Cardioprotective Effect of Intraischemic Therapeutic Hypothermia in Primary Cardiomyocytes

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.