The effect of early postnatal auditory stimulation on outcomes in preterm infants.

Preterm infants are deprived of in utero sensory stimulation during the third trimester, an important period of central nervous system development. As a result, maturational trajectories are often reduced in infants born preterm. One such system affected is the brain including the auditory and respiratory control pathways. During normal pregnancy the intrauterine environment attenuates external auditory stimuli while exposing the fetus to filtered maternal voice, intra-abdominal sounds, and external stimuli. In contrast, during the third trimester of development, preterm infants are exposed to a vastly different soundscape including non-attenuated auditory sounds and a lack of womb related stimuli, both of which may affect postnatal brain maturation. Therefore, fostering a nurturing postnatal auditory environment during hospitalization may have a significant impact on related outcomes of preterm infants. Studies using a range of postnatal auditory stimulations have suggested that exposure to sounds or lack thereof can have a significant impact on outcomes. However, studies are inconsistent with sound levels, duration of exposure to auditory stimuli, and the gestational age at which infants are exposed. IMPACT: Auditory stimulation can provide a low cost and low risk intervention to stabilize respiration, improve neuronal maturation and reduce long-term sequelae in preterm infants. The potential benefits of auditory stimulation are dependent on the type of sound, the duration of exposure and age at time of exposure. Future studies should focus on the optimal type and duration of sound exposure and postnatal developmental window to improve outcomes.

Choline supplementation mitigates effects of bilirubin in cerebellar granule neurons in vitro.

BACKGROUND: Premature infants may suffer from high levels of bilirubin that could lead to neurotoxicity. Bilirubin has been shown to decrease L1-mediated ERK1/2 signaling, L1 phosphorylation, and L1 tyrosine 1176 dephosphorylation. Furthermore, bilirubin redistributes L1 into lipid rafts (LR) and decreases L1-mediated neurite outgrowth. We demonstrate that choline supplementation improves L1 function and signaling in the presence of bilirubin. METHODS: Cerebellar granule neurons (CGN) were cultured with and without supplemental choline, and the effects on L1 signaling and function were measured in the presence of bilirubin. L1 activation of ERK1/2, L1 phosphorylation and dephosphorylation were measured. L1 distribution in LR was quantified and neurite outgrowth of CGN was determined. RESULTS: Forty µM choline significantly reduced the effect of bilirubin on L1 activation of ERK1/2 by 220% (p = 0.04), and increased L1 triggered changes in tyrosine phosphorylation /dephosphorylation of L1 by 34% (p = 0.026) and 35% (p = 0.02) respectively. Choline ameliorated the redistribution of L1 in lipid rafts by 38% (p = 0.02) and increased L1-mediated mean neurite length by 11% (p = 0.04). CONCLUSION: Choline pretreatment of CGN significantly reduced the disruption of L1 function by bilirubin. The supplementation of pregnant women and preterm infants with choline may increase infant resilience to the effects of bilirubin. IMPACT: This article establishes choline as an intervention for the neurotoxic effects of bilirubin on lipid rafts. This article provides clear evidence toward establishing one intervention for bilirubin neurotoxicity, where little is understood. This article paves the way for future investigation into the mechanism of the ameliorative effect of choline on bilirubin neurotoxicity.

Neonatal hypoxia ischemia redistributes L1 cell adhesion molecule into rat cerebellar lipid rafts.

BACKGROUND: Hypoxic-ischemic encephalopathy (HIE) is a devastating disease with lifelong disabilities. Hypothermia is currently the only treatment. At term, the neonatal cerebellum may be particularly vulnerable to the effects of HIE. At this time, many developmental processes depend on lipid raft function. These microdomains of the plasma membrane are critical for cellular signaling and axon extension. We hypothesized that HIE alters the protein content of lipid rafts in the cerebellum. METHODS: Postnatal day (PN) 10 animals, considered human term equivalent, underwent hypoxic-ischemic (HI) injury by a right carotid artery ligation followed by hypoxia. For some animals, LPS was administered on PN7, and hypothermia (HT) was conducted for 4 h post-hypoxia. Lipid rafts were isolated from the right and left cerebella. The percent of total L1 cell adhesion molecule in lipid rafts was determined 4 and 72 h after hypoxia. RESULTS: No sex differences were found. HI alone caused significant increases in the percent of L1 in lipid rafts which persisted until 72 h in the right but not the left cerebellum. A small but significant effect of LPS was detected in the left cerebellum 72 h after HI. Hypothermia had no effect. CONCLUSIONS: Lipid rafts may be a new target for interventions of HIE. IMPACT: This article investigates the effect of neonatal exposure to hypoxic-ischemic encephalopathy (HIE) on the distribution of membrane proteins in the cerebellum. This article explores the effectiveness of hypothermia as a prevention for the harmful effects of HIE on membrane protein distribution. This article shows an area of potential detriment secondary to HIE that persists with current treatments, and explores ideas for new treatments.

Choline supplementation prevents the effects of bilirubin on cerebellar-mediated behavior in choline-restricted Gunn rat pups.

BACKGROUND: Bilirubin is produced by the breakdown of hemoglobin and is normally catabolized and excreted. Neurotoxic accumulation of serum bilirubin often occurs in premature infants. The homozygous Gunn rat lacks uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), the enzyme needed to biotransform bilirubin. This rodent model of hyperbilirubinemia emulates many aspects of bilirubin toxicity observed in the human infant. We demonstrate that choline supplementation in early postnatal development is neuroprotective in the choline-restricted Gunn rat, when hyperbilirubinemia is induced on postnatal day 5. METHODS: We first compared behaviors and cerebellar weight of pups born to dams consuming regular rat chow to those of dams consuming choline-restricted diets. Second, we measured behaviors and cerebellar weights of pups born to choline-restricted dams, reared on a choline-restricted diet, supplemented with or without choline, and treated with or without sulfadimethoxine (SDMX). RESULTS: A choline-restricted diet did not change the behavioral outcomes, but cerebellar weight was reduced in the choline-restricted group regardless of genotype or SDMX administration. SDMX induced behavioral deficits in jj pups, and choline supplementation improved most behavioral effects and cerebellar weight in SDMX-treated jj rats. CONCLUSIONS: These results suggest that choline may be used as a safe and effective neuroprotective intervention against hyperbilirubinemia in the choline-deficient premature infant. IMPACT: This article investigates the effect of neonatal jaundice/bilirubin neurotoxicity on cerebellar-mediated behaviors. This article explores the potential use of choline as an intervention capable of ameliorating the effect of bilirubin on the choline-restricted developing brain. This article opens the door for future studies on the action of choline in the presence of hyperbilirubinemia, especially in preterm neonates.

Bilirubin inhibits lipid raft dependent functions of L1 cell adhesion molecule in rat pup cerebellar granule neurons.

BACKGROUND: The mechanism of bilirubin neurotoxicity is poorly understood. We hypothesize that bilirubin inhibits the function of lipid rafts (LR), microdomains of the plasma membrane critical for signal transduction. To test this hypothesis, we measured the effect of free bilirubin (Bf) between 7.6 and 122.5 nM on LR-dependent functions of L1 cell adhesion molecule (L1). METHODS: Cerebellar granule neurons (CGN) were plated on poly-L-lysine overnight, and neurite length was determined after 1 h treatment with L1 alone or L1 and bilirubin. L1 activation of ERK1/2 was measured in CGN in the presence or absence of bilirubin. The effect of bilirubin on L1 distribution in LR was quantitated, and the localization of bilirubin to LR was determined. RESULTS: The addition of bilirubin to CGN treated with L1 significantly decreased neurite length compared to L1 alone. L1 activation of ERK1/2 was inhibited by bilirubin. Bilirubin redistributed L1 into LR. Bilirubin was associated only with LR-containing fractions of a sucrose density gradient. CONCLUSION: Bf significantly inhibits LR-dependent functions of L1 and are found only associated with LR, suggesting one mechanism by which bilirubin may exert neurotoxicity is through the dysfunction of protein-LR interactions. IMPACT: This article establishes lipid rafts as a target for the neurotoxic effects of bilirubin. This article provides clear evidence toward establishing one mechanism of bilirubin neurotoxicity, where little is understood. This article paves the way for future investigation into lipid raft dependent functions, and its role in neurodevelopmental outcome.

A Gunn rat model of preterm hyperbilirubinemia.

BACKGROUND: The impact of bilirubin in preterm infants is poorly understood. An animal model would assist in improving understanding. The Gunn rat lacks uridine diphosphate-glucuronylsyl transferase 1 and can be made acutely hyperbilirubinemic by injection of sulfodimethoxine (sulfa), a drug that displaces bilirubin from albumin and thus increases free bilirubin. METHODS: On postnatal day (P) 5, Gunn rats either heterozygous (Nj) or homozygous (jj) for glucuronosyltransferase activity were injected with either saline or sulfa. Behavior and cerebellar weight were measured. RESULTS: Pups did not show any signs of acute bilirubin encephalopathy. Pup weight dropped significantly on P8 only in the jj-sulfa group. Behavior was affected only in the jj-sulfa group. Cerebellar weight was significantly less in the jj-sulfa group. CONCLUSION: The Gunn rat pup model may be a good model to study hyperbilirubinemia in preterm infants.

Mercury, lead, and cadmium exposure via red blood cell transfusions in preterm infants.

BACKGROUND: Mercury, lead, and cadmium are developmental neurotoxicants. We predict that preterm newborns requiring packed red blood cell (PRBC) transfusions may be exposed to neurotoxic doses. We explored the relationship between donor concentration, number of donors, number of transfusions and mercury, lead and cadmium exposure. METHODS: Single-donor PRBCs were analyzed for mercury, lead and cadmium concentration. Dose per transfusion was calculated and compared to intravenous reference doses (IVRfDs). Linear regression analyses were performed to correlate donor and infant exposure. RESULTS: Thirty-six infants received 268 transfusions from 94 donors. Number of donors and transfusions were significantly correlated with birthweight and gestational age. All three metals were detected in ≥95% of donor PRBCs. Number of donors was significantly associated with cumulative dose, and there was a significant correlation between mercury and lead doses/transfusion. IVRfDs were exceeded for mercury and lead in 8.6% and 38% of transfusions, respectively. None exceeded the IVRfD for cadmium. For lead, infants exposed to three donors had more transfusions exceeding IVRfD than those exposed to 1-2 donors. CONCLUSIONS: Preterm infants are exposed to heavy metals via transfusions. Doses exceeded the IVRfDs for mercury and lead. Cadmium did not pose a risk. Prescreening donor blood could reduce exposure risk.

High concentrations of urinary ethanol metabolites in neonatal intensive care unit infants.

BACKGROUND: Infants in the neonatal intensive care unit may be exposed to ethanol via medications that contain ethanol as an excipient and through inhalation of ethanol vapor from hand sanitizers. We hypothesized that both pathways of exposure would result in elevated urinary biomarkers of ethanol. METHODS: Urine samples were collected from infants in incubators and in open cribs. Two ethanol metabolites, ethyl sulfate (EtS) and ethyl glucuronide (EtG), were quantified in infants' urine. RESULTS: A subset of infants both in incubators and open cribs had ethanol biomarkers greater than the cutoff concentration that identifies adult alcohol consumption. These concentrations were associated with the infant having received an ethanol-containing medication on the day of urine collection. When infants who received an ethanol-containing medication were excluded from analysis, there was no difference in ethanol biomarker concentrations between the incubator and crib groups. CONCLUSIONS: Some infants who received ethanol-containing medications had concentrations of ethanol biomarkers that are indicative of adult alcohol consumption, suggesting potential exposure via ethanol excipients. IMPACT: Infants and newborns in the neonatal intensive care unit are exposed to concerning amounts of ethanol. No one has shown exposure to ethanol in these infants before this study. The impact is that better understanding of the excipients in medications given to patients in the NICU is needed. When physicians order medications in the NICU, the amount of excipient needs to be indicated.

Fetal exposure to mercury and lead from intrauterine blood transfusions.

BACKGROUND: Mercury (Hg) and lead (Pb) exposure during childhood is associated with irreversible neurodevelopmental effects. Fetal exposure to Hg and Pb from intrauterine blood transfusion (IUBT) has not been reported. METHODS: Fetal exposure was estimated based on transfusion volume and metal concentration in donor packed red blood cell (PRBCs). As biomarkers to quantify prenatal exposure are unknown, Hg and Pb in donor PRBCs were compared to estimated intravenous (IV) RfDs based on gastrointestinal absorption. RESULTS: Three pregnant women received 8 single-donor IUBTs with volumes ranging from 19 to 120 mL/kg. Hg and Pb were present in all donor PRBC units. In all, 1/8 IUBT resulted in Hg dose five times higher than the estimated IV RfD. Median Pb dose in one fetus who received 5 single-donor IUBTs between 20-32 weeks gestation was 3.4 µg/kg (range 0.5-7.9 µg/kg). One donor unit contained 12.9 µg/dL of Pb, resulting in a fetal dose of 7.9 µg/kg, 40 times higher than the estimated IV RfD at 20 weeks gestation. CONCLUSION: This is the first study documenting inadvertent exposure to Hg and Pb from IUBT and quantifying the magnitude of exposure. Screening of donor blood is warranted to prevent toxic effects from Hg and Pb to the developing fetus.

Urinary metabolites of volatile organic compounds of infants in the neonatal intensive care unit.

BackgroundPreterm infants (PTI) in the NICU are often placed in incubators that may increase their exposure to volatile organic chemicals (VOCs). To determine whether PTI in incubators have higher urinary concentrations of VOC metabolites compared with infants in cribs.MethodsUrine from 40 PTI in incubators and 40 infants in cribs was collected and analyzed for 28 urinary VOC biomarkers. Differences in metabolite concentrations between the two groups were compared.ResultsTwenty two of the VOC metabolites were detected in at least one urine sample. All urine samples tested had measurable levels of six VOC metabolites. Biomarkers for acrolein, acrylonitrile, carbon disulfide, cyanide, N-dimethylformamide, ethylbenzene, ethylene oxide, propylene oxide, styrene, toluene/benzyl alcohol, vinyl chloride, and xylene were higher in the incubator group. The geometric means of five VOC metabolites were 2-fold higher than those reported for NHANES children 6-11 years of age in one or both of the groups with benzyl mercapturic acid being 7-fold and 12-fold greater than NHANES in the crib and incubator group, respectively.ConclusionAll infants were exposed to VOCs. PTI in incubators have a different VOC exposure profile compared with infants in cribs. The health implications associated with these exposures require further study.