Autologous Mesenchymal Stem Cells in Experimental Mitral Valve Regurgitation of Dogs Attenuated Collagen Loss and Dysfunctional Myocardial Remodeling
In early mitral valve regurgitation (MR) of dogs, increases in left ventricular (LV) diastolic wall stress induces neurohormonal and interstitial activity, including mast cell recruitment, the dissolution of collagen in the cardiac extracellular matrix (ECM), and elongation of cardiomyocytes. In ischemic cardiomyopathy, mesenchymal stem cells (MSCs) were capable of transforming into myofibroblasts and attenuating additional myocyte loss. The purpose of this study was to determine if implantated MSCs in dogs with MR and volume overload would: 1) remain at the site of the injection in the absence of inflammation, 2) alter the collagen matrix in the ECM, 3) vary the activity of interstitial mast cells, and 4) alter the mRNA LV profile. Seven intact mongrel dogs without known heart disease had MSCs isolated from bone marrow samples using an accepted plastic adherence technique and each sample cultured. The MSCs were labeled with 0.9 μm polystyrene spheres impregnated with contrast agents of iron oxide (62.4%) microparticles and a fluorescein-5 isothiocyanate analog (Dragon Green). Viability of the cells ( > 70%) was determined by Trypan Blue exclusion; and fluorescein label was documented inside the MSCs.
On Day 1, MR was induced via chordal rupture using a fluoroscopic-guided catheterization method. Immediately after MR, a 1mL aliquot containing 2.18±0.82 x 107 (Range 1.0-3.5 x 107) of autologous labeled MSCs was injected into the LV free wall in a single location via LV needle catheter. On Day -7, Day 1 post-op, and Day 38, cardiac MRIs were recorded, wall stress and geometry calculated, and the MSC in LV located via the iron oxide. On Day 1 Pre and Post MR, and Day 40 hemodynamics were collected. After humane euthanasia, LV was collected from the MSC injection site, adjacent to the site, and distant from the site. Samples were evaluated for mRNA pathways, collagen density, mast cell counts, and histopathology.
In the area of MSC implantation, determined by Picric Acid Sirius Red stain, a significantly higher collagen volume percent was noted, suggesting fibroblast transformation by the MSCs. Hemodynamic decreases in forward cardiac output from baseline was significantly lower( p<0.05) in dogs treated with MSCs (19.7% ±7.5) than MR placebo dogs (n=4) (39.4%±9.2). Increases in SVR were also higher (p<0.05) in MR placebo dogs (84.6%±53.8) than MSC treated dogs (32.9%±21.0). By cardiac MRI, on Day 1 post MR and Day 38, MSCs were noted with no loss in signal. This data suggest autologous MSCs injected into the LV of dogs with early MR remained in the myocardium, promoted stabilization of the ECM and attenuated the initial dysfunctional cardiac remodeling. Global administration of MSCs may have clinical application in MR of dogs.