Moderate hypothermia initiated during oxygen-glucose deprivation preserves HL-1 cardiomyocytes

Objectives: Therapeutic hypothermia (TH) is an acknowledged strategy for neuroprotection for patients suffering from hypoxic-anoxic brain injury (HAI). Albeit similar pathomechanisms of HAI for both brain and heart, moderate TH (32-34°C) has not been established as a heart-protective measure. Therefore, we investigated the cardioprotective effects of moderate TH on oxygen-glucose deprivation/re-oxygenation (OGD/R)-induced injury in HL-1 cardiomyocytes.

Methods: Cardiac OGD/R injury was induced by exposing HL-1 cardiomyocytes to 0.2% oxygen in serum/glucose-free medium for 6h. OGD injured cells were subsequently re-oxygenated with 21% oxygen in complete medium. Two hypothermic protocols were investigated: Post-OGD cooling to 33.5°C for 24 h initiated at the start of re-oxygenation and intra-OGD cooling to 33.5°C for 24 h initiated after 3 h of OGD and maintained throughout the re-oxygenation phase. Cell viability was determined by LDH and cTnT releases. Mitochondria dysfunction was evaluated by intracellular ATP content and cellular metabolic activity was accessed by MTT reduction. Activation of caspase 3 was analyzed by Western blot.

Results: OGD/R-induced injury resulted in increased cell death (higher LDH and cTnT releases), mitochondrial impairment (decreased ATP content), and decreased cellular metabolic activity (decreased MTT reduction). Only intra-OGD cooling attenuated both OGD and OGD-R-induced injuries (significantly decreased LDH and cTnT releases and increased ATP contents and MTT reduction). Furthermore, caspase 3 activation was abated by intra-OGD cooling. No protective effects were observed by post-OGD cooling.

Conclusions: Moderate TH initiated during OGD is a promising intervention for the protection of cardiomyocytes from OGD/R-induced injury. The attenuation of mitochondrial dysfunction and apoptosis by intra-OGD cooling are beneficial effects of hypothermia-induced cardioprotection, resulting in minimized myocardial cell death after OGD and OGD-R-induced injuries.