Engineered Heart Tissue (EHT) can be utilized to partially repair infarcted myocardium in rats. Here, we investigated the feasibility of EHT-grafts as transmural wall replacement in a heterotopic transplantation model.
Methods:
EHTs (diameter: 15 mm, thickness: 1– 4 mm) were generated from 12.5 ×10
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neonatal rat heart cells, collagen type I, and matrigel. Similarly, non-contractile constructs were generated from rat cardiac fibroblasts (FB) and mesenchymal stem cells (MSC). Grafts were surgically inserted into large transmural defects (diameter: 6 mm) in the left ventricle of explanted donor hearts. Subsequently, “treated” hearts were transplanted into weight-matched (308±12 g; n=14), immune suppressed (cyclosporine, azathioprine, prednisolone) Wistar rats in heterotopic position. All transmural defects were also covered with an aortic patch to prevent bleeding from the ventricles. Sham surgeries included aortic patch implantations only. Heterotopic hearts were harvested after 28 days and subjected to morphological analyses by confocal laser scanning microscopy (CLSM).
Results:
Heart transplant weight at the time of implantation was 1.1±0.02 g (n=14). Heterotopic heart weight increased substantially in Sham (2.4±0.3 g, n=3) and FB-graft (2.1±0.1 g, n=3) animals, whereas MSC- (1.7±0.2 g, n=4) and EHT-graft (1.3±0.1 g, n=4; p<0.05 vs. Sham) animals showed a smaller or no increase in weight, respectively. EHT grafts remained contractile throughout the observation period. CLSM revealed that EHT-grafts established oriented muscle bundles (actin and actinin staining) inside the transmural defects and were strongly vascularized (CD31 and smooth muscle actin staining; lectin labeling) leading to partial reconstitution of the myocardial continuity. This was not observed in animals with FB- and MSC-grafts. However, MSC-grafts, but not FB-grafts, contained newly formed vessels with a markedly larger diameter than observed in EHT-grafts (21±6 vs. 5±0.7 μm; p<0.05).
Conclusion:
EHTs can be utilized as myocardial tissue grafts to reconstruct and prevent pathological enlargement of the left ventricle. This study constitutes a first step to establish a novel transmural myocardial repair technology involving fully bioengineered heart muscle.
