Myocardial drug distribution generated from local epicardial application: potential impact of cardiac capillary perfusion in a swine model using epinephrine

Immune-modulatory alginate protects mesenchymal stem cells for sustained delivery of reparative factors to ischemic myocardium

Paracrine factors secreted by mesenchymal stem cells (MSCs) have been previously shown to improve cardiac function following acute myocardial infarction (MI). However, cell therapy activates the innate immune response, leading to the rapid elimination of transplanted cells and only short-term therapeutic delivery. Herein, we describe a new strategy to deliver sustained paracrine-mediated MSC therapy to ischemic myocardium. Using an immune evasive, small molecule modified alginate, we encapsulated rat MSC cells in a core-shell hydrogel capsule and implanted them in the pericardial sac of post-MI rats. Encapsulated cells allowed diffusion of reparative paracrine factors at levels similar to non-encapsulated cells in vitro. Encapsulation enabled sustained cell survival with localization over the heart for 2 weeks. The effect of the experimental group on ventricular function and fibrosis was compared with blank (cell free) capsules and unencapsulated MSCs injected into infarcted myocardium. MSC capsules improved post-MI ventricular function ∼2.5× greater than MSC injection. After 4 weeks, post-MI fibrosis was reduced ∼2/3 with MSC capsules, but unchanged with MSC injection. MSC encapsulation with alginate core-shell capsules sustains cell survival and potentiates efficacy of therapy.

Multiscale Experimental and Computational Modeling Approaches to Characterize Therapy Delivery to the Heart from an Implantable Epicardial Biomaterial Reservoir

Delivery of therapeutic-laden biomaterials to the epicardial surface of the heart presents a promising method of treating a variety of diseased conditions by offering targeted, localized release with limited systemic recirculation and enhanced myocardial tissue uptake. A vast range of biomaterials and therapeutic agents using this approach been investigated. However, the fundamental factors that govern transport of the drug molecules from the biomaterials to the tissue are not well understood. Here, the transport of a drug analog from a biomaterial reservoir to the epicardial surface is characterized using experimental techniques and microscale modeling. Using the experimentally determined parameters, a multiscale model of transport is developed. The model is then used to study the effect of important design parameters such as loading conditions, biomaterial geometry, and orientation relative to the cardiac fibers on drug delivery to the myocardium. The simulations highlight the significance of the cardiac fiber anisotropy as a crucial factor in governing drug distribution on the epicardial surface and limiting factor for penetration into the myocardium. The multiscale model can be useful for rapid iteration of different device concepts and for determination of designs for epicardial drug delivery that may be optimal and most promising for the ultimate therapeutic goal.

[Establishment of a rabbit model of small diameter vascular graft replacement]

OBJECTIVE

To establish an rabbit model that mimics the hemodynamics of the bypass graft after coronary artery bypass surgery.

METHODS

Sixteen New Zealand rabbits were randomly divided into two groups for abdominal aortic artery replacement using a 3-cm-long ePTFE graft with an inner diameter 4 mm through an incision at 1/3 from the middle to the lower part of the abdomen (group A) or in the lower abdomen (group B). The general conditions of the rabbits, operative time, number of collateral vessels that needed to be ligated, rate of massive intraoperative bleeding, fluctuation of vascular anastomosis after surgery, patency rate of the graft on day 7 after the operation were compared between the two groups.

RESULTS

The two groups of rabbits had similar body weight, diameter of the abdominal aortic artery, intraoperative bleeding rate and occlusion rate of the vascular graft at 7 days after the procedure. The operative time was longer in group A, but the difference was not statistically significant. In group A, the number of the vascular branches that needed to be ligated was smaller and the rate normal femoral artery pulsation was higher than those in group B.

CONCLUSION

It is feasible to establish models of small diameter vascular graft replacement in rabbits, and the patency rate of the graft can be monitored by observation of the general condition and ultrasound examination of the rabbits.

Delivery of drugs, growth factors, genes and stem cells via intrapericardial, epicardial and intramyocardial routes for sustained local targeted therapy of myocardial disease

INTRODUCTION

Local myocardial delivery (LMD) of therapeutic agents is a promising strategy that aims to treat various myocardial pathologies. It is designed to deliver agents directly to the myocardium and minimize their extracardiac concentrations and side effects. LMD aims to enhance outcomes of existing therapies by broadening their therapeutic window and to utilize new agents that could not be otherwise be implemented systemically. Areas covered: This article provides a historical overview of six decades LMD evolution in terms of the approaches, including intrapericardial, epicardial, and intramyocardial delivery, and the wide array of classes of agents used to treat myocardial pathologies. We examines delivery of pharmaceutical compounds, targeted gene transfection and cell implantation techniques to produce therapeutic effects locally. We outline therapeutic indications, successes and failures as well as technical approaches for LMD. Expert opinion: While LMD is more complicated than conventional oral or intravenous administration, given recent advances in interventional cardiology, it is safe and may provide better therapeutic outcomes. LMD is complex as many factors impact pharmacokinetics and biologic result. The choice between routes of LMD is largely driven not only by the myocardial pathology but also by the nature and physicochemical properties of the therapeutic agents.

A four-compartment PBPK heart model accounting for cardiac metabolism - model development and application

In the field of cardiac drug efficacy and safety assessment, information on drug concentration in heart tissue is desirable. Because measuring drug concentrations in human cardiac tissue is challenging in healthy volunteers, mathematical models are used to cope with such limitations. With a goal of predicting drug concentration in cardiac tissue, we have developed a whole-body PBPK model consisting of seventeen perfusion-limited compartments. The proposed PBPK heart model consisted of four compartments: the epicardium, midmyocardium, endocardium, and pericardial fluid, and accounted for cardiac metabolism using CYP450. The model was written in R. The plasma:tissues partition coefficients (Kp) were calculated in Simcyp Simulator. The model was fitted to the concentrations of amitriptyline in plasma and the heart. The estimated parameters were as follows: 0.80 for the absorption rate [h-1], 52.6 for Kprest, 0.01 for the blood flow through the pericardial fluid [L/h], and 0.78 for the P-parameter describing the diffusion between the pericardial fluid and epicardium [L/h]. The total cardiac clearance of amitriptyline was calculated as 0.316 L/h. Although the model needs further improvement, the results support its feasibility, and it is a first attempt to provide an active drug concentration in various locations within heart tissue using a PBPK approach.