Intra-ischemia vs post-ischemia hypothermia induced neurological and cardiac protection via the up-regulation of RBM3

Introduction: Therapeutic hypothermia is an established protective strategy in patients suffering from cardiac arrest involving global ischemia. However, the optimal timing and underlying mechanisms remains to be elucidated.

Objective: This study aimed to compare the cardio/neuroprotective effect of mild hypothermia (33.5°C) at different times of ischemia: intra and post-ischemia.

Methods: A monoculture of murine HL-1 cardiomyocytes and a direct co-culture of murine hippocampal HT-22 neuronal and BV-2 microglial cells were used to investigate the cardio/neuro-protective effects of hypothermia, respectively. Ischemic insult was induced for 6 h at 0.2% O2 in a glucose/serum free medium. After ischemia, nutrients and oxygen was restored to the cells to simulate reperfusion. Intra-ischemia and post-ischemia cooling to 33.5°C was maintained for 24h. Cell death was determined by LDH and cTNT release. Changes in cell morphology were analyzed via light microscopy. Cold shock protein RBM3 expression was quantified by Western blotting.

Results: Ischemia/reperfusion injury resulted in increased cell death as seen in significantly higher LDH and cTNT releases compared to normoxic controls. Intra-ischemic cooling was superior to post-ischemic cooling at global protection of both the cardiomyocytes and neuronals/microglials. Additionally, a corresponding up-regulation of RBM3 expression by hypothermia was observed in both culture models.

Conclusions: Hypothemia is an effective intervention to protect the heart and brain from tissue loss due to ischemia/reperfusion injury, possibly through the up-regulation of cold shock protein RBM3.