An in vitro drug-induced cardiotoxicity assay is a critical step in drug discovery for clinical use. The use of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is promising for this purpose. However, single hiPSC-CMs are limited in their ability to mimic native cardiac tissue structurally and functionally, and the generation of artificial cardiac tissue using hiPSC-CMs is an ongoing challenging. We therefore developed a new method of constructing three-dimensional (3D) artificial tissues in a short time by coating extracellular matrix (ECM) components on cell surfaces. We hypothesized that 3D cardiac tissues derived from hiPSC-CMs (3D-hiPSC-CT) could be used for an in vitro drug-induced cardiotoxicity assay. 3D-hiPSC-CT were generated by fibronectin and gelatin nanofilm coated single hiPSC-CMs. Histologically, 3D-hiPSC-CT exhibited a sarcomere structure in the myocytes and ECM proteins, such as fibronectin, collagen type I/III, and laminin. The administration of cytotoxic doxorubicin at 5.0 μM induced the release of lactate dehydrogenase, while that at 2.0 μM reduced the cell viability. E-4031, human ether-a-go-go related gene (hERG)-type potassium channel blocker, and isoproterenol induced significant changes both in the Ca transient parameters and contractile parameters in a dose-dependent manner. The 3D-hiPSC-CT exhibited doxorubicin-sensitive cytotoxicity and hERG channel blocker/isoproterenol-sensitive electrical activity in vitro, indicating its usefulness for drug-induced cardiotoxicity assays or drug screening systems for drug discovery.

Recent advances in intravital microscopy have provided insight into dynamic biological events at the cellular level in both healthy and pathological tissue. However, real-time in vivo cellular imaging of the beating heart has not been fully established, mainly due to the difficulty of obtaining clear images through cycles of cardiac and respiratory motion. Here we report the successful recording of clear in vivo moving images of the beating rat heart by two-photon microscopy facilitated by cardiothoracic surgery and a novel cardiac stabiliser. Subcellular dynamics of the major cardiac components including the myocardium and its subcellular structures (i.e., nuclei and myofibrils) and mitochondrial distribution in cardiac myocytes were visualised for 4–5 h in green fluorescent protein-expressing transgenic Lewis rats at 15 frames/s. We also observed ischaemia/reperfusion (I/R) injury-induced suppression of the contraction/relaxation cycle and the consequent increase in cell permeability and leukocyte accumulation in cardiac tissue. I/R injury was induced in other transgenic mouse lines to further clarify the biological events in cardiac tissue. This imaging system can serve as an alternative modality for real time monitoring in animal models and cardiological drug screening, and can contribute to the development of more effective treatments for cardiac diseases.

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The degree or nature of functional mitral regurgitation (MR) is not necessarily correlated with the size or function of the left ventricle (LV). We hypothesized that the anatomical structure of the mitral valve (MV) complex might play a role in functional MR in ischemic or nonischemic dilated cardiomyopathy (DCM).The structure of the LV and MV complex in DCM patients (n = 29) was assessed using electrocardiogram-gated 320-slice computed tomography and was compared with that in healthy patients (n = 12). Twenty-five DCM patients with mild or low MR (DCM-lowMR) had markedly greater length, diameter, and sphericity index of the LV and a larger tenting area than the controls. The distance between the papillary muscle (PM) tip and the mitral annular plane was not different between DCM-lowMR and normal hearts despite the greater LV length observed in DCM-lowMR. Furthermore, DCM-lowMR had markedly longer chordae tendineae (DCM-lowMR: 24 [20-26] mm; controls: 14 [13-16] mm; P < 0.01) and larger anterior leaflets (DCM-lowMR: 30 [27-31] mm; controls: 22 [20-24] mm; P < 0.01), thus suggesting the adaptive remodeling of the MV complex. Four DCM patients with moderate-severe MR had unbalanced remodeling, such as excessive LV dilatation, short anterior mitral leaflets, and short chordae tendineae.The development of functional MR might be associated with the remodeling of LV and MV components, such as the PMs, chordae tendineae, or anterior MV leaflets. Detailed anatomical assessments of the LV and MV complex would contribute to the adequate staging of ischemic or nonischemic DCM.