Pro-regenerative microRNAs delivered in the sub-acute phase of experimental myocardial infarction

A single intramyocardial injection of miR-199a right after myocardial infarction (MI) in the pre-clinical swine MI model resulted in almost complete recovery of normal cardiac functional parameters. However, persistent and unrestrained expression of the transgene produced sudden arrhythmic death of most treated animals. (Gabisonia et al. Nature 2019) The aim of this study was to test, in infarcted pig hearts, whether the beneficial effects of miR-199a delivered via AAV in sub-acute MI was equally pro-regenerative but devoid of arrhythmogenic effects. MI was induced with a closed-chest protocol utilizing coronary angiography technics. An ultrasound-guided right femoral arterial access was established and the left anterior descending artery (LAD) was closed for 90 minutes under fluoroscopic guidance. All the experimental animals underwent baseline cardiac MRI to evaluate heart functional parameters and scar dimensions. Two weeks after infarction open-heart surgery was performed and animals were intramyocardially injected in twenty different sites along the infarct border zone with either 2 × 1013 empty AAV6 (control group; n=5) particles or the same dose of AAV6-miR-199a (treated group; n=5). One month after the injection, animals underwent second CMR to assess changes in cardiac function and scar dimensions over time. Scar mass and LVEF were not significantly different at baseline between the treated and non-treated groups (9.7g ± 2.2g vs 10.2g ± 3.1g NS and 61.4% ± 5.4% vs 58.9% ± 5.8% NS respectively) and did not considerably change one month after the injection (9.33g ± 3.2g vs 11g ± 2.8 g NS and 62.25% ± 6.2% vs 59% ± 5.9% NS). Although no beneficial effects of miR-199a have been shown in sub-acute MI, most of the treated pigs continued to die of sudden arrhythmic death. In order to define the effective therapeutic time window of the selected miRNA, an amendment was made to the previous protocol and the compound was injected one week after MI. The results yielded from the new protocol were similar to those obtained from the previous one; there were no statistically significant differences in scar dimensions and cardiac functional parameters between the treated (n=4) and non-treated (n=4) groups (Scar mass 9.8g ± 2g vs 10.4g ± 2.2g and LVEF 60% ± 4.4% vs 58.8 % ± 5.22%). To get more insight into the arrhythmia mechanism in the treated animals, six weeks after the injection when the arrhythmia occurrence is high, an electrophysiology study (EPS) was performed in both groups (AAV6-empty n=3 vs AAV6-miR-199a n=3). Compared to controls, treated animals showed a relative resistance even to multiple extrastimuli with short coupling periods, whereas all the controls died because of inducible ventricular arrhythmias. Based on the obtained data a more refined approach, such as endocardial mapping is warranted for the future studies to better describe underlying causes for ventricular arrhythmias. Taking into consideration the fact that miR-199a did not demonstrate any considerable beneficial effects when injected at the above-mentioned time points (one and two weeks after MI), further experiments are needed to precisely determine the therapeutic time window of the selected miRNA.