Long-Term Neuropathological Changes Associated with Cerebral Palsy in a Nonhuman Primate Model of Hypoxic-Ischemic Encephalopathy

Abstract

Background: Cerebral palsy (CP) is the most common motor disability in childhood, with a worldwide prevalence of 1.5-4/1,000 live births. Hypoxic-ischemic encephalopathy (HIE) contributes to the burden of CP, but the long-term neuropathological findings of this association remain limited. Methodology: Thirty-four term Macaca nemestrina macaques were included in this long-term neuropathological study: 9 control animals delivered by cesarean section and 25 animals with perinatal asphyxia delivered by cesarean section after 15-18 min of umbilical cord occlusion (UCO). UCO animals were randomized to saline (n = 11), therapeutic hypothermia (TH; n = 6), or TH + erythropoietin (Epo; n = 8). Epo was given on days 1, 2, 3, and 7. Animals had serial developmental assessments and underwent magnetic resonance imaging with diffusion tensor imaging at 9 months of age followed by necropsy. Histology and immunohistochemical (IHC) staining of brain and brainstem sections were performed. Results: All UCO animals demonstrated and met the standard diagnostic criteria for human neonates with moderate-to-severe HIE. Four animals developed moderate-to-severe CP (3 UCO and 1 UCO + TH), 9 had mild CP (2 UCO, 3 UCO + TH, 3 UCO + TH + Epo, and 1 control), and 2 UCO animals died. None of the animals treated with TH + Epo died, had moderate-to-severe CP, or demonstrated signs of long-term neuropathological toxicity. Compared to animals grouped together as having no CP (no-CP; controls and mild CP only), animals with CP (moderate and severe) demonstrated decreased fractional anisotropy of multiple white-matter tracts including the corpus callosum and internal capsule, when using Tract-Based Spatial Statistics (TBSS). Animals with CP had decreased staining for cortical neurons and increased brainstem glial scarring compared to animals without CP. The cerebellar cell density of the internal granular layer and white matter was decreased in CP animals compared to that in control animals without CP. Conclusions/Significance: In this nonhuman primate HIE model, animals treated with TH + Epo had less brain pathology noted on TBSS and IHC staining, which supports the long-term safety of TH + Epo in the setting of HIE. Animals that developed CP showed white-matter changes noted on TBSS, subtle histopathological changes in both the white and gray matter, and brainstem injury that correlated with CP severity. This HIE model may lend itself to further study of the relationship between brainstem injury and CP.

Perinatal hypoxic-ischemic brain injury in large animal models: Relevance to human neonatal encephalopathy

“…In monkeys, complete asphyxia with sustained loss of arterial pressure produces neurologic abnormalities symptoms of cerebral palsy with preferential injury to somatosensory, auditory, and vestibular nuclei in brainstem, thalamus, and cerebellum. 22,23,189 In models of partial asphyxia in fetal monkeys, fetal sheep, and newborn piglets, preferential injury is produced in primary somatosensory and motor cortices, basal ganglia, and thalamus. 43,79,102,122,168 Although both patterns of injury are reported in human autopsy tissue and MRI, the pattern seen with partial asphyxia is more frequent.…”

“…When pooling monkeys with moderate or severe neurologic deficit versus those with mild or no neurologic deficit among groups, fractional anisotropy in internal capsule and corpus callosum and cerebellar cell density and white matter were decreased in those with moderate or severe neurologic impairment. 189 These results in monkeys, together with earlier work in rodents, led to a Phase II clinical trial of high-dose erythropoietin as an adjunct therapy with hypothermia. 201 Effects on diffusion-weighted lesion volumes at 12 months are encouraging, 202 and a large scale Phase III trial is underway.…”

“…32,51 Whereas hypothermia affords some protection of white matter, such as in the posterior limb of the internal capsule, 185 white matter injury persists in term HIE neonates. [186][187][188] Persistent white matter injury has also been seen in term monkey fetuses subjected to complete asphyxia 189 and in newborn piglets subjected to hypoxia-asphyxia. 190 In piglets with a 2-h delay in hypothermia, increases in apoptotic cells, thought to be mainly mature oligodendrocytes, were seen in multiple white matter regions not only after rewarming, but also during hypothermia relative to that seen with normothermic recovery from HI.…”

Treatment of Neonatal Hypoxic-Ischemic Encephalopathy with Erythropoietin Alone, and Erythropoietin Combined with Hypothermia: History, Current Status, and Future Research

“…In a follow-on study in 2017 by McAdams et al [108], the same groups and treatment regimes as Traudt et al [107] were used. None of the animals treated with combined HT and EPO demonstrated signs of long-term neuropathological toxicity at 9 months-of-age.…”

Glial cell responses in a murine multifactorial perinatal brain injury model

“…Research efforts examining perinatal brain injury in animal models to assess cellular and molecular mechanisms of injury with the objective of devising therapies that lead to brain repair and regeneration are expanding (Titomanlio et al, 2015; Yager, 2015). Animal models focusing on perinatal asphyxia, hypoxia-ischemia, placental insufficiency, intracerebral hemorrhage, and gestational inflammation have been reported in several species (ferret, rabbit, rat, sheep, pig, primate) (McAdams et al, 2017; Yager, 2015). Although 50% of CP cases occur in normal weight babies and 10% are related to early postnatal infection, accidental brain injury, and/or drowning (Sewell et al, 2014; Titomanlio et al, 2015), no neonatal traumatic injury model has been developed reflecting these etiologies.…”