerable gastointestinal tract of preterm infants. . These practices encompass factors such as the type of feeding and fortification, duration of feeding, and rate of advancement, among others. The purpose of this article is to review the data on some of the most common feeding practices in the NICU and their impact on the development of NEC in preterm infants. Data on the human milk bioactive component glycosaminoglycans, specifically hyaluronan, will also be discussed in the context of postnatal intestinal development and NEC prevention.

Effects of Oral Glutamine Supplementation, Birthweight and Age on Colonic Morphology and Microbiome Development in Male Suckling Piglets

Mortality, impaired development and metabolic dysfunctions of suckling low-birthweight piglets may be influenced by modulating the intestinal microbiome through glutamine supplementation. Therefore, this study examined whether glutamine supplementation may affect the colonic development and microbiome composition of male low- and normal-birthweight piglets at 5 and 12 days of age. Suckling piglets were supplemented orally with glutamine or alanine. Colonic digesta samples were obtained for 16S rDNA sequencing, determination of bacterial metabolites and histomorphological tissue analyses. Glutamine-supplemented piglets had lower concentrations of cadaverine and spermidine in the colonic digesta (p < 0.05) and a higher number of CD3+ colonic intraepithelial lymphocytes compared to alanine-supplemented piglets (p < 0.05). Low-birthweight piglets were characterised by a lower relative abundance of Firmicutes, the genera Negativibacillus and Faecalibacterium and a higher abundance of Alistipes (p < 0.05). Concentrations of cadaverine and total biogenic amines (p < 0.05) and CD3+ intraepithelial lymphocytes (p < 0.05) were lower in low- compared with normal-birthweight piglets. In comparison to the factor age, glutamine supplementation and birthweight were associated with minor changes in microbial and histological characteristics of the colon, indicating that ontogenetic factors play a more important role in intestinal development.

Acceleration of Small Intestine Development and Remodeling of the Microbiome Following Hyaluronan 35 kDa Treatment in Neonatal Mice

The beneficial effects of human milk suppressing the development of intestinal pathologies such as necrotizing enterocolitis in preterm infants are widely known. Human milk (HM) is rich in a multitude of bioactive factors that play major roles in promoting postnatal maturation, differentiation, and the development of the microbiome. Previous studies showed that HM is rich in hyaluronan (HA) especially in colostrum and early milk. This study aims to determine the role of HA 35 KDa, a HM HA mimic, on intestinal proliferation, differentiation, and the development of the intestinal microbiome. We show that oral HA 35 KDa supplementation for 7 days in mouse pups leads to increased villus length and crypt depth, and increased goblet and Paneth cells, compared to controls. We also show that HA 35 KDa leads to an increased predominance of Clostridiales Ruminococcaceae, Lactobacillales Lactobacillaceae, and Clostridiales Lachnospiraceae. In seeking the mechanisms involved in the changes, bulk RNA seq was performed on samples from the terminal ileum and identified upregulation in several genes essential for cellular growth, proliferation, and survival. Taken together, this study shows that HA 35 KDa supplemented to mouse pups promotes intestinal epithelial cell proliferation, as well as the development of Paneth cells and goblet cell subsets. HA 35 KDa also impacted the intestinal microbiota; the implications of these responses need to be determined.

Glutamine supplementation to prevent morbidity and mortality in preterm infants

BACKGROUND

Glutamine is a conditionally essential amino acid. Endogenous biosynthesis may be insufficient for tissue needs in states of metabolic stress. Evidence exists that glutamine supplementation improves clinical outcomes in critically ill adults. It has been suggested that glutamine supplementation may also benefit preterm infants.

OBJECTIVES

To determine the effects of glutamine supplementation on mortality and morbidity in preterm infants.

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 (CENTRAL, 2015, Issue 12), MEDLINE, EMBASE and Maternity and Infant Care (to December 2015), conference proceedings and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in preterm infants at any time from birth to discharge from hospital.

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 relative risk, typical risk difference and weighted mean difference.

MAIN RESULTS

We identified 12 randomised controlled trials in which a total of 2877 preterm infants participated. Six trials assessed enteral glutamine supplementation and six trials assessed parenteral glutamine supplementation. The trials were generally of good methodological quality. Meta-analysis did not find an effect of glutamine supplementation on mortality (typical relative risk 0.97, 95% confidence interval 0.80 to 1.17; risk difference 0.00, 95% confidence interval -0.03 to 0.02) or major neonatal morbidities including the incidence of invasive infection or necrotising enterocolitis. Three trials that assessed neurodevelopmental outcomes in children aged 18 to 24 months and beyond did not find any effects.

AUTHORS' CONCLUSIONS

The available trial data do not provide evidence that glutamine supplementation confers important benefits for preterm infants.

Glutamine supplementation to prevent morbidity and mortality in preterm infants

BACKGROUND

Glutamine is a conditionally essential amino acid. Endogenous biosynthesis may be insufficient for tissue needs in states of metabolic stress. Evidence exists that glutamine supplementation improves clinical outcomes in critically ill adults. It has been suggested that glutamine supplementation may also benefit preterm infants.

OBJECTIVES

To determine the effects of glutamine supplementation on mortality and morbidity in preterm infants.

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 (CENTRAL, 2015, Issue 12), MEDLINE, EMBASE and Maternity and Infant Care (to December 2015), conference proceedings and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in preterm infants at any time from birth to discharge from hospital.

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 relative risk, typical risk difference and weighted mean difference.

MAIN RESULTS

We identified 12 randomised controlled trials in which a total of 2877 preterm infants participated. Six trials assessed enteral glutamine supplementation and six trials assessed parenteral glutamine supplementation. The trials were generally of good methodological quality. Meta-analysis did not find an effect of glutamine supplementation on mortality (typical relative risk 0.97, 95% confidence interval 0.80 to 1.17; risk difference 0.00, 95% confidence interval -0.03 to 0.02) or major neonatal morbidities including the incidence of invasive infection or necrotising enterocolitis. Three trials that assessed neurodevelopmental outcomes in children aged 18 to 24 months and beyond did not find any effects.

AUTHORS' CONCLUSIONS

The available trial data do not provide evidence that glutamine supplementation confers important benefits for preterm infants.

Enteral L-Arginine and Glutamine Supplementation for Prevention of NEC in Preterm Neonates

Objective. Evaluating the efficacy and safety of arginine and glutamine supplementation in decreasing the incidence of NEC among preterm neonates. Methods. Prospective case-control study done on 75 preterm neonates ≤34 weeks, divided equally into L-arginine group receiving enteral L-arginine, glutamine group receiving enteral glutamine, and control group. Serum L-arginine and glutamine levels were measured at time of enrollment (sample 1), after 14 days of enrollment (sample 2), and at time of diagnosis of NEC (sample 3). Results. The incidence of NEC was 9.3%. There was no difference in the frequency of NEC between L-arginine and control groups (P > 0.05). NEC was not detected in glutamine group; L-arginine concentrations were significantly lower in arginine group than control group in both samples while glutamine concentrations were comparable in glutamine and control groups in both samples. No significant difference was found between groups as regards number of septic episodes, duration to reach full oral intake, or duration of hospital stay. Conclusion. Enteral L-arginine supplementation did not seem to reduce the incidence of NEC. Enteral glutamine may have a preventive role against NEC if supplied early to preterm neonates. However, larger studies are needed to confirm these findings. This work is registered in ClinicalTrials.gov (ClinicalTrials.gov Identifier: NCT01263041).

Glutamine downregulates TLR-2 and TLR-4 expression and protects intestinal tract in preterm neonatal rats with necrotizing enterocolitis

BACKGROUND/PURPOSE

Toll-like receptor (TLR)-4 and TLR-2 play an essential role in the pathogenesis of necrotizing enterocolitis (NEC). In this study, we investigated the protective effect of glutamine (Gln) in an NEC neonatal rat model, and the potential association with TLR-4 and TLR-2 expression in local intestinal tissues.

METHODS

Preterm neonatal rats were randomly divided into 3 groups: normal control; NEC model; and NEC plus Gln intervention. NEC was induced by feeding with artificial milk substitutes, plus exposure to hypoxia and cold stress. All preterm rats were sacrificed at 3 days after birth. The intestinal tissues were taken for pathological analysis. Protein and mRNA expression of TLR-2, TLR-4, and caspase-3 was examined by immunohistochemistry and real-time RT-PCR, respectively.

RESULTS

Compared with the normal control, the NEC neonatal rats showed mucosal injury and upregulated mRNA and protein expression of TLR-2, TLR-4, and caspase-3 in ileum and colon. Gln intervention significantly reduced the mucosal injury and suppressed the upregulated expression of TLR-2, TLR-4, and caspace-3 in the ileum and colon of NEC neonatal rats.

CONCLUSIONS

Gln protects the intestinal tract of NEC neonatal rats, which may be associated with the reduction of TLR-2 and TLR-4 expression in intestines.

Prebiotics in infants for prevention of allergy

BACKGROUND

Prebiotics (commonly oligosaccharides) added to infant feeds have the potential to prevent sensitisation of infants to dietary allergens.

OBJECTIVES

To determine the effect of prebiotic given to infants for the prevention of allergy.

SEARCH METHODS

We performed an updated search in August 2012 of the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 8), MEDLINE, EMBASE, conference proceedings, citations, expert informants and clinical trials registries.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials that compared the use of a prebiotic to no prebiotic, or a specific prebiotic compared to a different prebiotic in infants for prevention of allergy.

DATA COLLECTION AND ANALYSIS

Assessment of trial quality, data extraction and synthesis of data were performed using the standard methods of The Cochrane Collaboration.

MAIN RESULTS

The 2012 update identified 13 studies classified as ongoing or awaiting classification (yet to report allergy outcomes). Forty-three studies were excluded, primarily as no allergy data were reported, although none of these enrolled infants were at high risk of allergy. Four studies enrolling 1428 infants were eligible for inclusion. All studies were at high risk of attrition bias. Allergy outcomes were reported from four months to two years of age.Meta-analysis of two studies (226 infants) found no significant difference in infant asthma although significant heterogeneity was found between studies. Meta-analysis of four studies found a significant reduction in eczema (1218 infants, typical risk ratio 0.68, 95% CI 0.48 to 0.97; typical risk difference -0.04, 95% CI -0.07 to -0.00; number needed to treat to benefit (NNTB) 25, 95% CI 14 to > 100; P = 0.03). No statistically significant heterogeneity was found between studies. One study reported no significant difference in urticaria.No statistically significant subgroup differences were found according to infant risk of allergy or type of infant feed. However, individual studies reported a significant reduction in asthma and eczema from supplementation with a mixture of galacto- and fructo-oligosaccharide (GOS/FOS 9:1 ratio) (8 g/L) in infants at high risk of allergy; and in eczema from supplementation with GOS/FOS (9:1) (6.8 g/L) and acidic oligosacccharide (1.2 g/L) in infants not selected for allergy risk.

AUTHORS' CONCLUSIONS

Further research is needed before routine use of prebiotics can be recommended for prevention of allergy in formula fed infants. There is some evidence that a prebiotic supplement added to infant feeds may prevent eczema. It is unclear whether the use of prebiotic should be restricted to infants at high risk of allergy or may have an effect in low risk populations; or whether it may have an effect on other allergic diseases including asthma.

Efficacy and safety of a parenteral amino acid solution containing alanyl-glutamine versus standard solution in infants: a first-in-man randomized double-blind trial

BACKGROUND & AIMS

Efforts are directed at reaching the optimal composition of pediatric amino acids (AA) infusions. The goal was to demonstrate the safety and efficacy of a newly developed parenteral AA solution containing alanyl-glutamine (GLN-AA) compared to Standard-AA.

METHODS

This is a randomized (2:1), double-blind, multicentre clinical pilot trial. Infants after surgical interventions were allocated to receive GLN-AA or Standard-AA over a minimum of 5 days to maximum of 10 days. AA profiles in blood samples obtained at baseline, day 7, and end of treatment were compared to normal ranges. Data regarding safety, and efficacy were also collected.

RESULTS

Infants were comparable for (safety population) gestational age at birth (36 vs 38 weeks), birth weight (2460 vs 2955 g), and day of life during start intervention (1 vs 2 days). Plasma AA profiles in infants treated with GLN-AA (n = 13) were closer the normal ranges than those in infants treated with Standard-AA (n = 6). There were no clinical or statistical differences in adverse events, safety and efficacy parameters between both groups.

CONCLUSION

This first-in-man study shows that GLN-AA is safe in infants after surgical interventions, and is well tolerated. Compared to reference values, GLN-AA better reflects the amino acid requirements of the infant.

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 to prevent morbidity and mortality in preterm infants

BACKGROUND

Glutamine is a conditionally essential amino acid. Endogenous biosynthesis may be insufficient for tissue needs in states of metabolic stress. Evidence exists that glutamine supplementation improves clinical outcomes in critically ill adults. It has been suggested that glutamine supplementation may also benefit preterm infants.

OBJECTIVES

To determine the effects of glutamine supplementation on mortality and morbidity in preterm infants.

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, 2011, Issue 4), 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 preterm infants at any time from birth to discharge from hospital.

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 relative risk, typical risk difference and weighted mean difference.

MAIN RESULTS

We identified 11 randomised controlled trials in which a total of 2771 preterm infants participated. Five trials assessed enteral glutamine supplementation and six trials assessed parenteral glutamine supplementation. The trials were generally of good methodological quality. Meta-analysis did not detect a statistically significant effect of glutamine supplementation on mortality [typical relative risk 0.98 (95% confidence interval 0.80 to 1.18); risk difference 0.00 (95% confidence interval -0.03 to 0.02)] or major neonatal morbidities including the incidence of invasive infection or necrotising enterocolitis. Two trials that assessed neurodevelopmental outcomes at 18 to 24 months did not find any statistically significant differences in various assessments.

AUTHORS' CONCLUSIONS

The available trial data do not provide evidence that glutamine supplementation confers important benefits for preterm infants.

Assessment of intestinal permeability in (premature) neonates by sugar absorption tests

Infants born prematurely have an enhanced intestinal permeability compared to healthy term infants. This enhanced permeability might be a contributing factor in the development of Necrotising Enterocolitis. The assessment of intestinal permeability in premature neonates with sugar absorption tests has been proven to be safe and of minimal burden to the infant. After enteral administration of a test solution containing lactulose and mannitol, the excretion of these sugars is measured in urine, and the ratio is calculated. The lactulose and mannitol concentrations in urine can be measured by the use of a gas chromatograph after pre-purification and derivatisation of the sample. Non-invasive assessment of intestinal permeability can be useful in monitoring the effects of experimental (nutritional) therapy.

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.

The impact of oral glutamine supplementation on the intestinal permeability and incidence of necrotizing enterocolitis/septicemia in premature neonates

OBJECTIVE

To examine the impact of oral glutamine (Gln) supplementation on gut integrity and on the incidence of necrotizing enterocolitis (NEC)/septicemia of premature neonates.

METHODS

Preterm neonates (n = 101, gestational age <34 weeks, birth weight <2000 g) were randomly allocated to receive from day 3 to day 30 postpartum, either oral Gln (0.3 g/kg/day, n = 51-Gln group) or placebo (caloreen-isocaloric, n = 50-control group). Intestinal permeability was determined from the urinary lactulose/mannitol recovery (L/M ratio) following their oral administration and assessed at three time points: day 2 (before first administration), day 7 and day 30 of life. The incidence of NEC and septicemia over the study period was also recorded.

RESULTS

A decrease of lactulose recovery at days 7 (p = 0.001) and 30 (p < 0.001) and a decrease of L/M ratio at day 7 (p = 0.002) were observed only in the Gln group. Lactulose recovery and L/M ratio at day 7 (p = 0.022 and p = 0.004, respectively), as well as lactulose recovery (p = 0.001), mannitol recovery (p = 0.042), and L/M ratio (p = 0.001) at day 30, were decreased in the Gln group as compared to controls. NEC and septicemia were lower in the Gln group at the end of the first week (p = 0.009 and p = 0.041, respectively) and up to the end of the study (p < 0.001 and p = 0.048, respectively).

CONCLUSION

Oral Gln administration may have beneficial effects on intestinal integrity and the overall incidence of NEC/septicemia in preterm infants.

Advances in research of intestinal epithelial tight junctions and intestinal permeability

Intestinal epithelial tight junctions are a structural basis for the intestinal barrier and play an important role in the regulation of intestinal permeability. Increased intestinal permeability caused by the destruction of tight junctions may result in bacterial translocation, systemic inflammatory response, and multiple organ dysfunction syndrome. In this paper, we review the structure and function of tight junctions, factors affecting intestinal permeability, and measures for improving the dysfunction in intestinal permeability.

The effect of enteral supplementation of a prebiotic mixture of non-human milk galacto-, fructo- and acidic oligosaccharides on intestinal permeability in preterm infants

Preterm infants have an impaired gut barrier function. We aimed to determine the effects of enteral supplementation of a prebiotic mixture consisting of neutral oligosaccharides (short-chain galacto-oligosaccharides (SCGOS)/long-chain fructo-oligosaccharides (LCFOS)) and acidic oligosaccharides (AOS) on intestinal permeability of preterm infants as measured by the sugar absorption test in the first week of life. Furthermore, we determined host- and treatment-related factors associated with intestinal permeability. In a randomised controlled trial, preterm infants with a gestational age < 32 weeks and/or birth weight (BW) < 1500 g received enteral supplementation of SCGOS/LCFOS/AOS or placebo (maltodextrin) between days 3 and 30 of life. Intestinal permeability, reflected by the urinary lactulose/mannitol (L/M) ratio after oral ingestion of lactulose and mannitol, was assessed at three time points: before the start of the study (t = 0), at day 4 (t = 1) and at day 7 (t = 2) of life. Data were analysed by generalised estimating equations. In total, 113 infants were included. Baseline patient and nutritional characteristics were not different between the SCGOS/LCFOS/AOS (n 55) and the placebo groups (n 58). SCGOS/LCFOS/AOS had no effect on the L/M ratio between t = 0 and t = 2. In both the groups, the L/M ratio decreased from t = 0 to t = 2 (P < 0·001). Low BW increased the L/M ratio (P = 0·002). Exclusive breast milk feeding and mixed breast milk/formula feeding during the first week of life decreased the L/M ratio (P < 0·001 and P < 0·05, respectively). In conclusion, enteral supplementation of a prebiotic mixture does not enhance the postnatal decrease in intestinal permeability in preterm infants in the first week of life.

Glutamine deprivation alters intestinal tight junctions via a PI3-K/Akt mediated pathway in Caco-2 cells

Glutamine (Gln) is important for intestinal barrier function and regulation of tight junction (TJ) proteins, but the intracellular mechanisms of action remain undefined. The purpose of this study was to test the hypothesis that Gln regulates intercellular junction integrity and TJ proteins through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway in Caco-2 cells. Deprivation of exogenous and endogenous glutamine decreased transepithelial electrical resistance (TER) (P < 0.01) and increased permeability (P < 0.01). Both wortmannin and LY294002, PI3K inhibitors, prevented the TER decrease and the permeability increase induced by Gln deprivation (P < 0.001). Gln deprivation also caused decreased TJ protein claudin-1 (P < 0.001). Both wortmannin and LY294002 treatment prevented this effect (P < 0.001). Deprivation of Gln increased phosphor-Akt protein. Gln supplementation reversed this effect. Decreased TER and increased permeability associated with Gln deprivation were not observed in small interfering RNA for p85 transfected Caco-2 cells. In conclusion, Gln regulates intercellular junction integrity and TJ proteins through the PI3-Kinase/Akt pathway.

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.

Biostatistics primer: part I

Biostatistics is the application of statistics to biologic data. The field of statistics can be broken down into 2 fundamental parts: descriptive and inferential. Descriptive statistics are commonly used to categorize, display, and summarize data. Inferential statistics can be used to make predictions based on a sample obtained from a population or some large body of information. It is these inferences that are used to test specific research hypotheses. This 2-part review will outline important features of descriptive and inferential statistics as they apply to commonly conducted research studies in the biomedical literature. Part 1 in this issue will discuss fundamental topics of statistics and data analysis. Additionally, some of the most commonly used statistical tests found in the biomedical literature will be reviewed in Part 2 in the February 2008 issue.

Glutamine supplementation to prevent morbidity and mortality in preterm infants

BACKGROUND

Glutamine endogenous biosynthesis may be insufficient for tissue needs in states of metabolic stress. Trials in adults have suggested that glutamine supplementation improves clinical outcomes in critically ill adults. It has been suggested that glutamine supplementation may benefit preterm infants, particularly very low birth weight infants.

OBJECTIVES

To determine the effects of glutamine supplementation on mortality and morbidity in preterm infants.

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, 2007), MEDLINE (1966 - July 2007), EMBASE (1980 - July 2007), conference proceedings, and previous reviews.

SELECTION CRITERIA

Randomised or quasi-randomised controlled trials that compared glutamine supplementation versus no glutamine supplementation in preterm infants at any time from birth to discharge from hospital.

DATA COLLECTION AND ANALYSIS

The standard methods of the Cochrane Neonatal Review Group were used, with separate evaluation of trial quality and data extraction by two authors. Data were synthesised using a fixed effects model and reported using typical relative risk, typical risk difference and weighted mean difference.

MAIN RESULTS

2365 preterm infants have participated in seven randomised controlled trials. All of the participating infants were of very low birth weight. Three trials assessed enteral glutamine supplementation and four trials assessed parenteral glutamine supplementation. The trials were generally of good methodological quality with adequate allocation concealment, blinding of caregivers and assessors to the intervention, and complete or near-complete follow-up of recruited infants. Glutamine supplementation does not have a statistically significant effect on mortality: typical relative risk 0.98 (95% confidence interval 0.80 to 1.20); typical risk difference 0.00 (95% confidence interval -0.03 to 0.02). The only trial that assessed long-term outcomes did not find any statistically significant differences in various assessments of neurodevelopment at 18 months corrected age. Glutamine supplementation does not have a statistically significant effect on other neonatal morbidities including invasive infection, necrotising enterocolitis, time to achieve full enteral nutrition, or duration of hospital stay.

AUTHORS' CONCLUSIONS

The available data from good quality randomised controlled trials indicate that glutamine supplementation does not confer benefits for preterm infants. The narrow confidence intervals for the effect size estimates suggest that a further trial of this intervention is not a research priority.

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.