PERICARDIAL INJECTION OF MICRONIZED MATRIX BIOMATERIAL FOR POST-INFARCT CARDIAC REPAIR

Abstract

BACKGROUND Injection of micronized biomaterials into the pericardial space is a potential less invasive approach to enhance post-infarct cardiac repair (Image). We have shown that porcine small intestinal submucosal extracellular matrix (SIS-ECM) biomaterials contain fibroblast growth factor-2 (FGF-2); and epicardial application of a SIS-ECM patch over ischemic myocardium promotes reparative post-infarct cardiac remodeling by upregulating vasculogenesis and downregulating fibrosis. Micronizing SIS-ECM into an injectable platform will allow pericardial delivery without the need for invasive surgery. Herein, we demonstrate improved post-infarct cardiac recovery after delivering micronized SIS-ECM powder into the pericardial space in in mice and we explore cellular mechanisms using three-dimensional fibroblast cultures. METHODS AND RESULTS In an intact pericardium mouse infarct model, coronary ligation (infarct) was performed through an unopened/undisrupted pericardium followed by pericardial injection of micronized SIS-ECM suspended in saline (treatment; n=12) or saline (control; n=10). Pressure-volume loops assessed cardiac function after 28 days. Mice receiving pericardial injection of micronized SIS-ECM had higher ejection fraction, lower ventricular stiffness (end diastolic pressure volume relationship; EDPVR), higher stroke work and higher cardiac output compared to saline control. Improved diastolic function represented by ventricular stiffness is suggestive of attenuated fibrosis and improved ventricular compliance. Three-dimensional cell cultures of mouse 3T3 cell line fibroblasts in collagen matrices assessed cellular response when exposed to either biomaterial-conditioned media with eluted growth factors (treatment) or untreated media (control). Collagen gels contract when fibroblasts take on a profibrotic phenotype, reducing in size on a macroscopic level. Additionally, paracrine activity of fibroblasts is measured using multiplex analysis with focus on angiogenic VEGF protein and fibrotic MMP-2 protease. Collagen gel contraction and MMP-2 release were attenuated by biomaterial factors, suggesting reduced fibrotic activity. Micronized SIS-ECM increased VEGF production from fibroblasts. Adding an FGF-2 inhibitor to biomaterial-conditioned media negated the biomaterial's effects, thereby increasing gel contraction and MMP-2 release, highlighting the key role of FGF-2 in attenuating fibroblast activity. Table 1 contains outcomes from all studies. CONCLUSION Pericardial injection of micronized SIS-ECM promotes reparative fibroblast activity, increases production of angiogenic VEGF protein, and preserves post-infarct cardiac compliance and function. Pericardial injection is a less invasive modality that may facilitate early intervention to attenuate maladaptive post-infarct structural remodeling. Future study into mechanism and large animal infarct models will be required to identify key cellular pathways and develop percutaneous strategies for clinical translation. Injection of micronized biomaterials into the pericardial space is a potential less invasive approach to enhance post-infarct cardiac repair (Image). We have shown that porcine small intestinal submucosal extracellular matrix (SIS-ECM) biomaterials contain fibroblast growth factor-2 (FGF-2); and epicardial application of a SIS-ECM patch over ischemic myocardium promotes reparative post-infarct cardiac remodeling by upregulating vasculogenesis and downregulating fibrosis. Micronizing SIS-ECM into an injectable platform will allow pericardial delivery without the need for invasive surgery. Herein, we demonstrate improved post-infarct cardiac recovery after delivering micronized SIS-ECM powder into the pericardial space in in mice and we explore cellular mechanisms using three-dimensional fibroblast cultures. In an intact pericardium mouse infarct model, coronary ligation (infarct) was performed through an unopened/undisrupted pericardium followed by pericardial injection of micronized SIS-ECM suspended in saline (treatment; n=12) or saline (control; n=10). Pressure-volume loops assessed cardiac function after 28 days. Mice receiving pericardial injection of micronized SIS-ECM had higher ejection fraction, lower ventricular stiffness (end diastolic pressure volume relationship; EDPVR), higher stroke work and higher cardiac output compared to saline control. Improved diastolic function represented by ventricular stiffness is suggestive of attenuated fibrosis and improved ventricular compliance. Three-dimensional cell cultures of mouse 3T3 cell line fibroblasts in collagen matrices assessed cellular response when exposed to either biomaterial-conditioned media with eluted growth factors (treatment) or untreated media (control). Collagen gels contract when fibroblasts take on a profibrotic phenotype, reducing in size on a macroscopic level. Additionally, paracrine activity of fibroblasts is measured using multiplex analysis with focus on angiogenic VEGF protein and fibrotic MMP-2 protease. Collagen gel contraction and MMP-2 release were attenuated by biomaterial factors, suggesting reduced fibrotic activity. Micronized SIS-ECM increased VEGF production from fibroblasts. Adding an FGF-2 inhibitor to biomaterial-conditioned media negated the biomaterial's effects, thereby increasing gel contraction and MMP-2 release, highlighting the key role of FGF-2 in attenuating fibroblast activity. Table 1 contains outcomes from all studies. Pericardial injection of micronized SIS-ECM promotes reparative fibroblast activity, increases production of angiogenic VEGF protein, and preserves post-infarct cardiac compliance and function. Pericardial injection is a less invasive modality that may facilitate early intervention to attenuate maladaptive post-infarct structural remodeling. Future study into mechanism and large animal infarct models will be required to identify key cellular pathways and develop percutaneous strategies for clinical translation.