L-lactic acid induces short- and long-term cardioprotective effects through MCT1 transport, induction of metabolic reprogramming, and gene expression modulation.

Lactic acid is recognized as an alternative fuel source for various tissues and is acknowledged for its protective effects in the brain. However, its potential as a cardioprotective agent remains controversial. Here, we aimed to (1) evaluate the impact of acute L-lactic acid administration, given at the onset of reperfusion, on myocardial infarct size in isolated mouse hearts submitted to transient global ischemia, (2) assess the effects of chronic L-lactic acid exposure in living myocardial slices (LMS) from human hearts, and (3) elucidate the underlying mechanisms. Isolated mouse hearts were submitted to global ischaemia (35 min) followed by reperfusion (60 min), with L-lactic acid being or not administered during the first 15 min of reperfusion. L-lactic acid reduced infarct size by 23% at 20 mmol/L. An acidic Krebs induced less protection, and monocarboxylate transporter 1 (MCT1) inhibition with AR-C 141990 attenuated L-lactic acids protection to the level of acidic Krebs. 1H NMR spectroscopy revealed significant metabolic changes in L-lactic acid-treated hearts, with pathway enrichment analysis showing a nearly a 3-fold enrichment in pyruvate metabolism, fatty acid biosynthesis, and gluconeogenesis, suggesting a metabolic shift. Moreover, electrically stimulated human LMS treated with L-lactic acid for 48 h exhibited improved contractility and upregulation of structural and functional cardiomyocyte components, stemness-related markers, and pro-angiogenic proteins. These findings support a cardioprotective role for L-lactic acid in both short- and long-term contexts, mediated in part by its uptake through the MCT1 transporter, induction of metabolic reprogramming, and gene expression modulation.