AimsIncreasing energy storage capacity by elevating creatine and phosphocreatine (PCr) levels to increase ATP availability is an attractive concept for protecting against ischaemia and heart failure. However, testing this hypothesis has not been possible since oral creatine supplementation is ineffectual at elevating myocardial creatine levels. We therefore used mice overexpressing creatine transporter in the heart (CrT-OE) to test for the first time whether elevated creatine is beneficial in clinically relevant disease models of heart failure and ischaemia/reperfusion (I/R) injury.Methods and resultsCrT-OE mice were selected for left ventricular (LV) creatine 20–100% above wild-type values and subjected to acute and chronic coronary artery ligation. Increasing myocardial creatine up to 100% was not detrimental even in ageing CrT-OE. In chronic heart failure, creatine elevation was neither beneficial nor detrimental, with no effect on survival, LV remodelling or dysfunction. However, CrT-OE hearts were protected against I/R injury in vivo in a dose-dependent manner (average 27% less myocardial necrosis) and exhibited greatly improved functional recovery following ex vivo I/R (59% of baseline vs. 29%). Mechanisms contributing to ischaemic protection in CrT-OE hearts include elevated PCr and glycogen levels and improved energy reserve. Furthermore, creatine loading in HL-1 cells did not alter antioxidant defences, but delayed mitochondrial permeability transition pore opening in response to oxidative stress, suggesting an additional mechanism to prevent reperfusion injury.ConclusionElevation of myocardial creatine by 20–100% reduced myocardial stunning and I/R injury via pleiotropic mechanisms, suggesting CrT activation as a novel, potentially translatable target for cardiac protection from ischaemia.

Background-Heart failure is associated with deranged cardiac energy metabolism, including reductions of creatine and phosphocreatine. Interventions that increase myocardial high-energy phosphate stores have been proposed as a strategy for treatment of heart failure. Previously, it has not been possible to increase myocardial creatine and phosphocreatine concentrations to supranormal levels because they are subject to tight regulation by the sarcolemmal creatine transporter (CrT). Methods and Results-We therefore created 2 transgenic mouse lines overexpressing the myocardial creatine transporter (CrT-OE). Compared with wild-type (WT) littermate controls, total creatine (by high-performance liquid chromatography) was increased in CrT-OE hearts (66Ϯ6 nmol/mg protein in WT versus 133Ϯ52 nmol/mg protein in CrT-OE). Phosphocreatine levels (by 31 P magnetic resonance spectroscopy) were also increased but to a lesser extent. Surprisingly, CrT-OE mice developed left ventricular (LV) dilatation (LV end-diastolic volume: 21.5Ϯ4.3 L in WT versus 33.1Ϯ9.6 L in CrT-OE; Pϭ0.002), substantial LV dysfunction (ejection fraction: 64Ϯ9% in WT versus 49Ϯ13% in CrT-OE; range, 22% to 70%; Pϭ0.003), and LV hypertrophy (by 3-dimensional echocardiography and magnetic resonance imaging). Myocardial creatine content correlated closely with LV end-diastolic volume (rϭ0.51, Pϭ0.02), ejection fraction (rϭϪ0.74, Pϭ0.0002), LV weight (rϭ0.59, Pϭ0.006), LV end-diastolic pressure (rϭ0.52, Pϭ0.02), and dP/dt max (rϭϪ0.69, Pϭ0.0008). Despite increased creatine and phosphocreatine levels, CrT-OE hearts showed energetic impairment, with increased free ADP concentrations and reduced free-energy change levels. Conclusions-Overexpression of the CrT leads to supranormal levels of myocardial creatine and phosphocreatine, but the heart is incapable of keeping the augmented creatine pool adequately phosphorylated, resulting in increased free ADP levels, LV hypertrophy, and dysfunction. Our data demonstrate that a disturbance of the CrT-mediated tight regulation of cardiac energy metabolism has deleterious functional consequences. These findings caution against the uncritical use of creatine as a therapeutic agent in heart disease. (Circulation. 2005;112:3131-3139.)

Background-The role of the creatine kinase (CK)/phosphocreatine (PCr) energy buffer and transport system in heart remains unclear. Guanidinoacetate-N-methyltransferase-knockout (GAMT Ϫ/Ϫ ) mice represent a new model of profoundly altered cardiac energetics, showing undetectable levels of PCr and creatine and accumulation of the precursor (phospho-)guanidinoacetate (P-GA). To characterize the role of a substantially impaired CK/PCr system in heart, we studied the cardiac phenotype of wild-type (WT) and GAMT Ϫ/Ϫ mice. Methods and Results-GAMTϪ/Ϫ mice did not show cardiac hypertrophy (myocyte cross-sectional areas, hypertrophy markers atrial natriuretic factor and ␤-myosin heavy chain). Systolic and diastolic function, measured invasively (left ventricular conductance catheter) and noninvasively (MRI), were similar for WT and GAMT Ϫ/Ϫ mice. However, during inotropic stimulation with dobutamine, preload-recruitable stroke work failed to reach maximal levels of performance in GAMT Ϫ/Ϫ hearts (101Ϯ8 mm Hg in WT versus 59Ϯ7 mm Hg in GAMT Ϫ/Ϫ ; PϽ0.05). 31 P-MR spectroscopy experiments showed that during inotropic stimulation, isolated WT hearts utilized PCr, whereas isolated GAMT

Mito-CK-/- and M/Mito-CK-/- mice show significant LV dilatation and marked LV hypertrophy, but LV remodeling post-MI is not aggravated. CK ablation leads to substantial adaptational changes in heart.