Therapeutic Efficacy of Cryopreserved, Allogeneic Extracellular Vesicles for Treatment of Acute Myocardial Infarction.

Extracellular vesicles (EV) that are derived from endothelial progenitor cells (EPC) have been determined to be a novel therapy for acute myocardial infarction, with a promise for immediate "off-the-shelf" delivery. Early experience suggests delivery of EVs from allogeneic sources is safe. Yet, clinical translation of this therapy requires assurances of both EV stability following cryopreservation and absence of an adverse immunologic response to EVs from allogeneic donors. Thus, more bioactivity studies on allogeneic EVs after cold storage are necessary to establish quality standards for its widespread clinical use. Thus, in this study, we aimed to demonstrate the safety and efficacy in delivering cryopreserved EVs in allogeneic recipients as a therapy for acute myocardial infarction.In this present study, we have analyzed the cardioprotective effects of allogeneic EPC-derived EVs after storage at -80°C for 2 months, using a shear-thinning gel (STG) as an in vivo delivery vehicle. EV size, proteome, and nucleic acid cargo were observed to remain steady through extended cryopreservation via nanoparticle tracking analysis, mass spectrometry, and nanodrop analysis, respectively. Fresh and previously frozen EVs in STG were delivered intramyocardially in a rat model of myocardial infarction (MI), with both showing improvements in contractility, angiogenesis, and scar thickness in comparison to phosphate-buffered saline (PBS) and STG controls at 4 weeks post-MI. Pathologic analyses and flow cytometry revealed minimal inflammatory and immune upregulation upon exposure of tissue to EVs pooled from allogeneic donor cells.Allogeneic EPC-EVs have been known to elicit minimal immune activity and retain therapeutic efficacy after at least 2 months of cryopreservation in a post-MI model.

Delayed delivery of endothelial progenitor cell-derived extracellular vesicles via shear thinning gel improves postinfarct hemodynamics.

BACKGROUND: Extracellular vesicles (EVs) are promising therapeutics for cardiovascular disease, but poorly-timed delivery might hinder efficacy. We characterized the time-dependent response to endothelial progenitor cell (EPC)-EVs within an injectable shear-thinning hydrogel (STG+EV) post-myocardial infarction (MI) to identify when an optimal response is achieved. METHODS: The angiogenic effects of prolonged hypoxia on cell response to EPC-EV therapy and EV uptake affinity were tested in vitro. A rat model of acute MI via left anterior descending artery ligation was created and STG+EV was delivered via intramyocardial injections into the infarct border zone at time points corresponding to phases of post-MI inflammation: 0 hours (immediate), 3 hours (acute inflammation), 4 days (proliferative), and 2 weeks (fibrosis). Hemodynamics 4 weeks post-treatment were compared across treatment and control groups (phosphate buffered saline [PBS], shear-thinning gel). Scar thickness and ventricular diameter were assessed histologically. The primary hemodynamic end point was end systolic elastance. The secondary end point was scar thickness. RESULTS: EPC-EVs incubated with chronically versus acutely hypoxic human umbilical vein endothelial cells resulted in a 2.56 ± 0.53 versus 1.65 ± 0.15-fold increase (P = .05) in a number of vascular meshes and higher uptake of EVs over 14 hours. End systolic elastance improved with STG+EV therapy at 4 days (0.54 ± 0.08) versus PBS or shear-thinning gel (0.26 ± 0.03 [P = .02]; 0.23 ± 0.02 [P = .01]). Preservation of ventricular diameter (6.20 ± 0.73 mm vs 8.58 ± 0.38 mm [P = .04]; 9.13 ± 0.25 mm [P = .01]) and scar thickness (0.89 ± 0.05 mm vs 0.62 ± 0.03 mm [P < .0001] and 0.58 ± 0.05 mm [P < .0001]) was significantly greater at 4 days, compared wit PBS and shear-thinning gel controls. CONCLUSIONS: Delivery of STG+EV 4 days post-MI improved left ventricular contractility and preserved global ventricular geometry, compared with controls and immediate therapy post-MI. These findings suggest other cell-derived therapies can be optimized by strategic timing of therapeutic intervention.

Relationship Between Change in Heart Transplant Volume and Outcomes: A National Analysis.

INTRODUCTION: Although volume-outcome relationships in transplantation have been well-defined, the effects of large changes in center volume are less well understood. The purpose of the current study was to examine the impact of changes in center volume on outcomes after heart transplantation. METHODS: Retrospective analysis was performed of adult patients undergoing heart transplant between 2000 and 2017 identified in the United Network for Organ Sharing database. Exclusions included annual volume <10. Patients were grouped according to percentage change in center volume from the previous year. Multivariable Cox regression models were adjusted for the significant preoperative variance identified on univariate analyses. RESULTS: Of the 29,851 transplants during the study period, 64% were at centers with stable volume (±25% annual change), whereas 10% were performed at contracting (-25% change or more) and 26% were performed at growing (+25% change or more) centers. Average volume was lower with contracting centers compared with stable or growing programs (21 vs 36, P< .001). Thirty-day mortality was greater in decreasing centers (6% vs 4%, P < .001), with more acute rejection treatments at 1y (27% vs 24% P < .001). The adjusted risk of mortality among contracting centers was 1.25 ([1.07-1.46], P= .004), whereas growing centers had unaffected risk (0.90 [0.79-1.02], P= .103). Causes of death were similar between groups. CONCLUSIONS: Rapid growth of transplant center volume has occurred at select centers in the United States without decrement in programmatic outcomes. Decreasing center volume has been associated with poorer outcomes, although the causative nature of this relationship requires further investigation.

Better With Time: An Economic Assessment of Long-Term Mechanical Circulatory Support in a Population Surviving at Least 1 Year with a Left Ventricular Assist Device.

This study aims to identify the major components of left ventricular assist device (LVAD)-related costs in a population on long-term mechanical circulatory support to gain insight into opportunities for improvements in quality, safety, and efficiency of care for end-stage heart failure patients. This was a single institution, retrospective cost analysis of patients who received a Heartmate II or HeartWare LVAD between November 2005 and October 2015. Payments for hospitalization for device implantation and subsequent readmissions were represented as the institution's 2015 Medicare reimbursement rate. The incidence, average Medicare reimbursement, and length of stay of readmissions were analyzed for the first year postimplant. A full year of LVAD-related hospitalizations in patients surviving ≥12 months, has a median Medicare reimbursement of $247,208. The most common complications related to ventricular assist devices were gastrointestinal bleeding, driveline infection, stroke, and pump thrombosis. Over 90% of total costs were incurred during the initial hospitalization. Seventy-five percent of first-time readmissions occurred within the first 4 months post discharge. Intensive care unit costs accounted for the single largest cost category during readmissions for all of the 4 most common complications. The trends demonstrated suggest that longer lengths of LVAD support in appropriately selected patients results in progressively decreasing cost-per-month up to 12 months, given the large upfront cost of device implantation and relatively modest additional costs of readmissions. This analysis emphasizes the importance of devices with improved complication profiles and clinical protocols to reduce unnecessary intensive care unit stays to increase the cost effectiveness of long-term ventricular assist device therapy.

Transplant Volume Is Associated With Graft Acceptance Threshold and Center Resource Availability.

BACKGROUND: Heart transplant volume varies significantly among centers. We hypothesized that centers where the transplant team routinely accepts organs previously declined by other centers and where operating room availability is unrestricted have higher transplant volumes. METHODS AND RESULTS: We used the potential transplant recipient sequence number in the United Network for Organ Sharing database as a surrogate for graft acceptance threshold and the number of transplantations occurring on weekends and 8 major holidays as a marker of center resource availability. Centers were classified as low-, medium-, or high-volume if the average annual number of transplants were, respectively, <10, 10-30, or >30 over a 10-year period. From July 12, 2006, to December 31, 2015, 19,054 transplants were performed by 142 centers. There were 59 low-volume centers, 69 medium-volume centers, and 14 high-volume centers with median potential transplant recipient sequence numbers for transplanted candidates of 7 (interquartile range 3-11), 7 (5-10), and 15 (7-40), respectively (P = .002). The median proportion of off-hours transplantations performed by medium-volume centers was 28% (25%-31%) compared with 32% (29%-33%) by high-volume centers (P = .009). Five-year survival was equivalent among all centers (P = .053). CONCLUSIONS: Transplants for candidates with high sequence numbers and unrestricted operating room availability are associated with increased center volume without sacrificing post-transplantation survival.

Delivery of progenitor cells with injectable shear-thinning hydrogel maintains geometry and normalizes strain to stabilize cardiac function after ischemia.

OBJECTIVES: The ventricle undergoes adverse remodeling after myocardial infarction, resulting in abnormal biomechanics and decreased function. We hypothesize that tissue-engineered therapy could minimize postischemic remodeling through mechanical stress reduction and retention of tensile myocardial properties due to improved endothelial progenitor cell retention and intrinsic biomechanical properties of the hyaluronic acid shear-thinning gel. METHODS: Endothelial progenitor cells were harvested from adult Wistar rats and resuspended in shear-thinning gel. The constructs were injected at the border zone of ischemic rat myocardium in an acute model of myocardial infarction. Myocardial remodeling, tensile properties, and hemodynamic function were analyzed: control (phosphate-buffered saline), endothelial progenitor cells, shear-thinning gel, and shear-thinning gel + endothelial progenitor cells. Novel high-resolution, high-sensitivity ultrasound with speckle tracking allowed for global strain analysis. Uniaxial testing assessed tensile biomechanical properties. RESULTS: Shear-thinning gel + endothelial progenitor cell injection significantly increased engraftment and retention of the endothelial progenitor cells within the myocardium compared with endothelial progenitor cells alone. With the use of strain echocardiography, a significant improvement in left ventricular ejection fraction was noted in the shear-thinning gel + endothelial progenitor cell cohort compared with control (69.5% ± 10.8% vs 40.1% ± 4.6%, P = .04). A significant normalization of myocardial longitudinal displacement with subsequent stabilization of myocardial velocity with shear-thinning gel + endothelial progenitor cell therapy compared with control was also evident (0.84 + 0.3 cm/s vs 0.11 ± 0.01 cm/s, P = .03). A significantly positive and higher myocardial strain was observed in shear-thinning gel + endothelial progenitor cell (4.5% ± 0.45%) compared with shear-thinning gel (3.7% ± 0.24%), endothelial progenitor cell (3.5% ± 0.97%), and control (8.6% ± 0.3%, P = .05). A resultant reduction in dynamic stiffness was noted in the shear-thinning gel + endothelial progenitor cell cohort. CONCLUSIONS: This novel injectable shear-thinning hyaluronic acid hydrogel demonstrates stabilization of border zone myocardium with reduction in adverse myocardial remodeling and preservation of myocardial biomechanics. The cellular construct provides a normalization of strain measurements and reduces left ventricular dilatation, thus resulting in improvement of left ventricular function.

Injectable Supramolecular Hydrogel/Microgel Composites for Therapeutic Delivery.

Shear-thinning hydrogels are useful for biomedical applications, from 3D bioprinting to injectable biomaterials. Although they have the appropriate properties for injection, it may be advantageous to decouple injectability from the controlled release of encapsulated therapeutics. Toward this, composites of hydrogels and encapsulated microgels are introduced with microgels that are fabricated via microfluidics. The microgel cross-linker controls degradation and entrapped molecule release, and the concentration of microgels alters composite hydrogel rheological properties. For the treatment of myocardial infarction (MI), interleukin-10 (IL-10) is encapsulated in microgels and released from composites. In a rat model of MI, composites with IL-10 reduce macrophage density after 1 week and improve scar thickness, ejection fraction, cardiac output, and the size of vascular structures after 4 weeks when compared to saline injection. Improvements are also observed with the composite without IL-10 over saline, emphasizing the role of injectable hydrogels alone on tissue repair.

Injectable and protease-degradable hydrogel for siRNA sequestration and triggered delivery to the heart.

Injectable hydrogels have significant therapeutic potential for treatment of myocardial infarction (MI) through tissue bulking and local drug delivery, including the delivery of small interfering RNAs (siRNAs). As siRNA targets are identified as potential treatments for MI, hydrogels may bolster efficacy through local and sustained release. Here, we designed an injectable hydrogel to respond to local upregulation in proteolytic activity after MI to erode and release siRNA against MMP2 (siMMP2), a target implicated in deleterious remodeling. Specifically, hyaluronic acid (HA) was modified with hydrazides or aldehydes and mixed to form shear-thinning and self-healing hydrogels through dynamic hydrazone bonds and with peptide crosslinkers that degrade in response to protease activity. HA was further modified with ß-cyclodextrin to sequester cholesterol-modified siRNA, limiting passive diffusion. Hydrogels eroded in response to proteases and released active siRNA that knocked down MMP2 in primary cardiac fibroblasts. In a rat model of MI, hydrogels delivering siMMP2 attenuated hydrogel erosion by ~46% at 4 weeks when compared to hydrogels delivering control siRNA, ultimately improving myocardial thickness in the infarct. Delivery of the siMMP2 hydrogel led to significant functional improvements, including increased ejection fraction (27%, 66%), stroke volume (32%, 120%), and cardiac output (20%, 128%) when compared to controls (% increase versus hydrogels with control siRNA, % increase versus saline injection alone). This report demonstrates the utility of biomaterial-based RNA delivery systems for cardiac applications.

Injectable Granular Hydrogels with Multifunctional Properties for Biomedical Applications.

Injectable hydrogels are useful for numerous biomedical applications, such as to introduce therapeutics into tissues or for 3D printing. To expand the complexity of available injectable hydrogels, shear-thinning and self-healing granular hydrogels are developed from microgels that interact via guest-host chemistry. The microgel properties (e.g., degradation, molecule release) are tailored through their crosslinking chemistry, including degradation in response to proteases. When microgels of varied formulations are mixed, complex release and degradation behaviors are observed, including after injection to permit cellular invasion.