Myocardial protection by acidic amino acids and natural dipeptides: potential for an underused resource

Stopping then restarting the blood flow to the heart can cause ischaemia reperfusion (IR) injury. This can happen during revascularisation following a myocardial infarction and during on pump cardiac surgery using cardioplegic arrest. Despite extensive studies to identify cardioprotective interventions, the myocardium continues to sustain significant injury. Therefore, there is a need to identify agents that can be used during IR. This review focuses on the potential cardioprotective role for acidic amino acids and natural dipeptides using evidence from experimental studies and clinical trials with particular emphasis on their membrane transport. Acidic amino acids are present at high concentration in the heart with a large tissue to plasma concentration gradient, where they are involved in protein synthesis and intermediary metabolism. During cardiac insults they are lost from heart cells but replenishment leads to cardioprotection through energy provision, protection against the production of reactive oxygen species production and improved calcium homeostasis. One important determinant of the intracellular concentration of acidic amino acids and natural dipeptides is membrane transport. The expression and activity of the acidic amino acids transporters EAAT1-3 and the dipeptide transporter, PEPT2 have been demonstrated in membrane vesicles and isolated cardiomyocytes. Improvements in our understanding of these different transport mechanisms should lead to the maximisation of acidic amino acid and natural dipeptide uptake during IR leading to improved cardioprotection.