Preclinical evaluation of biopolymer-delivered circulating angiogenic cells in a swine model of hibernating myocardium

Targeted Myocardial Restoration with Injectable Hydrogels-In Search of The Holy Grail in Regenerating Damaged Heart Tissue

A 3-dimensional, robust, and sustained myocardial restoration by means of tissue engineering remains an experimental approach. Prolific protocols have been developed and tested in small and large animals, but, as clinical cardiac surgeons, we have not arrived at the privilege of utilizing any of them in our clinical practice. The question arises as to why this is. The heart is a unique organ, anatomically and functionally. It is not an easy target to replicate with current techniques, or even to support in its viability and function. Currently, available therapies fail to reverse the loss of functional cardiac tissue, the fundamental pathology remains unaddressed, and heart transplantation is an ultima ratio treatment option. Owing to the equivocal results of cell-based therapies, several strategies have been pursued to overcome the limitations of the current treatment options. Preclinical data, as well as first-in-human studies, conducted to-date have provided important insights into the understanding of injection-based approaches for myocardial restoration. In light of the available data, injectable biomaterials suitable for transcatheter delivery appear to have the highest translational potential. This article presents a current state-of-the-literature review in the field of hydrogel-based myocardial restoration therapy.

Delivering More of an Injectable Human Recombinant Collagen III Hydrogel Does Not Improve Its Therapeutic Efficacy for Treating Myocardial Infarction

Injectable hydrogels are a promising method to enhance repair in the heart after myocardial infarction (MI). However, few studies have compared different strategies for the application of biomaterial treatments. In this study, we use a clinically relevant mouse MI model to assess the therapeutic efficacy of different treatment protocols for intramyocardial injection of a recombinant human collagen III (rHCIII) thermoresponsive hydrogel. Comparing a single hydrogel injection at an early time point (3 h) versus injections at multiple time points (3 h, 1 week, and 2 weeks) post-MI revealed that the single injection group led to superior cardiac function, reduced scar size and inflammation, and increased vascularization. Omitting the 3 h time point and delivering the hydrogel at 1 and 2 weeks post-MI led to poorer cardiac function. The positive effects of the single time point injection (3 h) on scar size and vascular density were lost when the hydrogel's collagen concentration was increased from 1% to 2%, and it did not confer any additional functional improvement. This study shows that early treatment with a rHCIII hydrogel can improve cardiac function post-MI but that injecting more rHCIII (by increased concentration or more over time) can reduce its efficacy, thus highlighting the importance of investigating optimal treatment strategies of biomaterial therapy for MI.

Optimizing the host substrate environment for cardiac angiogenesis, arteriogenesis, and myogenesis

INTRODUCTION

The diseased host milieu, such as endothelial dysfunction (ED), decreased NO bioavailability, and ischemic/inflammatory post-MI environment, hamper the clinical success of existing cardiac regenerative therapies. Area covered: In this article, current strategies including pharmacological and nonpharmacological approaches for improving the diseased host milieu are reviewed. Specifically, the authors provide focus on: i) the mechanism of ED in patients with cardiovascular diseases, ii) the current results of ED improving strategies in pre-clinical and clinical studies, and iii) the use of biomaterials as a novel modulator in damaged post-MI environment. Expert opinion: Adjunct therapies which improve host endothelial function have demonstrated promising outcomes, potentially overcoming disappointing results of cell therapy in human studies. In the future, elucidation of the interactions between the host tissue and therapeutic agents, as well as downstream signaling pathways, will be the next challenges in enhancing regenerative therapy. More careful investigations are also required to establish these agents' safety and efficacy for wide usage in humans.