Mild hypothermic cross adaptation resists hypoxic injury in hearts: a brief review

Severe cardiac hypoxia is responsible for significant morbidity and mortality in an emergency setting. Most cardiac hypoxia relates to ischemia and surgical events. Although the ischemic mortality rate and the risks of cardiac surgery have significantly decreased in past decades, myocardial protection still plays a major role in survival of hypoxic injury. Cross adaptation as a physiological regulation for homeostasis can resist injury caused by harmful environmental effects and diseases, including hypothermic adaptation. Treatment with hypothermia has been used for fifty years as a protective mechanism to avoid hypoxic injury. Since cold temperatures can cause damage, it is important to gather physiological data to distinguish protective from injurious temperatures. Although results of temperature trials in clinical practice vary, a critical temperature to resist hypoxic/ischemic injury in heart was found to be around 30 degrees C, suggesting a hypothermia protective threshold. Pretreatment with mild hypothermia can resist subsequent hypoxia/ischemia, implying involvement of cross adaptation in protection. Safeguard hypothermia can directly reduce the build up of harmful metabolites and energy demand in hypoxic tissues, as well as preserve mitochondrial membrane specific proteins beta subunit of F1-ATPase and adenine nucleotide translocase isoform 1. Mechanisms of preservation include inactivation of the p53 related pathways, representing anti-apoptosis, and modification of the mRNA level of succinodehydrogenease, indicating a beneficial effect on the aerobic pathway. Stress proteins are also induced. Resultant cellular adaptations serve to maintain myocardial integrity and improve functional recovery during reoxygenation or reperfusion.