Introduction: Current hypothermia protocols for term infants with hypoxic-ischemic encephalopathy provide partial white matter protection. In experimental models, recombinant erythropoietin (rEpo) offers partial protection from white matter injury after hypoxia-ischemia, but it is unclear whether adding rEpo therapy to hypothermia can further improve white matter outcomes.
Methods: Term-equivalent (0.85 gestation) fetal sheep received 30 min of global cerebral ischemia, then from 3 to 72 hours after ischemia, either normothermia plus vehicle (ischemia-control, n=8), cerebral hypothermia (ischemia-hypo, n=8), rEpo infusion (ischemia-rEpo, 5000 IU/kg loading dose, then 5000 IU/kg every 6 hours, n=8), or co-treatment with hypothermia plus rEpo (ischemia-rEpo-hypo, n=8). Sheep were killed 7 days after ischemia.
Results: Cerebral ischemia was associated with loss of total (Olig2-positive) oligodendrocytes in the intragyral and periventricular white matter (p<0.05), with reduced area fraction of myelin basic protein (MBP, p<0.05) and immature-to-mature (CNPase) oligodendrocytes (p<0.05). Ki67-positive cell proliferation was increased in both regions (p<0.05). Hypothermia attenuated loss of Olig2 (p<0.05) in the intragyral and periventricular white matter tracts and improved MBP-area fraction (p<0.05) in the intragyral white matter after hypoxia-ischemia. rEpo did not improve Olig2 survival and had an intermediate effect on MBP. Hypothermia plus rEpo improved CNPase-area fraction in the intragyral white matter (p<0.05) compared with each intervention alone, but did not improve Olig2 or MBP, compared to hypothermia alone. Both hypothermia and hypothermia plus rEpo, but not rEpo, suppressed Ki67-positive cell proliferation in both white matter regions (p<0.05).
Conclusion: These preliminary findings suggest that a standard protocol of cerebral hypothermia provides greater white matter protection after ischemia in near-term fetal sheep than high-dose rEpo infusion. Although combined treatment increased survival of immature and mature oligodendrocytes compared to either alone, it did not further improve overall protection of myelination, and did not prevent hypothermic suppression of cell proliferation.