Biology of the neonate最新文献

Background: Perinatal asphyxia is an important cause of neonatal mortality and subsequent serious sequelae such as motor and cognitive deficits and seizures. The ameliorative effect of erythropoietin (Epo) on experimental hypoxic-ischemic brain injury in neonatal rats has been recently reported. Recent studies also confirm the antiapoptotic effect of Epo in a variety of in vitro and in vivo neuronal injury models including hypoxic-ischemic brain injury. However, molecular mechanisms of Epo protection and antiapoptotic effect in this model are unclear. Epo may exert its antiapoptotic effect via the differential regulation of the expression of genes involved in the apoptotic process.

Objectives: Thus, in the present study, we studied the effects of systemically administered Epo on antiapoptotic (bcl-2, bcl-XL), proapoptotic (bax and DP5) gene expression following hypoxic-ischemic brain injury in neonatal rats.

Methods: Seven- day-old Wistar rat pups were divided into three groups: control group (n=15), saline-treated group (n=17), and Epo-treated group (n=18). Rat pups were subjected to left carotid artery occlusion followed by 2.5 h of hypoxic exposure. Epo-treated group received an intraperitoneal injection of recombinant human Epo at a dose of 1,000 units/kg, saline-treated group received an intraperitoneal injection of saline at the same volume of Epo. Forty-eight hours after hypoxia, 3 animals in each group were killed for histopathological evaluation. To detect DNA fragmentation in cell nuclei, terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling reaction was applied. Bcl-2 and bax protein expression were also analyzed with immunohistochemistry. For reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, rats were sacrificed 4, 12, and 24 h after hypoxia. Bcl-2, bcl-XL, bax, and DP5 mRNA expression were analyzed by RT-PCR.

Results: Epo significantly prevented hypoxia-ischemia-induced bax and DP5 mRNA upregulation in brain tissue. Epo did not show any effect on bcl-XL transcription altered by injury. However, Epo reversed injury-induced downregulation in bcl-2 transcription. Modulating effects of Epo on bcl-2 and bax protein expression were also revealed by immunohistochemistry.

Conclusions: These results suggest that Epo exerts a neuroprotective effect against hypoxic-ischemic brain injury, at least partially, via the differential regulation of the expression of genes involved in apoptotic process.

Background: Structural changes in the developing conducting airway impact the rigidity of the airway, altering the airway's ability to sustain its shape during ventilation. The developmental changes in airway compliance oppose the changes in compliance of the developing lung; thus the expression profiles of matrix modeling proteins likely are also opposite in these developing organs.

Objectives: To determine the profiles of matrix metalloproteinases (MMPs) -2, -7, and -9 and tissue inhibitors (TIMPs) -1 and -2 in the developing trachea and test the hypothesis these profiles would contrast those previously reported for the lung.

Methods: Rabbits tracheae were harvested at 21 days of gestation, 3 and 17 days postgestation and at adulthood. Tissue homogenates were analyzed by substrate zymography for the activity of MMPs, and reverse zymography for TIMPs. Immunostainings on neonatal lamb tracheal rings were used to localize MMP-2 and 9.

Results: Analysis revealed an age-dependent decrease in total MMP-2 quantity and the ratio of active to latent forms. TIMP-2 shows a time-dependent increase throughout airway development. Total MMP-9 and TIMP-1 quantities were unchanged across these ages, although MMP-9 protein was found predominantly in its latent form during development and predominantly in its active form during adulthood. Respiratory epithelial cells reacted positive for both MMP-2 and 9 and trachealis muscle fibers were positive for MMP-2. No MMP-7 expression was identified in the rabbit airway.

Conclusions: The opposing developmental patterns in MMP-2 expression between the airway and lung lead to speculation regarding the role of MMP-2 activity on changes in organ compliance.

Exposure to hypoxia during the first weeks of life in newborn rats decreases vascular growth and alveolarization and causes pulmonary hypertension (PH). BAY 41-2272 is a novel direct activator of soluble guanylate cyclase independent of nitric oxide, effective as an acute pulmonary vasodilator in an animal model of persistent pulmonary hypertension of the newborn, but whether prolonged BAY 41-2272 therapy is effective in the setting of chronic PH is unknown. We hypothesize that BAY 41-2272 would prevent PH induced by chronic exposure to neonatal hypoxia. At 2 days of age, newborn rats were randomly exposed to hypoxia (FiO2, 0.12) or room air, and received daily intramuscular treatment with BAY 41-2272 (1 mg/kg) or saline. After 2 weeks, rats were killed for assessment of right ventricular hypertrophy (RVH), wall thickness of small pulmonary arteries, vessels density, radial alveolar counts and mean linear intercepts. In comparison with control, hypoxia increased RVH and artery wall thickness, reduced vessels density, decreased radial alveolar counts and increased mean linear intercepts. In comparison with hypoxic controls, prolonged BAY 41-2272 treatment during chronic hypoxia reduced RVH (0.67 +/- 0.03 vs. 0.52 +/- 0.05; p < 0.05), and attenuated artery wall thickness (48.2 +/- 2.8% vs. 35.7 +/- 4.1 microm; p < 0.01). However, BAY 41-2272 did not change vessels density, radial alveolar counts or mean linear intercepts. We conclude that BAY 41-2272 prevents the vascular structural effects of PH and reduces RVH but does not protect from hypoxia-induced inhibition of alveolarization and vessel growth. We speculate that BAY 41-2272 may provide a new therapy for chronic PH.

Aim: Matrix metalloproteinases (MMPs) play an eminent role in airway injury and remodelling. We explored the hypothesis that pulmonary MMP levels would differ early after birth (2-4 days) between infants with resolving respiratory distress syndrome (RDS) and infants developing chronic lung disease of prematurity (CLD).

Methods: Thirty-two prematurely born infants (gestational age < or =30 weeks) diagnosed with RDS were included. In 13 infants RDS resolved while 19 developed CLD. MMP-2 and MMP-9 in bronchoalveolar lavage (BAL) fluids collected on postnatal days 2, 4, 7 and 10 were analyzed by zymography and densitometry. Immunochemistry was performed on BAL cells and lung tissue to identify cellular sources of MMP-9 in RDS and CLD.

Results: Median MMP-9 levels increased significantly on day 2 in BAL fluid from patients with resolving RDS (median values MMP-9 = 42.0 arbitrary units (AU)) compared to CLD patients (MMP-9 = 5.4 AU). MMP-9 and neutrophil lipocalin-associated MMP-9 (NGAL) were significantly higher on day 4 in BAL fluid from resolving RDS (MMP-9 = 65.8 AU; NGAL = 16.1 AU) compared to CLD (MMP-9 = 25.4 AU; NGAL = 2.0 AU), Levels of MMP-9 and NGAL increased subsequently on days 7 and 10 in CLD. No differences in MMP-2 levels were detected between RDS and CLD. Neutrophils, macrophages and alveolar type-II epithelial cells were identified as potential sources of MMP-9.

Conclusion: Our findings indicate differences in early MMP-9 BAL fluid levels between resolving RDS and developing CLD, which may relate to the ability to raise an early and adequate response to the initial injury.

We hypothesized that enriching surfactant with hyaluronan would restore lung function when tested in a premature animal model. Newborn piglets (85% gestation, term 112-114 days) were delivered by cesarean section, subjected to mechanical ventilation (tidal volume 6- 8 ml/kg) and randomly assigned to treatment with 50 or 100 mg/kg Curosurf (C50 and C100), 50 or 100 mg/kg Curosurf mixed with 2.5% HA (w/w, CH50 and CH100). A ventilated and not treated group (Cont) and a not treated and not ventilated group (Non) were included as controls. Six hours after treatment the lungs were removed and biochemical, biophysical, cytological and histological analyses were carried out. The CH100, CH50, C100 and C50 groups had variable but significantly improved alveolar phospholipid content, minimal surface tension, alveolar aeration and wet/dry lung weight ratios, but little histological evidence of lung injury. CH100, CH50 and C100 groups had the best effects in terms of oxygenation, lung compliance and histology and evidence of decreased inflammation (IL-8 and TNF-alpha mRNA expression). We conclude that HA added to 50 mg/kg Curosurf or use of 100 mg/kg Curosurf with or without HA provides the best effects in terms of lung function and reduction of inflammation.

Background: Doxapram is a respiratory stimulant widely used for the treatment of idiopathic apnea of prematurity, although it has been demonstrated that it can induce a transient decrease of cerebral blood flow and that isolated mental delay in infants weighing <1,250 g is associated with the total dosage and duration of doxapram therapy.

Objectives: To evaluate the effects of doxapram on cerebral hemodynamics in preterm infants using cerebral Doppler ultrasonography and near-infrared spectroscopy.

Methods: Preterm infants who required treatment with doxapram for apnea of prematurity unresponsive to caffeine were treated with doxapram at an hourly dose of 0.5 mg x kg(-1).h(-1), followed by 1.5 and 2.5 mg x kg(-1).h(-1).

Results: 20 preterm infants were studied. Doxapram induced a significant decrease of oxygenated hemoglobin (O(2)Hb) and cerebral intravascular oxygenation (HbD = O(2)Hb - HHb) and an increase of HHb and CtOx concentrations, while cerebral blood volume and cerebral blood flow velocity did not change.

Conclusions: Doxapram infusion induces the increase of cerebral oxygen consumption and requirement and the contemporary decrease of oxygen delivery probably mediated by a decrease of cerebral blood flow. Caution must be recommended in prescribing this drug for apnea of prematurity.

In neonatal diabetes mellitus (NDM), a rare genetic disorder, insulin therapy is required but the management is difficult. Frequent blood glucose determinations are necessary in most cases. Microdialysis subcutaneous glucose monitoring (MSGM) is feasible in neonates and has been proposed to reduce painful blood sampling and blood loss. We have applied long-term MSGM to a small-for-date female newborn with transient NDM. We found a good correlation of subcutaneous and blood glucose concentration over a wide range of values. MSGM enabled a reduction in blood glucose determinations during optimization of intravenous insulin treatment and initiation of continuous subcutaneous insulin infusion. We conclude that long-term MSGM is feasible and may reduce painful blood sampling and blood loss in NDM. Furthermore, long-term MSGM may hold a potential for avoiding hypoglycemic episodes and earlier discharge.

Background: Hypoxemic episodes in ventilated preterm infants are frequently caused by reduced ventilation due to a decrease in lung volume and acute worsening of respiratory mechanics.

Objective: To compare the efficacy of conventional time-cycled, pressure-limited flow synchronized intermittent mandatory ventilation (SIMV) and volume-targeted SIMV (VT-SIMV) in reducing the frequency and severity of these episodes.

Methods: SIMV and VT-SIMV were compared in preterm infants with frequent spontaneous episodes of hypoxemia. VT-SIMV was provided with the Draeger Babylog 8000plus ventilator in volume-guarantee mode.

Results: In all, 32 infants (birth weight 668 +/- 126 g, gestational age 24.8 +/- 1.1 weeks, age 37.5 +/- 17.3 days) were studied during 2-hour periods of SIMV and VT-SIMV in random sequence. In an initial phase, a group of 12 infants was supported during VT-SIMV with a target tidal volume of 4.5 ml/kg (VT-SIMV 4.5). A planned interim analysis did not show differences in frequency and duration of hypoxemia between VT-SIMV 4.5 and SIMV, and the initial phase was stopped. In a second phase of the study, 20 infants were studied while supported with a target tidal volume of 6.0 ml/kg during VT-SIMV (VT-SIMV 6.0). In the second phase of the study, the frequency of the hypoxemic episodes did not change but the mean episode duration was shorter during VT-SIMV compared to SIMV. The proportion of mechanical breaths with small tidal volumes (< or =3 ml/kg) was reduced during VT-SIMV 6.0 versus SIMV, while the peak inspiratory pressure and mean airway pressure were increased.

Conclusion: VT-SIMV did not reduce the frequency of hypoxemic episodes, but VT-SIMV 6.0 was effective in reducing the duration of the hypoxemic episodes.

Objective: To search for recent clinical trials of neonatal surfactant treatment and report their findings.

Methods: Recent was defined as published between 2000 and 2005. An online search on PubMed was made on 30th December 2005 using the following terms: surfactant treatment, clinical trials and neonate, with limits of years 2000 to 2005 and age - newborn from birth to 1 month. Randomised clinical trials (RCTs) and systematic reviews of RCTs were prioritised and studies in children and animals were excluded from further analysis.

Results: 175 papers were found in this search. Only about half of these papers were directly related to some aspect of surfactant treatment and of these just over one-half were either RCTs or systematic reviews of RCTs. Of the 34 RCTs of surfactant treatment, 3 were excluded as they involved children or animals rather than neonates. Twenty-nine trials studied preterm babies with respiratory distress syndrome (RDS) and 2 were for meconium aspiration syndrome (MAS) in term infants. The median sample sizes of these studies were RDS (92, range 19-1,361) and MAS (42, range 22-61). Eighteen of the RDS trials compared two or more surfactant preparations, the most frequently studied being Curosurf and Survanta but altogether 11 different surfactants were compared. These new RCTs need to be analysed by meta-analyses in systematic reviews. Twelve systematic reviews were found and these demonstrated the superiority of prophylactic over selective use of surfactant in babies <30 weeks, natural over synthetic surfactant and the absence of an increase in long-term developmental sequelae. Surfactant for MAS may reduce the severity of respiratory illness and the need for extracorporeal membrane oxygenation. Of the non-randomised trials' novel delivery methods, failure to use evidence-based guidelines and the benefit of surfactant for babies <25 weeks were the most interesting.

Conclusions: Surfactant remains one of the most effective and safest interventions in neonatology. Prophylactic natural surfactant seems to be the most evidence-based treatment for babies <30 weeks. Of the newer synthetic surfactants, only Surfaxin has been compared with currently used surfactants and systematic reviews are needed to establish if it has a role in treatment of RDS. The improvement in outcome for babies <25 weeks has been due to a number of interventions: prenatal steroids, prenatal antibiotics and postnatal surfactant. Clinical trials of surfactant replacement in the neonate continue to be published with remarkable frequency.

Background: Energy failure due to insufficient cerebral O2-supply leads to excess accumulation of calcium ions in presynaptic neurons, followed by excess release of excitatory amino acids, which are potent neurotoxins, into the synaptic cleft.

Aim: To investigate whether electrocortical brain activity (ECBA) can provide an adequate measure for excitatory amino acid release due to hemorrhagic hypotension.

Methods: Ten near-term lambs were delivered at 127 days of gestation (term: 147 days). After a stabilization period, hypotension was induced by stepwise withdrawal of blood. Cerebral microdialysis was used to measure the concentrations of glutamate and aspartate.

Results: During hypotension, mean arterial blood pressure, cerebral O2-supply and ECBA decreased and the extracellular concentration of glutamate increased significantly. ECBA was significantly related to glutamate (R2: 0.67, p < 0.001) and aspartate (R2: 0.57, p < 0.001) concentrations.

Conclusion: The extracellular release of glutamate and aspartate in the cerebral cortex increases after hemorrhagic hypotension in near-term born lambs. The extracellular overflow of glutamate and aspartate were significantly inversely related to ECBA.