Effects of therapeutic hypothermia on white matter injury from murine neonatal hypoxia–ischemia

Abstract

BackgroundTherapeutic hypothermia (TH) is the standard of care for neonates with hypoxic-ischemic encephalopathy but is not fully protective in the clinical setting. Hypoxia-ischemia (HI) may cause white matter injury (WMI), leading to neurological and cognitive dysfunction.MethodsP9 mice were subjected to HI as previously described. Pups underwent 3.5 hours of systemic hypothermia or normothermia. Cresyl violet and Perl’s iron stain for histopathological scoring of brain sections was completed blindly on all brains. Immunocytochemical (ICC) staining for myelin basic protein (MBP), microglia (Iba1), and astrocytes (GFAP) was performed on adjacent sections. Volumetric measurements of MBP coverage were used for quantitative analysis of white matter.ResultsTH provided neuroprotection by injury scoring for the entire group (n=44) (p<0.0002). ICC analysis of a subset of brains showed that the lateral caudate was protected from WMI (p<0.05). Analysis revealed decreased GFAP and Iba1 staining in hippocampal regions, mostly CA2/CA3. GFAP and Iba1directly correlated with injury scores of normothermic brains.ConclusionsTH reduced injury and qualitative data suggest that hippocampus and lateral caudate are protected from HI. Mildly injured brains may better show the benefits of TH. Overall these data indicate regional differences in WMI susceptibility and inflammation in a P9 murine HI model.

Cuprizone Affects Hypothermia-Induced Neuroprotection and Enhanced Neuroblast Differentiation in the Gerbil Hippocampus after Ischemia

“…Hypothermia treatment significantly reduced the ischemia-induced reactive astrocytosis and microgliosis in the hippocampal CA1 region, but GFAP and Iba-1 immunoreactivity was significantly increased in the hippocampal CA1 region compared to the CTL group. This result is consistent with a previous study demonstrating that therapeutic hypothermia significantly decreased the intensity of GFAP and Iba-1 staining in hippocampal CA2/CA3 regions in correlation with a reduced injury score [43]. Mild hypothermia in global cerebral ischemia has been shown to decrease microglial activation and translocation of nuclear factor-kappa B [44].…”

“…This result suggests that cuprizone facilitates the demyelination induced by ischemia, and that hypothermia attenuates the demyelination induced by ischemia and/or cuprizone. Furthermore, MBP staining also suggests that hypothermia increases white matter integrity in mice after inducing the hypoxia-ischemia model [43] and after middle cerebral artery occlusion [56].…”

Residual brain injury after early discontinuation of cooling therapy in mild neonatal encephalopathy

“…For example, perinatal asphyxia without encephalopathy leads to a reduction in IQ compared with healthy peers, and mild, moderate and severe encephalopathy results in increasing severity of long-term adverse outcomes. Hypothermia is reported to have a marked neuroprotective effect in a recently described preclinical model of mild encephalopathy, where the predominant injury was in the white matter 11. Preclinical studies also report that brain cooling in the absence of perinatal asphyxia may increase apoptosis 12…”

Therapeutic hypothermia for mild neonatal encephalopathy: a systematic review and meta-analysis

“…There are concerns with such practices, as the cessation of cooling therapy prior to 24 hours following an apparent clinical recovery may be associated with residual brain injury and adverse outcomes 2. Furthermore, cooling therapy in the absence of NE may induce apoptosis 3. In contrast to the systematic review of cooling in mild NE reported by Conway et al , our review includes additional published studies, as well as raw data provided by the study authors 4…”