Percutaneous cell delivery into the heart using hydrogels polymerizing in situ

Abstract

Heart disease is the leading cause of death in the US. Following an acute myocardial infarction, a fibrous, noncontractile scar develops, and results in congestive heart failure in more than 500,000 patients in the US each year. Muscle regeneration and the induction of new vascular growth to treat ischemic disorders of the heart can have significant therapeutic implications. Early studies in patients with chronic ischemic systolic left ventricular dysfunction (SLVD) using skeletal myoblasts or bone marrow-derived cells report improvement in left ventricular ejection function (LVEF) and clinical status, without notable safety issues. Nonetheless, the efficacy of cell transfer for cardiovascular disease is not established, in part due to a lack of control over cell retention, survival, and function following delivery. We studied the use of biocompatible hydrogels polymerizable in situ as a cell delivery vehicle, to improve cell retention, survival, and function following delivery into the ischemic myocardium. The study was conducted using human bone marrow-derived mesenchymal stem cells and fibrin glue, but the methods are applicable to any human stem cells (adult or embryonic) and a wide range of hydrogels. We first evaluated the utility of several commercially available percutaneous catheters for delivery of viscous cell/hydrogel suspensions. Next we characterized the polymerization kinetics of fibrin glue solutions to define the ranges of concentrations compatible with catheter delivery. We then demonstrate the in vivo effectiveness of this preparation and its ability to increase cell retention and survival in a nude rat model of myocardial infarction.

Figure 1

Catheter-based delivery of actively polymerizing compounds is limited by increasing resistance to flow over time and requires a balance between overly rapid (clogged catheter) and overly slow (loss of cell product) kinetics.

Figure 2

(a) Fibrinogen solutions show a nonlinear increase in viscosity with increasing weight percentage. (b) By maintaining fibrinogen weight percentages below 5% w/v and thrombin concentrations under 20 U/ml, polymerization rates can be controlled to allow adequate time for percutaneous delivery. The dotted line indicates the operational upper viscosity limit of 200 cP.

Figure 3

(a) MSCs cultured in fibrin gels maintained excellent viability over 72 h of culture. (b) Live-dead stain of MSCs 72 h after culture in a fibrin gel (living cells stain green, dead cells stain red, scale bar: 500 μm). (c, d) SEM of a 2% (w/v) fibrinogen gel polymerized with 20 U/ml of thrombin showing a heterogenous structure with pore sizes in the 20–40 μm range.

Figure 4

(a) Intramyocardial delivery of MSCs suspended in fibrin glue results in gross retention of hydrogel (b, scale bar: 10 mm) and noticeable infarct thickening (c, scale bar: 5 mm) 10 days after infarction and injection. (d) Trichrome staining of a left ventricular cross section demonstrates intramural presence of injectate (scale bar: 500 μm). (e) Quantification of iridium-labeled MSCs confirms a significant increase in local cardiac retention as well as prevention of end organ redistribution when MSCs are delivered in fibrin glue (black bars) compared to saline (white bars).