The Na+/Ca2+ exchange inhibitor SEA0400 limits intracellular Ca2+ accumulation and improves recovery of ventricular function when added to cardioplegia

Hyperkalemic or Low Potassium Cardioplegia Protects against Reduction of Energy Metabolism by Oxidative Stress

Open-heart surgery is often an unavoidable option for the treatment of cardiovascular disease and prevention of cardiomyopathy. Cardiopulmonary bypass surgery requires manipulating cardiac contractile function via the perfusion of a cardioplegic solution. Procedure-associated ischemia and reperfusion (I/R) injury, a major source of oxidative stress, affects postoperative cardiac performance and long-term outcomes. Using large-scale liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based metabolomics, we addressed whether cardioplegic solutions affect the baseline cellular metabolism and prevent metabolic reprogramming by oxidative stress. AC16 cardiomyocytes in culture were treated with commonly used cardioplegic solutions, High K+ (HK), Low K+ (LK), Del Nido (DN), histidine-tryptophan-ketoglutarate (HTK), or Celsior (CS). The overall metabolic profile shown by the principal component analysis (PCA) and heatmap revealed that HK or LK had a minimal impact on the baseline 78 metabolites, whereas HTK or CS significantly repressed the levels of multiple amino acids and sugars. H2O2-induced sublethal mild oxidative stress causes decreases in NAD, nicotinamide, or acetylcarnitine, but increases in glucose derivatives, including glucose 6-P, glucose 1-P, fructose, mannose, and mannose 6-P. Additional increases include metabolites of the pentose phosphate pathway, D-ribose-5-P, L-arabitol, adonitol, and xylitol. Pretreatment with HK or LK cardioplegic solution prevented most metabolic changes and increases of reactive oxygen species (ROS) elicited by H2O2. Our data indicate that HK and LK cardioplegic solutions preserve baseline metabolism and protect against metabolic reprogramming by oxidative stress.

Restoration of NRF2 attenuates myocardial ischemia reperfusion injury through mediating microRNA-29a-3p/CCNT2 axis

Accumulated studies have been implemented for comprehending the mechanism of myocardial ischemia reperfusion injury (MI/RI). Nuclear factor erythroid-2 related factor 2 (NRF2)-mediated transcription activity in MI/RI has not been completely interpreted from the perspective of microRNA-29a-3p (miR-29a-3p) and cyclin T2 (CCNT2). Therein, this study intends to decode the mechanism of NRF2/miR-29a-3p/CCNT2 axis in MI/RI. Rat MI/RI models were established by left anterior descending artery ligation. Rats were injected with NRF2 or CCNT2 overexpression plasmids or miR-29a-3p agomir to explore their effects on MI/RI. Hypoxia/reoxygenation (H/R) cardiomyocytes were established and transfected with restored NRF2 or miR-29a-3p or CCNT2 for further exploration of their roles. NRF2, miR-29a-3p, and CCNT2 expression in myocardial tissues in rats with MI/RI and in cardiomyocytes in H/R injury were detected. ChIP assay verified the relationship between miR-29a-3p and NRF2, and the bioinformatics software and dual-luciferase reporter experiment verified the interaction between miR-29a-3p and CCNT2. NRF2 and miR-29a-3p were down-regulated while CCNT2 was up-regulated in myocardial tissues in rats with MI/RI and in H/R-treated cardiomyocytes. Restoration of NRF2 or miR-29a-3p improved hemodynamics and myocardial injury and suppressed serum inflammation and cardiomyocyte apoptosis via CCNT2 in rats with MI/RI. Upregulation of NRF2 or miR-29a-3p inhibited LDH and CK-MB activities, oxidative stress, and apoptosis and promoted viability of cardiomyocytes with H/R injury. NRF2 bound to the promoter of miR-29a-3p and CCNT2 was targeted by miR-29a-3p. This study elucidates that up-regulating NRF2 or miR-29a-3p attenuates MI/RI via inhibiting CCNT2, which may renew the existed knowledge of MI/RI-related mechanism and provide a novel guidance toward MI/RI treatment.

Enhanced Activity by NKCC1 and Slc26a6 Mediates Acidic pH and Cl- Movement after Cardioplegia-Induced Arrest of db/db Diabetic Heart

Diabetic heart dysfunctions during cardiac surgeries have revealed several clinical problems associated with ion imbalance. However, the mechanism of ion imbalance mediated by cardioplegia and a diabetic heart is largely unclear. We hypothesized that ion transporters might be regulated differently in the diabetic heart and that the differentially regulated ion transporters may involve in ion imbalance of the diabetic heart after cardioplegic arrest. In this study, we modified the Langendorff-free cardioplegia method and identified the involved ion transporters after cardioplegia-induced arrest between wild type and db/db heart. Enhanced expression of Na⁺-K⁺-2Cl⁻ cotransporter 1 (NKCC1) was observed in the db/db heart compared to the wild type heart. Enhanced NKCC1 activity was observed in the left ventricle of db/db mice compared to that of wild type after cardioplegia-induced arrest. The expression and activity of Slc26a6, a dominant Cl⁻/HCO₃⁻ exchanger in cardiac tissues, were enhanced in left ventricle strips of db/db mice compared to that of wild type. The Cl⁻ transporting activity in left ventricle strips of db/db mice was dramatically increased as compared to that of wild type. Interestingly, expression of Slc26a6, as well as carbonic anhydrase IV as a supportive enzyme of Slc26a6, was increased in db/db cardiac strips compared to wild type cardiac strips. Thus, the enhanced Cl⁻ transporting activity and expression by NKCC1 and Slc26a6 in db/db cardiac tissues after cardioplegia-induced arrest provide greater insight into enhanced acidosis and Cl⁻ movement-mediated db/db heart dysfunction. Thus, we suggested that enhanced Cl⁻ influx and HCO₃⁻ efflux through NKCC1 and Slc26a6 offer more acidic circumstances in the diabetic heart after cardioplegic arrest. These transporters should be considered as potential therapeutic targets to develop the next generation of cardioplegia solution for protection against ischemia-reperfusion injury in diabetic hearts.

Novel cardioprotection strategies for the aged heart: evidence from pre-clinical studies

The incidence of cardiovascular disease is rising as the population ages. This has led to an increase in the need to perform cardiac surgery in older patients. However, aged hearts are particularly susceptible to reperfusion injury following periods of myocardial ischaemia that occur during cardiac surgery. Indeed, older adults experience myocardial dysfunction and reduced survival post-surgery compared to younger people and certain groups, including older women and frail older adults, are at particular risk. This highlights the need to design cardioprotective strategies specifically for the ageing heart. Cardioprotection during surgery is often accomplished by perfusing the heart with chemical arresting agents, known as cardioplegic solutions. New protective strategies have been developed and tested in animal models, where cardioplegic solutions have been modified by changing their temperature, chemical components and/or the frequency of delivery. In addition, drugs designed to activate cardioprotective mechanisms or to inhibit mechanisms involved in injury have been added to improve the efficacy of these solutions. However, most experimental studies have developed and optimized cardioplegic solutions in hearts from younger male animals. This review discusses pre-clinical models used to optimize cardioplegic solutions, with an emphasis on the few studies that have used hearts from older animals. Pharmacologic agents that have been shown to enhance the benefits of cardioplegia in younger hearts and could, in theory, protect vulnerable older hearts are also considered. We emphasize the need to conduct studies in frail older animals of both sexes to facilitate translation of laboratory-based observations to the clinic.