Hyaluronic acid-serum hydrogels rapidly restore metabolism of encapsulated stem cells and promote engraftment

Background: Cell death due to anoikis, necrosis and cell egress from transplantation sites limits functional benefits of cellular cardiomyoplasty. Cell dissociation and suspension, which are a pre-requisite for most cell transplantation studies, lead to depression of cellular metabolism and anoikis, which contribute to low engraftment. Objective: We tissue engineered scaffolds with the goal of rapidly restoring metabolism, promoting viability, proliferation and engraftment of encapsulated stem cells. Methods: The carboxyl groups of HA were functionalized with N-hydroxysuccinimide (NHS) to yield HA succinimidyl succinate (HA-NHS) groups that react with free amine groups to form amide bonds. HA-NHS was cross-linked by serum to generate HA:Serum (HA:Ser) hydrogels. Physical properties of HA:Ser hydrogels were measured. Effect of encapsulating cardiosphere-derived cells (CDCs) in HA:Ser hydrogels on viability, proliferation, glucose uptake and metabolism was assessed in vitro. In vivo acute intra-myocardial cell retention of ¹⁸FDG-labeled CDCs encapsulated in HA:Ser hydrogels was quantified. Effect of CDC encapsulation in HA:Ser hydrogels on in vivo metabolism and engraftment at 7 days was assessed by serial, dual isotope SPECT-CT and bioluminescence imaging of CDCs expressing the Na-iodide symporter and firefly luciferase genes respectively. Effect of HA:Ser hydrogels ± CDCs on cardiac function was assessed at 7 days & 28 days post-infarct. Results: HA:Ser hydrogels are highly bio-adhesive, biodegradable, promote rapid cell adhesion, glucose uptake and restore bioenergetics of encapsulated cells within 1 h of encapsulation, both in vitro and in vivo. These metabolic scaffolds can be applied epicardially as a patch to beating hearts or injected intramyocardially. HA:Ser hydrogels markedly increase acute intramyocardial retention (~6 fold), promote in vivo viability, proliferation, engraftment of encapsulated stem cells and angiogenesis. Conclusion: HA:Ser hydrogels serve as 'synthetic stem cell niches' that rapidly restore metabolism of encapsulated stem cells, promote stem cell engraftment and angiogenesis. These first ever, tissue engineered metabolic scaffolds hold promise for clinical translation in conjunction with CDCs and possibly other stem cell types.