Pericardial injection of micronized matrix biomaterial for post-infarct cardiac repair

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.