Using Diffusion Tensor Imaging to Depict Changes After Matured Pluripotent Stem Cell-Derived Cardiomyocytes Transplantation

Background Novel treatment strategies are needed to improve the structure and function in the myocardium post infarction. In vitro-matured pluripotent stem cell-derived cardiomyocytes (PSC-CMs), have been shown to be a promising regenerative strategy. We hypothesized that mature PSC-CMs will have anisotropic structure and improved cell alignment when compared to immature PSC-CMs using magnetic resonance imaging (MRI) in a guinea pig model of cardiac injury. Methods Guinea pigs (n=16) were cryoinjured on day -10, followed by transplantation of either 108 polydimethylsiloxane-matured PSC-CMs (PDMS, n=6) or 108 immature tissue culture plastic-generated PSC-CMs (TCP, n=6) on day 0. Vehicle (sham-treated) subjects were injected with a pro-survival cocktail devoid of cells (n=4), while healthy controls (n=4) did not undergo cryoinjury or treatment. Animals were sacrificed on either day +14 or day +28 post transplantation.Animals were imaged ex vivo on a 7T Bruker MRI. A 3D Diffusion Tensor Imaging sequence was used to quantify structure via fractional anisotropy (FA), mean diffusivity (MD) and myocyte alignment measured by the standard deviation of the transverse angle (TA). Results MD and FA of mature PDMS grafts demonstrated anisotropy that were not significantly different than the healthy control hearts (MD=1.1 ± 0.12 ×10-3 mm2/s vs. 0.93 ± 0.01 ×10-3 mm2/s, p=0.4 and FA=0.22±0.05 vs. 0.26±0.001, p=0.5). Immature TCP grafts exhibited significantly higher MD than the healthy control (1.3 ± 0.08 ×10-3 mm2/s, p<0.05) and significantly lower FA than the control (0.12±0.02, p< 0.05) but were not different from mature PDMS grafts in this small cohort.TA of healthy controls showed low variability and were not significantly different than mature PDMS grafts (p=0.4) while immature TCP grafts were significantly different (p<0.001). Discussion DTI parameters of mature graft tissue trended towards that of the healthy myocardium, indicating the grafted cardiomyocytes may have a similar phenotype to healthy tissue. Contrast-enhanced MR images corresponded well to histological staining, demonstrating a non-invasive method of localizing the repopulated cardiomyocytes within the scar. Conclusions The DTI measures within graft tissue were indicative of anisotropic structure, and showed greater myocyte organization compared to the scarred territory. These findings show that MRI is a valuable tool to assess structural impacts of regenerative therapies.