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Background: In an effort to mitigate the major morbidities and mortality associated with extreme prematurity, we have developed an EXTrauterine Environment for Neonatal Development (EXTEND) designed to provide physiologic support of extremely premature infants.Objectives: We have previously shown that long-term, physiologic support of premature fetal lambs is possible with EXTEND, but in this study, we sought to demonstrate bioenergetic equipoise at the tissue level.Methods: Four premature fetal lambs were delivered by hysterotomy at gestational ages (GA) of 105-107 days (term ∼145 days), cannulated via the umbilical vessels, and transitioned to support on EXTEND for 3-4 weeks. Five control fetuses were age-matched to the GA of experimental fetuses at the time of study end (128-134 days GA) and immediately sacrificed after hysterotomy. Mitochondria were isolated from the heart, liver, kidney, and skeletal muscle of fetuses at the time of sacrifice, and oxygen consumption rates (OCRs) were measured.Results: There were no differences in basal mitochondrial OCR between EXTEND and control fetuses for heart, kidney, or skeletal muscle. For liver, the basal OCR was higher in EXTEND fetuses compared to controls. There were no differences in physiologic maximal OCR or reserve capacity for any tissue analyzed.Conclusions: Fetal lambs supported by EXTEND demonstrate physiologic mitochondrial function as evidenced by adequate basal and physiologic maximal cellular respiration as well as preserved reserve capacity. [ABSTRACT FROM AUTHOR]

Introduction: We have recently developed an extra-uterine environment for neonatal development (EXTEND) capable of supporting premature fetal lambs and have been able to replicate hypoxic in utero conditions by controlling fetal oxygen delivery. In this study, we investigated the fetal mitochondrial response to hypoxia.Methods: Eight premature fetal lambs were delivered via hysterotomy and transitioned to extra-uterine support for 3 weeks. The lambs were divided into 2 groups: normoxic fetuses which maintained physiologic oxygen delivery and hypoxic fetuses in which oxygen delivery was significantly reduced. Control fetuses were delivered via hysterotomy but not cannulated. Measurements of mitochondrial membrane potential (MMP) were performed in peripheral blood mononuclear cells.Results: There were no significant differences in MMP between normoxic EXTEND fetuses and controls. Hypoxic fetuses had significantly more depolarized mitochondria compared to normoxic fetuses overall, and these changes were specifically appreciated in weeks 1 and 2, but not by week 3. Hypoxic fetuses had significantly elevated levels of HIF-1α compared to normoxic fetuses in the first 2 weeks.Discussion: Normoxic fetal lambs supported by EXTEND demonstrate normal mitochondrial function as evidenced by equivalent membrane potentials compared to control fetuses. Hypoxic fetuses exhibit mitochondrial dysfunction, though they do show evidence of adaptation after 3 weeks of hypoxic exposure. [ABSTRACT FROM AUTHOR]

Introduction: The presence of CHD in the fetus is associated with perturbations of brain growth and maturation, but the underlying mechanisms remain controversial. We tested the hypothesis that chronic fetal hypoxia, at a severity present in many types of CHD, would lead to abnormal neurodevelopment. Methods: Eight fetal sheep were cannulated onto a pumpless extracorporeal oxygenator via the umbilical vessels and supported in a fluid filled environment under normoxic or hypoxic conditions. Total parenteral nutrition was provided. Age-matched control fetuses were harvested for comparison. At necropsy, brains were weighed and fixed for histopathology. Neurons were quantified in white matter (WM) tracts and the thickness of the external granular layer of the cerebellum was measured to assess neuronal migration. WM capillary density was quantified. Myelination was assessed using a WM integrity scale. Data was analyzed with unpaired Student's t tests or one-way ANOVA, as appropriate. Results: Study duration was the same between the hypoxic and normoxic groups (Table). Oxygen delivery was reduced in hypoxic fetuses, but umbilical blood flow and caloric delivery were not different between groups. Compared to control animals, hypoxic fetuses had reduced brain size. Hypoxic fetuses had reduced neuronal density and increased external granular layer thickness, consistent with delayed neuronal migration. In hypoxic fetuses, capillary density was increased in WM. Cortical myelin integrity score was lower in the hypoxic group. There was a significant negative correlation between the myelin integrity score and capillary density (r =-0.71, p<0.01). Conclusions: Chronic fetal hypoxia leads to reduced brain size, WM hyper-vascularity, decreased neuronal migration, and impaired myelination, similar to the neuropathological findings observed in children born with CHD. These findings support the hypothesis that fetal hypoxia, even in the setting of normal substrate delivery, impairs neurodevelopment. [ABSTRACT FROM AUTHOR]

Objectives: The objective of this study was to investigate changes in serum biomarkers of acute brain injury, including white matter and astrocyte injury during chronic foetal hypoxaemia. We have previously shown histopathological changes in myelination and neuronal density in fetuses with chronic foetal hypoxaemia at a level consistent with CHD., Methods: Mid-gestation foetal sheep (110 ± 3 days gestation) were cannulated and attached to a pumpless, low-resistance oxygenator circuit, and incubated in a sterile fluid environment mimicking the intrauterine environment. Fetuses were maintained with an oxygen delivery of 20-25 ml/kg/min (normoxemia) or 14-16 ml/kg/min (hypoxaemia). Myelin Basic Protein and Glial Fibrillary Acidic Protein serum levels in the two groups were assessed by ELISA at baseline and at 7, 14, and 21 days of support., Results: Based on overlapping 95% confidence intervals, there were no statistically significant differences in either Myelin Basic Protein or Glial Fibrillary Acidic Protein serum levels between the normoxemic and hypoxemic groups, at any time point. No statistically significant correlations were observed between oxygen delivery and levels of Myelin Basic Protein and Glial Fibrillary Acidic Protein., Conclusion: Chronic foetal hypoxaemia during mid-gestation is not associated with elevated serum levels of acute white matter (Myelin Basic Protein) or astrocyte injury (Glial Fibrillary Acidic Protein), in this model. In conjunction with our previously reported findings, our data support the hypothesis that the brain dysmaturity with impaired myelination found in fetuses with chronic hypoxaemia is caused by disruption of normal developmental pathways rather than by direct cellular injury.