Assessment of cardiac toxicity of manganese chloride for cardiovascular magnetic resonance

Abstract

MRI is widely used in cardiology to visualize the structure and function of the heart. Currently gadolinium is the contrast agents use to improve sensitivity and specificity of diagnostic images, enabling the assessment of scar and fibrosis. Manganese-based contrast molecules are being developed with the hope to improve the diagnosis of cardiac pathologies. Manganese, a calcium analogue, allows detection of viable cells within altered tissue. However, the cardiac safety of manganese is not fully assessed. To characterize the effect of MnCl2 on cardiac function and electrical parameters. Hemodynamic function was determined ex vivo using the isolated working rat heart preparation. HL-1 cell line was used to investigate cell viability (loading with calcein AM) and calcium cycling (loading with CAL-520 AM). Rat ventricular cardiomyocytes were dissociated by enzymatic digestion. Action potentials and calcium currents were recorded using the patch clamp technique. The effect of ascending concentrations of MnCl2 (1, 10, 25, 50 and 100 μM) were evaluated. MRI experiments (1.5 T and 9.4 T) were performed on formalin-fixed rat hearts, previously perfused with 25 or 100 μM of MnCl2. Left ventricular hemodynamic parameters from isolated working hearts show that heart rate is not modified by μM [MnCl2]. Similar observation was made for contractility index and aortic flow up to 50 μM; 100 μM MnCl2 induced a significant decrease of the two parameters. At the cellular level, μM [MnCl2] did not impact HL-1 cell viability. The amplitude of the calcium transients was significantly reduced only at 100 μM of MnCl2 ( P < 0.05). In isolated ventricular myocytes, action potential duration at 20%, 50% and 90% of repolarization were not modified up to 10 μM of MnCl2. A small but significant decrease of action potential duration was observed at 25, 50 and 100 μM (APD90 decrease by 23 ± 6% vs control). Peak L-type calcium current amplitude was significantly decreased by 50 and 100 μM of MnCl2. MRI on heart perfused with 25 μM of MnCl2 (no impact hemodynamic function) and 100 μM of MnCl2 showed a dose dependent decrease in the T1 relaxation time, a parameter for altered and disease state. Our results show that μM [MnCl2] (up to 25 μM) can be used as a contrast agent in MRI, without effects on cardiac hemodynamic parameters. MRI with manganese should therefore enable visualization of viable and stunned myocardium.