Worldwide,
hypoxic-ischemic encephalopathy (HIE) is a major cause of neonatal mortality and morbidity. To better understand the mechanisms contributing to
brain injury and improve outcomes in neonates with HIE, better preclinical animal models that mimic the clinical situation following birth
asphyxia in term newborns are needed. In an effort to achieve this goal, we modified our nonhuman primate model of HIE induced by in utero umbilical cord occlusion (UCO) to include postnatal hypoxic episodes, in order to simulate apneic events in human neonates with HIE. We describe a cohort of 4 near-term fetal Macaca nemestrina that underwent 18 min of in utero UCO, followed by
cesarean section delivery,
resuscitation, and subsequent postnatal
mechanical ventilation, with exposure to intermittent daily
hypoxia (3 min, 8% O2 3-8 times daily for 3 days). After delivery, all animals demonstrated severe
metabolic acidosis (pH 7 ± 0.12; mean ± SD) and low APGAR scores (<5
at 10 min of age). Three of 4 animals had both electrographic and clinical
seizures. Serial blood samples were collected and plasma metabolites were determined by 2-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS). The 4 UCO animals and a single nonasphyxiated animal (delivered by
cesarean section but without exposure to UCO or prolonged sedation) underwent brain magnetic resonance imaging (MRI) on day 8 of life. Thalamic injury was present on MRI in 3 UCO animals, but not in the control animal. Following necropsy on day 8, brain histopathology revealed neuronal injury/loss and
gliosis in portions of the ventrolateral thalamus in all 4 UCO, with 2 animals also demonstrating putamen/globus pallidus involvement. In addition, all 4 UCO animals demonstrated brain stem
gliosis, with neuronal loss present in the midbrain, pons, and lateral medulla in 3 of 4 animals. Transmission electron microscopy imaging of the brain tissues was performed, which demonstrated ultrastructural white matter abnormalities, characterized by perinuclear vacuolation and axonal dilation, in 3 of 4 animals. Immunolabeling of Nogo-A, a negative regulator of neuronal growth, was not increased in the injured brains compared to 2 control animals. Using GC × GC-TOFMS, we identified metabolites previously recognized as potential
biomarkers of perinatal
asphyxia. The basal ganglia-thalamus-brain stem injury produced by UCO is consistent with the deep nuclear/brainstem injury pattern seen in human neonates after severe, abrupt hypoxic-ischemic insults. The UCO model permits timely detection of
biomarkers associated with specific patterns of neonatal
brain injury, and it may ultimately be useful for validating therapeutic strategies to treat neonatal HIE.