Clotilde Des Robert

Early Intestinal Bacterial Colonization and Necrotizing Enterocolitis in Premature Infants: The Putative Role of Clostridium

Necrotizing enterocolitis (NEC) is among the most severe conditions that can affect preterm infants. Although the etiology of NEC remains unknown, initial bacterial colonization could play a pivotal role in the development of NEC. To further explore the putative relationship between pathogen microorganisms and NEC, we conducted a prospective case-control study in 12 preterm infants with a new approach based on molecular techniques. Over an inclusion period of 24 mo, 12 neonates of <34 wk gestational age admitted to the neonatal unit were enrolled. The group included three cases of NEC, and nine control infants without evidence of NEC who were matched for gestational age and birth weight. Stool samples were collected at weekly intervals from all infants. PCR and temporal temperature gradient gel electrophoresis of 16S ribosomal DNA were used to detect the establishment of bacterial communities in the digestive tract. A salient feature of the bacteriological pattern was observed only in the three infants who later developed NEC: A band corresponding to the Clostridium perfringens subgroup could be detected in early samples, before diagnosis. There was no evidence for this specific band in any of the nine controls. To our knowledge, the current report is the first to demonstrate that the use of molecular techniques based on the study of bacterial 16S rRNA genes allowed the recognition of C. perfringens species in the first 2 wk of life of three infants who later displayed symptoms of NEC. A significant temporal relationship was thus established between early colonization by Clostridium and the later development of NEC. Compared with conventional bacteriological culturing methods, the use of this new molecular approach to analyze the gastrointestinal ecosystem should therefore allow a more complete and rapid assessment of intestinal flora. Although the current data do not constitute definitive proof that the identified bacterial species was a causative agent in the development of NEC, they outline the promise of this new technique based on molecular biology, and suggest that large-scale studies on a much wider population at high risk for NEC may be warranted.

Oral supplementation with probiotics in very-low-birth-weight preterm infants: a randomized, double-blind, placebo-controlled trial

BACKGROUND Although recent reports suggest that supplementation with probiotics may enhance intestinal function in premature infants, the mechanisms are unclear, and questions remain regarding the safety and efficacy of probiotics in extremely low-birth-weight infants. OBJECTIVE The objective was to evaluate the efficacy of probiotics on the digestive tolerance to enteral feeding in preterm infants born with a very low or extremely low birth weight. DESIGN In a bicentric, double-blind, randomized controlled clinical trial that was stratified for center and birth weight, 45 infants received enteral probiotics (Bifidobacterium longum BB536 and Lactobacillus rhamnosus GG; BB536-LGG) and 49 received placebo. The primary endpoint was the percentage of infants receiving >50% of their nutritional needs via enteral feeding on the 14th day of life. A triangular test was used to perform sequential analysis. RESULTS The trial was discontinued after the fourth sequential analysis concluded a lack of effect. The primary endpoint was not significantly different between the probiotic (57.8%) and placebo (57.1%) groups (P = 0.95). However, in infants who weighed >1000 g, probiotic supplementation was associated with a shortening in the time to reach full enteral feeding (P = 0.04). Other than colonization by the probiotic strains, no alteration in the composition of intestinal microbiota or changes in the fecal excretion of calprotectin was observed. No colonization by probiotic strains was detected in infants who weighed < or =1000 g, presumably because of more frequent suspensions of enteral feeding, more courses of antibiotic treatment, or both. CONCLUSIONS Supplementation with BB536-LGG may not improve the gastrointestinal tolerance to enteral feeding in very-low-birth-weight infants but may improve gastrointestinal tolerance in infants weighing >1000 g. This trial was registered at clinicaltrials.gov as NCT 00290576.

Acute Effects of Intravenous Glutamine Supplementation on Protein Metabolism in Very Low Birth Weight Infants: A Stable Isotope Study

Although very low birth weight infants are subjected to severe stress and glutamine is now considered a conditionally essential amino acid that may attenuate stress-induced protein wasting in adults, current amino acid solutions designed for neonatal parenteral nutrition do not contain glutamine. To determine whether a short-term supplementation with i.v. glutamine would affect protein metabolism in very low birth weight infants, 13 preterm neonates (gestational age, 28–30 wk; birth weight, 820–1610 g) receiving parenteral nutrition supplying 1.5 g · kg−-1 · d−1 amino acids and approximately 60 nonprotein kcal · kg−1 · d−1 were randomized to receive an i.v. supplement made of either 1) natural l-glutamine (0.5 g · kg−1 · d−1; glutamine group), or 2) an isonitrogenous glutamine-free amino acid mixture (control group), for 24 h starting on the third day of life. On the fourth day of life, they received a 2-h infusion of NaH13CO3 to assess the recovery of 13C in breath, immediately followed by a 3-h l-[1-13C]leucine infusion. Plasma ammonia did not differ between the groups. Glutamine supplementation was associated with 1) higher plasma glutamine (629 ± 94 versus 503 ± 83 μM, mean ± SD;p < 0.05, one-tailed unpaired t test), 2) lower rates of leucine release from protein breakdown (−16%, p < 0.05) and leucine oxidation (−35%, p < 0.05), 3) a lower rate of nonoxidative leucine disposal, an index of protein synthesis (−20%, p < 0.05), and 4) no change in protein balance (nonoxidative leucine disposal − leucine release from protein breakdown, NS). We conclude that although parenteral glutamine failed to enhance rates of protein synthesis, glutamine may have an acute protein-sparing effect, as it suppressed leucine oxidation and protein breakdown, in parenterally fed very low birth weight infants.

Structural and optical analyses of GaP/Si and (GaAsPN/GaPN)/GaP/Si nanolayers for integrated photonics on silicon

We report a structural study of molecular beam epitaxy-grown lattice-matched GaP/Si(0 0 1) thin layers with an emphasis on the interfacial structural properties, and optical studies of GaAsP(N)/GaP(N) quantum wells coherently grown onto the GaP/Si pseudo substrates, through a complementary set of characterization tools. Room temperature photoluminescence at 780 nm from the (GaAsPN/GaPN) quantum wells grown onto a silicon substrate is reported. Despite this good property, the time-resolved photoluminescence measurements demonstrate a clear influence of non-radiative defects initiated at the GaP/Si interface. It is shown from simulations, how x-ray diffraction can be used efficiently for analysis of antiphase domains. Then, qualitative and quantitative analyses of antiphase domains, micro-twins, and stacking faults are reported using complementarity of the local transmission electron microscopy and the statistical x-ray diffraction approaches.

Enabling valley selective exciton scattering in monolayer WSe2 through upconversion.

Excitons, Coulomb bound electron–hole pairs, are composite bosons and their interactions in traditional semiconductors lead to condensation and light amplification. The much stronger Coulomb interaction in transition metal dichalcogenides such as WSe2 monolayers combined with the presence of the valley degree of freedom is expected to provide new opportunities for controlling excitonic effects. But so far the bosonic character of exciton scattering processes remains largely unexplored in these two-dimensional materials. Here we show that scattering between B-excitons and A-excitons preferably happens within the same valley in momentum space. This leads to power dependent, negative polarization of the hot B-exciton emission. We use a selective upconversion technique for efficient generation of B-excitons in the presence of resonantly excited A-excitons at lower energy; we also observe the excited A-excitons state 2s. Detuning of the continuous wave, low-power laser excitation outside the A-exciton resonance (with a full width at half maximum of 4 meV) results in vanishing upconversion signal.

Evaluation of InGaPN and GaAsPN materials lattice-matched to Si for multi-junction solar cells

We compare the potentiality of bulk InGaPN and GaAsPN materials quasi-lattice-matched to silicon (Si), for multi-junction solar cells application. Bandgaps of both bulk alloys are first studied by a tight-binding model modified for nitrogen incorporation in diluted regimes. The critical thicknesses of those alloys are then calculated for various compositions. For the same lattice-mismatch and nitrogen amount, the bandgap of bulk GaAsPN is found to be closer to the targeted gap value of 1.7 eV for high efficiency tandem solar cell. GaPN and GaAsPN epilayers are then grown by molecular beam epitaxy on GaP substrate and studied by photoluminescence and X-ray diffraction. A GaAsPN bulk alloy emitting light at 1.77 eV at room temperature is obtained, demonstrating promising properties for further use in III-V/Si photovoltaic multijunction solar cells.

Metabolic effects of different protein intakes after short term undernutrition in artificially reared infant rats.

BACKGROUND Early postnatal nutrition is involved in metabolic programming. Small for gestational age and premature babies commonly receive insufficient dietary protein during the neonatal period due to nutrition intolerance, whereas high protein formulas are used to achieve catch up growth. Neither the short term, nor the long term effects of such manipulation of protein intake are known. AIM We hypothesized that high or low protein intake during infancy would induce metabolic alterations both during early-life and in adulthood. METHODS Gastrostomized neonatal rat pups received either 50% (P50%), 100% (P100%), or 130% (P130%) of the normal protein content in rat milk from the 7th to the 15th day of life (D7 to D15), when they were either sacrificed or placed with mothers for the long term study. Glucose tolerance tests (GTT) were performed at D230. Long term rats were sacrificed at D250. RESULTS At D15, weight of P50% pups was lower than P100% and P130% pups. Neither liver and kidney mass, nor islet beta-cell areas were altered. Brain weight (adjusted to body weight) was higher in P50% vs. P130% (p<0.05). Insulin/glucose ratio was lower in P50% vs. P130%. Expression of GLUT4 on adipocyte cell membrane and GLUT2 in liver cytosol was significantly enhanced in P50% vs. P130%. Long term, neither GTT results nor body nor organ weights differed between groups. CONCLUSION In neonatal rats, higher protein intakes via the enteral route led to enhanced short term weight gain, insulin resistance, and modified expression of glucose transporters. However, these differences were not sustained.

Room temperature photoluminescence of high density (In,Ga)As/GaP quantum dots

We report on the achievement of high density (In,Ga)As self-assembled quantum dots on GaP substrate with a good homogeneity. Good structural and electronic properties have been achieved, as revealed by room temperature photoluminescence measurements and by comparison to both InAs/GaAs and InAs/InP materials reference systems. This is supported by atomistic calculations where the indium incorporation in InGaAs/GaP quantum structures is found to enhance both the type-I bandlineup and direct bandgap properties. The photoluminescence temperature dependence of the bandgap evidences the quantum confinement effects. Our results provide a valid framework to implement silicon optical devices based on InGaAs/GaP nanostructures.

Recovery of Exfoliated Cells From the Gastrointestinal Tract of Premature Infants: A New Tool to Perform “Noninvasive Biopsies?”

To gain insight into specific gene expression in the gastrointestinal (GI) tract of preterm infants, we adapted a method to isolate exfoliated epithelial cells. Gastric residual fluid aspirates (n = 89) or stool samples (n = 10) were collected from 96 neonates (gestational age, 24–36 wk). Cells were characterized by microscopic observation, cytokeratin-18 immunodetection, and expression of transcripts. The human origin of cellular DNA was confirmed by amplification of specific X and Y chromosome sequences. Isolation yielded 100–500 cells per sample for gastric aspirates (n = 8) and 10–20 cells for fecal samples (n = 5). Epithelial origin was confirmed by immunodetection of cytokeratin 18. Analyses of reverse transcribed products, using two independent methods, from 15 gastric fluid and two stool samples showed that 18S-rRNA and transcripts of beta-actin, glyceraldehyde-3-phosphate dehydrogenase (gapdh), and period1 were in quantities corresponding to at least 10 cells. On 59 aspirates, we found beta-actin transcripts (all but one), cytokeratin 18 (eight positive of eight samples), SLC26-A7-1 (13 positive of 19 samples), period2 (17 positive of 17 samples), and clock (25 positive of 26 samples). Exfoliated cells can be recovered from gastric aspirates and fecal samples and serve as a tool to investigate the impact of therapeutic and nutritional regimens on the maturation of GI functions.

Neonatal Formula Feeding Leads to Immunological Alterations in an Animal Model of Type 1 Diabetes

Neonatal diet may influence the development of type 1 diabetes (T1D) in susceptible individuals through an intestinal mucosal inflammatory response, resulting in loss of self-tolerance. We tested the hypothesis that formula feeding during the neonatal period accelerates the development of T1D in diabetes-prone BioBreeding (BBDP) rats through regulation of CD4+CD25+ regulatory T lymphocytes (Treg) and anti-inflammatory cytokines. BBDP rat pups fed rat milk substitute (RMS) via a “pup-in-the cup” system were compared with mother-fed (MF) rats. The spleen and thymus were analyzed for Foxp3-expressing CD4+/CD25+ T cells. Multiplex enzyme-linked immunosorbent assays (ELISAs) were performed to measure cytokine-induced neutrophil chemoattractant (CINC), tumor necrosis factor α (TNF-α), interferon-gamma (IFN-γ), interleukin (IL)-4, IL-10, and IL-18. Diabetes-free survival, time of disease onset, and Treg/total T lymphocyte ratios were not different. MF pups had higher ileal CINC (p < 0.001) and IL-18 (p = 0.002), but no differences in the liver. There were no differences in ileal cytokine concentrations of 75-d-old rats, but the formula-fed rats had greater liver TNF-α (p < 0.001), IFN-γ, and IL-4 (p < 0.01) and lower IL-10 (p = 0.002) compared with MF animals. Formula versus maternal milk altered the hepatic cytokine profile at 75 d toward an inflammatory pattern but did not result in altered Treg cell frequencies or the development of T1D.