Nutritional supplementation with mixed essential amino acids enhances myocyte survival, preserving mitochondrial functional capacity during ischemia-reperfusion injury

In patients undergoing coronary surgery, the uptake of amino acids, which has been shown to correlate with oxygen consumption, is a mechanism of cardiac adaptation to the iatrogenic ischemia-reperfusion injury associated with cardioplegic arrest. Based on these premises, we sought to determine whether oral supplementation with mixed amino acids may protect the rat heart exposed to ischemia-reperfusion and to address whether this hypothesized cardioprotection is achieved, at least in part, through preservation of the energy-producing properties of mitochondria. Sprague–Dawley rats were fed (by enteral route) a liquid diet, with or without mixed essential amino acids (daily dose of 1 g/kg) for 30 days. Hearts from anesthetized rats were perfused by the Langendorff method and randomized to 3 groups. The control group was perfused with buffer for 60 minutes; the ischemia-reperfusion control and the amino acid–treated groups were exposed to 35 minutes of ischemia, followed by 60 or 120 minutes of reperfusion. Amino acid supplements minimized infarct size (22 ± 1.8% vs 33 ± 2.5%; p <0.05) and occurrence of cardiomyocyte apoptosis, as assessed by co-localization of terminal deoxynucleotidyl transferase–mediated dUTP nick end labeling (TUNEL) and caspase-3–positive staining (p <0.01). Long-term treatment with amino acids also reduced the proportion of cardiomyocytes exhibiting immunostaining for cleaved caspase-9 (p <0.01) but was ineffective on processing of caspase-8. Similar results were obtained in the whole heart by caspase activity assays (p <0.01). The lessened activation of caspase-9 detected in amino acid-treated hearts paralleled a strong reduction in mitochondrial release of cytochrome c. Adenosine triphosphate (ATP) content and rate of ATP production in isolated mitochondria were reduced by >75% in control hearts after 2 hours of reperfusion (p <0.05 vs control hearts); these values returned toward those of the control group in hearts supplemented with amino acids (p <0.01). Finally, the oxygen consumption rate in myocardial skinned bundles was markedly reduced in ischemia-reperfusion control hearts and almost normalized in amino acid-treated hearts (approximately 20% and 93% of the value for normoxic hearts; p <0.01). These results suggest that oral amino acid supplementation attenuates the extent of ischemia-reperfusion injury in the rat heart, through preservation of the mitochondria-generated production of high-energy phosphates.