Effects Of Mild Hypothermia On Expression Of Nrf2and HO-1in Cerebral Cortex And Hippocampus After Cardiac Arrest And Cardiopulmonary Resuscitation In Rats

Objectives:1. To observe the effects of mild hypothermia on expression of Nrf2and HO-1incerebral cortex and hippocampus after CPR in SD rats and further explore the possiblemechanism of action;2. To explore the optimal time of mild hypothermia for brain protection.Methods:To copy an asphyxia CA model,40SD rats were randomly divided into controlgroup (n=4) and model group (n=36). Model group is divided into the normothermiagroup (n=12) and mild hypothermia group (n=24), mild hypothermia group then dividedinto two groups: mild hypothermia before ROSC group (n=12) and mild hypothermiaafter ROSC group (n=12). Body temperature in normothermia group was maintained at37.5～39℃, while hypothermia group maintained at32～34℃by surface cooling withthe ice pack. Each model group then divided into three groups:15min,30min,60minafter ROSC. Reverse transcriptase polymerase chain reaction was performed to detectthe expression of Nrf2and HO-1mRNA in cerebral cortex and hippocampus. HEstaining was performed to observe histological changes. Immunohistochemistry wasperformed to detect the expression of Nrf2and HO-1protein expression. Results:1. Changes in morphology observed by hematoxylin-eosin staining1) Compare to control group, the normal neurons in hippocampus was significantlyreduced in model group and neuron shrinkage, cell body smaller, nucleus condensation,the nucleolus disappears, the cell of various shapes, coloring dark, neurons and glialcells around the gap widened;2) Compare to normothermia group, pathological structure have significantlyimproved in mild hypothermia group: hippocampus neurons arranged closely, clearstructure, neuron structure is more complete, neurons and glial cells around the gapwidened extent reduced, The nuclei of nerve cells pyknosis were not evident, nosignificant degeneration and atrophy;3) Compare to mild hypothermia before ROSC group, there are no significant changesin pathological patterns in mild hypothermia after ROSC group, two group have similarpathological patterns.2. Expression of Nrf2and HO-1mRNA observed by RT-PCR1) The expression of Nrf2and HO-1mRNA was a statistically significant differencebetween control and each model group(P<0.05, respectively), expression in modelgroup is higher than that in control group;2) The expression of Nrf2and HO-1mRNA in15min,30min,60min afte ROSCgroups are higher than that in the control group;3) The expression of Nrf2and HO-1mRNA was a statistically significant differencebetween normothermia group and mild hypothermia group(P<0.05), expression in mildhypothermia is higher than that in normothermia group;4) The expression of Nrf2and HO-1mRNA was no significant difference(P>0.05)between mild hypothermia before ROSC group and mild hypothermia afterROSC group; 5) The expression of Nrf2and HO-1mRNA was no significant difference (P>0.05)atthree time points of15min,30min,60min after ROSC.3. Expression of Nrf2and HO-1protein observed by IHC1) The expression of Nrf2and HO-1protein was a statistically significant differencebetween control and each model group(P<0.05, respectively), expression in modelgroup is higher than that in control group;2) The expression of Nrf2and HO-1protein in15min,30min,60min afte ROSCgroups are higher than that in the control group;3) The expression of Nrf2and HO-1protein was a statistically significant differencebetween normothermia group and mild hypothermia group(P<0.05), expression in mildhypothermia is higher than that in normothermia group;4) The expression of Nrf2and HO-1protein was no significant difference(P>0.05)between mild hypothermia before ROSC group and mild hypothermia afterROSC group;5) The expression of Nrf2and HO-1protein was no significant difference (P>0.05)atthree time points of15min,30min,60min after ROSC.Conclusions:1. The expression of Nrf2and HO-1in cerebral cortex and hippocampus after CPRincreased in early stage, the expression of Nrf2and HO-1has increased at15min,30min,60min after ROSC;2. Mild hypothermia in CPR has significantly improved the pathological structure ofthe cerebral cortex and hippocampus: hippocampus neurons arranged closely, clearstructure, neuron structure is more complete, neurons and glial cells around the gapwidened extent reduced, The nuclei of nerve cells pyknosis were not evident, nosignificant degeneration and atrophy; 3. Mild hypothermia has increased expression of Nrf2and HO-1m RNA and proteinin cerebral cortex and hippocampus;4. The possible mechanism of mild hypothermia for neuroprotection is to activateNrf2-ARE signaling pathway than increase the expression of Nrf2and its downstreamgene HO-1.