Objective: Therapeutic Hypothermia (TH) has been shown to convey neuroprotection against ischemic-reperfusion
injury. Although moderate TH (32–34°C) is a recommended treatment for adults after
out-of-hospital cardiac arrest, it is not a standard of care for children. Additionally,
the cardioprotective effect of TH after myocardial ischemia remains to be elucidated.
Therefore, the aim of our study is to investigate the effect of intra-ischemic moderate
hypothermia (33.5°C) on both a mouse atrial cardiomyocyte tumor cell line and neonatal
primary cardiomyocytes.
Methods: We established an in vitro model using mouse atrial HL-1 and primary cardiomyocytes
isolated from P1 mice to simulate myocardial ischemia with a dynamic intra-ischemic
hypothermia protocol. Cells were deprived of oxygen and glucose (OGD) for 6 hours
in glucose/serum-free starvation medium at 0.2% O2. Intraischemic cooling was initiated after 1 to 3 hours of ischemia. Cell viability
was accessed by LDH and cTnT releases. Cellular metabolic activity was analyzed using
a resazurin-base assay and intracellular ATP content was used to determine mitochondria
activity.
Results: We previously showed intra-ischemic TH initiated after 3 hours OGD conferred cardioprotection
in the HL-1 cardiomyocytes as observed in lower LDH and cTnT releases and restored
ATP content. Interestingly, the same time-temperature protocol did not convey protection
in the primary cardiomyocytes. However, we observed a protective effect in the primary
cardiomyocytes when intra-ischemic cooling was initiated earlier after 1 hour OGD.
Conclusion: As expected, primary cardiomyocytes reacted differently to intra-ischemic cooling
than the HL-1 cell line. Earlier initiation of intra-ischemic TH was required to protect
the primary cardiomyocytes from OGD-induced injury as compared with the immortalized
cell line. Since primary cells mimic better the physiological conditions, early initiation
of TH is crucial to achieving maximal cardioprotection against myocardial ischemia.
