White matter apoptosis is increased by delayed hypothermia and rewarming in a neonatal piglet model of hypoxic ischemic encephalopathy

Abstract

Therapeutic hypothermia is widely used to treat neonatal hypoxic ischemic (HI) brain injuries. However, potentially deleterious effects of delaying the induction of hypothermia and of rewarming on white matter injury remain unclear. We used a piglet model of HI to assess the effects of delayed hypothermia and rewarming on white matter apoptosis. Piglets underwent HI injury or sham surgery followed by normothermic or hypothermic recovery at 2 h. Hypothermic groups were divided into those with no rewarming, slow rewarming at 0.5°C/h, or rapid rewarming at 4°C/h. Apoptotic cells in the subcortical white matter of the motor gyrus, corpus callosum, lateral olfactory tract, and internal capsule at 29 h were identified morphologically and counted by hematoxylin & eosin staining. Cell death was verified by TUNEL assay. White matter neurons were also counted, and apoptotic cells were immunophenotyped with the oligodendrocyte marker 2′,3′-cyclic-nucleotide 3′-phosphodiesterase (CNPase). Hypothermia, slow rewarming, and rapid rewarming increased apoptosis in the subcortical white matter relative to normothermia (p<0.05). The number of white matter neurons was not lower in groups with more apoptosis after hypothermia or rapid rewarming, indicating that the apoptosis occurred among glial cells. Hypothermic piglets had more apoptosis in the lateral olfactory tract than those that were rewarmed (p<0.05). The promotion of apoptosis by hypothermia and rewarming in these regions was independent of HI. In the corpus callosum, HI piglets had more apoptosis than shams after normothermia, slow rewarming, and rapid rewarming (p<0.05). Many apoptotic cells were myelinating oligodendrocytes identified by CNPase positivity. Our results indicate that delaying the induction of hypothermia and rewarming are associated with white matter apoptosis in a piglet model of HI; in some regions these temperature effects are independent of HI. Vulnerable cells include myelinating oligodendrocytes. This study identifies a deleterious effect of therapeutic hypothermia in the developing brain.

Recent Information on the Pathogenesis and Treatment of Hypoxic-Ischemic Brain Lesions in Newborns

“…Гипотермия (переохлаждение) снижает образо-вание свободных радикалов и уровень глутамата, умень-шает потребность в кислороде и уменьшает апоптоз [4,78,79]; одним из ведущих механизмов терапевтиче-ского эффекта считается противовоспалительный [80]. Основные эффекты гипотермии направлены на действие в период «окна возможностей», или латентного пери-ода энергетической недостаточности [6], который, как говорилось выше, предположительно длится с 30 мин после рождения до 24-48 ч. Именно в этот период появляется возможность не допустить или минимизиро-вать вторичную фазу энергетической недостаточности.…”

Hypothermia and Rewarming Activate a Macroglial Unfolded Protein Response Independent of Hypoxic-Ischemic Brain Injury in Neonatal Piglets

“…[1] However, approximately half of survivors have persistent neurodevelopmental disabilities despite receiving hypothermia. [1, 2] We theorize that adverse effects from delaying the induction of hypothermia [3] and rewarming [4, 5] may be partially responsible for these neurologic impairments. We previously demonstrated that rewarming increases cortical neuronal apoptosis and caspase-3 cleavage after hypoxia-ischemia (HI) in a piglet model.…”

“…[4] Hypothermia and rewarming also promote glial apoptosis in the white matter, an effect that may be independent of HI in some brain regions. [5] Cortical and white matter injuries on MRI predict neurodevelopmental and motor impairments in survivors of HIE. [6, 7] Thus, there is need to define the mechanisms through which apoptotic cascades are activated after HI, hypothermia, and rewarming; to clarify targets for adjuvant therapies; and to minimize off-target effects from hypothermia and rewarming.…”

“…[4, 5, 8-10] These events can be upstream signals for cell death. Endoplasmic reticulum (ER) stress is involved in the cellular heat-shock response [11] and may also mediate cellular injury during hypothermia and rewarming.…”

The search continues: neuroprotection for all neonates with hypoxic-ischemic encephalopathy

“…Brain injury biomarkers, such as circulating blood-based analytes (14,15) or physiologic measures of autonomic dysfunction (16,17), might be able to identify neonates at greatest risk of severe brain injury and provide real-time feedback on treatment efficacy. Optimizing cerebrovascular blood pressure autoregulation (18)(19)(20) with individualized hemodynamic goals and avoiding hypocapnia (21) might also improve outcomes. Moreover, current intrapartum fetal monitoring techniques do not sufficiently identify babies at risk of intrapartum hypoxia.…”