Human Muse cells reduce myocardial infarct size and improve cardiac function without causing arrythmias in a swine model of acute myocardial infarction

Abstract

Background: We recently reported that multilineage-differentiating stress enduring (Muse) cells intravenously administered after acute myocardial infarction (AMI), selectively engrafted to the infarct area, spontaneously differentiated into cardiomyocytes and vessels, reduced the infarct size, improved the left ventricular (LV) function and remodeling in rabbits. We aimed to clarify the efficiency of Muse cells in a larger animal AMI model of mini-pigs using a semi-clinical grade human Muse cell product.

Method and result: Mini-pigs underwent 30 min of coronary artery occlusion followed by 2 weeks of reperfusion. Semi-clinical grade human Muse cell product (1x107, Muse group, n = 5) or saline (Vehicle group, n = 7) were intravenously administered at 24 h after reperfusion. The infarct size, LV function and remodeling were evaluated by echocardiography. Arrhythmias were evaluated by an implantable loop recorder. The infarct size was significantly smaller in the Muse group (10.5±3.3%) than in the Vehicle group (21.0±2.0%). Both the LV ejection fraction and fractional shortening were significantly greater in the Muse group than in the Vehicle group. The LV end-systolic and end-diastolic dimensions were significantly smaller in the Muse group than in the Vehicle group. Human Muse cells homed into the infarct border area and expressed cardiac troponin I and vascular endothelial CD31. No arrhythmias and no blood test abnormality were observed.

Conclusion: Muse cell product might be promising for AMI therapy based on the efficiency and safety in a mini-pig AMI.

Fig 1. Cardiac function and myocardial infarct size.

A: Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) in the Vehicle (n = 7) and Muse (n = 5) groups. B: Representative echocardiography in Vehicle and Muse groups. C: Left ventricular ejection fraction (LVEF), LV fractional shortening (LVFS), LV end-diastolic dimension (LVEDd), and LV end-systolic dimension (LVESd) in the Vehicle (n = 7) and Muse (n = 5) groups. D: Representative pictures of the Masson-Trichrome staining of cross-sections of LV in the Vehicle and Muse groups. Blue color-coded areas indicate the infarct regions and red-coded areas indicate the non-infarct regions of LV. E: Fibrosis area (mm²/slice/kg) in the Vehicle (n = 7) and Muse (n = 5) groups. F: Infarct size as a percentage of LV area (%) in the Vehicle (n = 7) and Muse (n = 5) groups.

Fig 2. Differentiation of Muse cells into cardiomyocytes.

A: GFP-labelled Muse cells and cardiac troponin I in the infarct border area. GFP (green) and troponin I (Red) are merged, suggesting that GFP-labelled Muse cells differentiated into cardiomyocytes. Bar = 50 μm. B: Negative control in the infarct border area. Troponin I positive cells (red), DAPI (blue), Bar = 50 μm. C: GFP (green)-labelled Muse cells are engrafted in the infarct border area. Bar = 100 μm.

Fig 3. Differentiation of Muse cells into vessels.

A: GFP-labelled Muse cells and CD31-positive microvessels in the infarct border area. GFP (green) and CD31 (Red) are merged, suggesting that GFP-labelled Muse cells differentiated into vascular endothelium. Bar = 50 μm. B: Negative control in the infarct border area. CD31 (red), DAPI (blue), Bar = 25 μm. C: Typical pictures of CD31-positive microvessels by immunohistological staining in the Vehicle and Muse groups. Bars = 50 μm. D: The number of CD31-positive microvessels by immunohistological staining is significantly greater in the Muse (n = 5) group than in the Vehicle (n = 7) group.

Fig 4. Analysis of arrythmias using an implantable loop recorder.

A: Implantable loop recorder. B, C: Episode summary for 2 weeks in a case of Muse groups, showing no arrythmias such as bradycardia, pause except for tachycardia. we see the recorded electrocardiogram as shown in C, this was judged as a 300/min of tachycardia in the loop recorder. However, careful analysis of electrocardiogram revealed that the recorder judged T wave and R wave as a one beat and then the heart rate was regarded as a 300/min of tachycardia, but it was actually a 150/min of heart rate. Therefore, this was not a real tachycardia of 300/min.