Stimulation of angiogenesis through growth factor delivery from synthetic heparinised hydrogels

Objectives: Vascular diseases are one of the leading causes of death. Due to minimal regenerative capability of the heart, alternative therapies have been sought after with engineered biomaterials being extensively investigated in this area. In this study, enzymatically degradable heparinised polyethylene glycol (PEG-Hep) hydrogels were synthesized and characterised for the binding and controlled release of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), as well as their bioactivity and angiogenic potential in vivo. Methodology: VEGF and bFGF were combined into 4% (m/v) PEG-Hep hydrogels. The binding and release rates of VEGF and BFGF were analysed via an immunosorbent assay. Released growth factor bioactivity was measured using an XTT metabolic assay on human saphenous vein endothelial cells and human dermal fibroblasts. Neovascularisation was quantified in a subcutaneous rat angiogenesis model in which hydrogel growth factor combinations were implanted within porous polyurethane discs and analysed after a 4 week period. A novel hybrid hydrogel able to degrade proteolytically and hydrolytically was further developed, characterised and analysed as above. Results: PEG-Hep hydrogels demonstrated substantial growth factor binding ability (500-600 ng) and allowed sustained release (10-20 ng/day) for up to 28 days. Bioactivity of the growth factors was retained throughout the release period. The degradation rate of the hydrogels could be controlled in vivo by varying the ratio of monomers capable of forming either hydrolytically or proteolytically degradable crosslinks. Qualitative and quantitative analysis demonstrated a pronounced and significant angiogenic response in vivo (p<0.05). Conclusion: Heparinised PEG hydrogels show significant promise as controlled release vehicles for growth factors and warrant further examination in a myocardial infarction model

Synthetic extracellular matrix mimic hydrogel improves efficacy of mesenchymal stromal cell therapy for ischemic cardiomyopathy.

BACKGROUND: Mesenchymal stromal cells (MSC) repair infarcted hearts mainly through paracrine mechanisms. Low cell engraftment limits the release of soluble paracrine factors (SF) over time and, consequently, MSC efficacy. We tested whether a synthetic extracellular matrix mimic, a hydrogel containing heparin (H-HG), could ameliorate MSC engraftment and binding/release of SF, thus improving MSC therapy efficacy. METHODS AND RESULTS: In vitro, rat bone-marrow MSC (rBM-MSC) were seeded and grown into H-HG. Under normoxia, the hydrogel did not affect cell survival (rBM-MSC survival >90% at each time point tested); vice versa, under hypoxia the biomaterial resulted to be protective for the cells (p < .001 vs rBM-MSC alone). H-HG or control PEG hydrogels (HG) were incubated with VEGF or bFGF for binding/release quantification. Data showed significantly higher amount of VEGF and bFGF bound by H-HG compared with HG (p < .05) and a constant release over time. In vivo, myocardial infarction (MI) was induced in female Sprague Dawley rats by permanent coronary ligation. One week later, saline, rBM-MSC, H-HG or rBM-MSC/H-HG were injected in the infarct zone. The co-injection of rBM-MSC/H-HG into infarcted hearts significantly increased cardiac function. Importantly, we observed a significant gain in MSC engraftment, reduction of ventricular remodeling and stimulation of neo-vasculogenesis. We also documented higher amounts of several pro-angiogenic factors in hearts treated with rBM-MSC/H-HG. CONCLUSIONS: Our data show that H-HG increases MSC engraftment, efficiently fine tunes the paracrine MSC actions and improves cardiac function in infarcted rat hearts. STATEMENT OF SIGNIFICANCE: Transplantation of MSC is a promising treatment for ischemic heart disease, but low cell engraftment has so far limited its efficacy. The enzymatically degradable H-HG that we developed is able to increase MSC retention/engraftment and, at the same time, to fine-tune the paracrine effects mediated by the cells. Most importantly, the co-transplantation of MSC and H-HG in a rat model of ischemic cardiomyopathy improved heart function through a significant reduction in ventricular remodeling/scarring and amelioration in neo-vasculogenesis/endogenous cardiac regeneration. These beneficial effects are comparable to those obtained by others using a much greater number of cells, strengthening the efficacy of the biomaterial used in increasing the therapeutic effects of MSC. Given its efficacy and safety, documented by the absence of immunoreaction, our strategy appears readily translatable to clinical scenarios