Soren Schenk

Monocyte Chemotactic Protein‐3 Is a Myocardial Mesenchymal Stem Cell Homing Factor

MSCs have received attention for their therapeutic potential in a number of disease states, including bone formation, diabetes, stem cell engraftment after marrow transplantation, graft‐versus‐host disease, and heart failure. Despite this diverse interest, the molecular signals regulating MSC trafficking to sites of injury are unclear. MSCs are known to transiently home to the freshly infarcted myocardium. To identify MSC homing factors, we determined chemokine expression pattern as a function of time after myocardial infarction (MI). We merged these profiles with chemokine receptors expressed on MSCs but not cardiac fibroblasts, which do not home after MI. This analysis identified monocyte chemotactic protein‐3 (MCP‐3) as a potential MSC homing factor. Overexpression of MCP‐3 1 month after MI restored MSC homing to the heart. After serial infusions of MSCs, cardiac function improved in MCP‐3‐expressing hearts (88.7%, p < .001) but not in control hearts (8.6%, p = .47). MSC engraftment was not associated with differentiation into cardiac myocytes. Rather, MSC engraftment appeared to result in recruitment of myofibroblasts and remodeling of the collagen matrix. These data indicate that MCP‐3 is an MSC homing factor; local overexpression of MCP‐3 recruits MSCs to sites of injured tissue and improves cardiac remodeling independent of cardiac myocyte regeneration.

Alloreactive T Cell Responses and Acute Rejection of Single Class II MHC-Disparate Heart Allografts Are under Strict Regulation by CD4+CD25+ T Cells

Skin but not vascularized cardiac allografts from B6.H-2bm12 mice are acutely rejected by C57BL/6 recipients in response to the single class II MHC disparity. The underlying mechanisms preventing acute rejection of B6.H-2bm12 heart allografts by C57BL/6 recipients were investigated. B6.H-2bm12 heart allografts induced low levels of alloreactive effector T cell priming in C57BL/6 recipients, and this priming was accompanied by low-level cellular infiltration into the allograft that quickly resolved. Recipients with long-term-surviving heart allografts were unable to reject B6.H-2bm12 skin allografts, suggesting potential down-regulatory mechanisms induced by the cardiac allografts. Depletion of CD25+ cells from C57BL/6 recipients resulted in 15-fold increases in alloreactive T cell priming and in acute rejection of B6.H-2bm12 heart grafts. Similarly, reconstitution of B6.Rag−/− recipients with wild-type C57BL/6 splenocytes resulted in acute rejection of B6.H-2bm12 heart grafts only if CD25+ cells were depleted. These results indicate that acute rejection of single class II MHC-disparate B6.H-2bm12 heart allografts by C57BL/6 recipients is inhibited by the emergence of CD25+ regulatory cells that restrict the clonal expansion of alloreactive T cells.

Effects of T Cell Frequency and Graft Size on Transplant Outcome in Mice

The features that determine whether graft-reactive T lymphocytes develop into effector cells capable of mediating organ destruction are not well understood. To investigate potential factors involved in this process, we first confirmed that female recipient mice acutely rejected minor Ag-disparate male skin, but not heart transplants. Despite this difference in outcome, heart and skin transplantation induced antidonor T cell responses of similar magnitude, specificity, and cytokine profile. The heart-graft-primed T cells transiently infiltrated the graft and ultimately induced the development of chronic transplant vasculopathy. Increasing the frequency of donor-reactive T cells by presensitization or by using TCR (CD8+ antimale)-transgenic recipients did not mediate acute rejection but accelerated the pace and severity of the vasculopathy. Surprisingly, decreasing the tissue mass of the donor heart by 50% resulted in acute rejection of these smaller grafts without increasing the frequency of antidonor effector T cells in the recipients. In complementary studies, placement of one or two male skin grafts on a single recipient did not affect the frequency or cytokine profile of the induced antimale T cell repertoire. Nonetheless, the recipients of single grafts acutely rejected the transplanted skin while the recipients of two skin grafts did not. These results provide new insight into the pathogenesis of transplant vasculopathy and provide an explanation for the difference in outcome between murine skin and heart transplants by highlighting the novel concept that the efficiency of transplant-reactive T cell immunity is heavily influenced by the tissue burden it encounters at the effector stage.

Off-pump mitral valve repair using the Coapsys device: a pilot study in a pacing-induced mitral regurgitation model

PURPOSE The purpose of this study was to evaluate the ability of the Myocor Coapsys device to restore leaflet apposition and valve competency off-pump in a canine model of functional mitral regurgitation (MR). DESCRIPTION The Coapsys device was surgically implanted in 10 dogs after MR induction by rapid ventricular pacing. The Coapsys consists of anterior and posterior epicardial pads connected by a subvalvular chord. The annular head of the posterior pad was positioned at the annular level to draw the posterior leaflet and annulus toward the anterior leaflet. Final device size was selected when MR was minimized or eliminated as assessed by color flow Doppler echocardiography. EVALUATION All implants were placed off-pump without atriotomy, and mean MR grade was reduced from 2.9 +/- 0.7 to 0.6 +/- 0.7 (p < 0.001) acutely. No hemodynamic compromise was noted. CONCLUSIONS The Coapsys device consistently and significantly reduced or eliminated functional MR acutely. Further study will be required to assess the chronic stability of the repair in this animal model.

Chronic hydrocephalus-induced changes in cerebral blood flow: mediation through cardiac effects

Decreased cerebral blood flow (CBF) in hydrocephalus is believed to be related to increased intracranial pressure (ICP), vascular compression as the result of enlarged ventricles, or impaired metabolic activity. Little attention has been given to the relationship between cardiac function and systemic blood flow in chronic hydrocephalus (CH). Using an experimental model of chronic obstructive hydrocephalus developed in our laboratory, we investigated the relationship between the duration and severity of hydrocephalus and cardiac output (CO), CBF, myocardial tissue perfusion (MTP), and peripheral blood flow (PBF). Blood flow measures were obtained using the microsphere injection method under controlled hemodynamic conditions in experimental CH (n = 23) and surgical control (n = 8) canines at baseline and at 2, 4, 8, 12, and 16 weeks. Cardiac output measures were made using the Swan–Ganz thermodilution method. Intracranial compliance (ICC) via cerebrospinal fluid (CSF) bolus removal and infusion, and oxygen delivery in CSF and prefrontal cortex (PFC) were also investigated. We observed an initial surgical effect relating to 30% CO reduction and ∼50%> decrease in CBF, MTP, and PBF in both groups 2 weeks postoperatively, which recovered in control animals but continued to decline further in CH animals at 16 weeks. Cerebral blood flow, which was positively correlated with CO (P = 0.028), showed no significant relationship with either CSF volume or pressure. Decreased CBF correlated with oxygen deprivation in PFC (P = 0.006). Cardiac output was inversely related with ventriculomegaly (P = 0.019), but did not correlate with ICP. Decreased CO corresponded to increased ICC, as measured by CSF infusion (P = 0.04). Our results suggest that CH may have more of an influence on CO and CBF in the chronic stage than in the early condition, which was dominated by surgical effect. The cause of this late deterioration of cardiac function in hydrocephalus is uncertain, but may reflect cardiac regulation secondary to physiologic response or brain injury. The relationship between cardiac function and CBF should be considered in the pathophysiology and clinical treatment of CH.

Dissociation between Vascular Endothelial Growth Factor Receptor-2 and Blood Vessel Density in the Caudate Nucleus after Chronic Hydrocephalus

Chronic hydrocephalus (CH) is characterized by the presence of ventricular enlargement, decreased cerebral blood flow (CBF), and brain tissue oxygen delivery. Although the underlying pathophysiological role of vascular endothelial growth factor (VEGF) is not clear, ischemic–hypoxic events in CH are known to trigger its release. Previously, we have shown increased VEGF receptor-2 (VEGFR-2) and blood vessel density (BVd) in the hippocampus after CH. We investigated changes in neuronal and glial VEGFR-2 density and BVd in the caudate nucleus in an experimental model of CH. Animals with CH were divided into short term (ST, 2 to 4 weeks) and long term (LT, 12 to 16 weeks) and were compared with surgical controls (SCs, 12 to 16 weeks). The cellular and BVds were estimated using immunohistochemical and stereological counting methods. Overall, percentage (%)VEGFR-2 neurons were approximately two times greater in CH (ST, LT) than in SC. By comparison, glial cell %VEGFR-2 was greater by 10% to 17% in ST and 4% to 11% lower in LT compared with that in SC. Blood vessel density was significantly lower in CH than in SC in the superficial caudate. Changes in cerebrospinal fluid ventricular volume and pressure, as well as in CBF did not correlate with either VEGFR-2 or BVd. These observed findings suggest that destructive forces may outweigh angiogenic forces and possibly show a disassociation between VEGFR-2 and BV expressions.

Reduction of mitral regurgitation using the coapsys device: A novel ex vivo method using excised recipients' hearts

The purpose of this study was to evaluate the ex vivo effects of the Coapsys device upon functional mitral regurgitation (MR) in human hearts. We used seven excised hearts from patients who underwent cardiac transplantation. All patients had functional MR of grade 2 or greater associated with dilated (n = 3) or ischemic (n = 4) cardiomyopathy. After the aortic valve was removed, the left ventricle was pressurized from the aorta with saline at a constant pressure. The degree of MR was then subjectively graded from the opened left atrium (from 0 to 4). The last three studies included volumetric measurements of MR. By tightening the device, the mean MR grade was reduced from 3.3 ± 0.8 to 1.1 ± 0.4 (p = 0.0002). In the quantitative analysis, mean regurgitation volume was reduced from 1,108 ± 1,134 ml/min to 236 ± 89 ml/min (p = not significant). The mitral annular septal-lateral dimension decreased from 2.0 ± 0.3 cm to 1.6 ± 0.5 (p = 0.043). The Coapsys device reduced functional MR in the ex vivo study using excised dilated hearts.

Mitral Valve Repair without Cardiopulmonary Bypass or Atriotomy Using the Coapsys Device: Device Design and Implantation Procedure in Canine Functional Mitral Regurgitation Model

BACKGROUND Myocor developed a unique system, the Coapsys annuloplasty system, to treat functional mitral regurgitation (MR) without cardiopulmonary bypass (CPB). This study was conducted to test the feasibility of the Coapsys implantation procedure in a canine functional MR model. METHODS Functional MR with heart failure was induced in 9 dogs by rapid ventricular pacing (230 beats/min for 30 +/- 4 days). The Coapsys device, which consists of anterior and posterior epicardial pads connected by a subvalvular chord, was then surgically implanted. Under epicardial echocardiographic guidance, we placed the Coapsys device across the left ventricular chamber using the delivery instrument and needle assembly. We sized the Coapsys device by drawing the posterior leaflet and annulus toward the anterior leaflet with the sizing instrument. Final device size was selected when MR was minimized or eliminated as assessed by 2-dimensional color Doppler echocardiography. RESULTS In all cases, we successfully implanted the Coapsys device without CPB or atriotomy. MR was reduced an average of 2 grades. No adverse events, such as hemodynamic compromise or structural valve damage, were noted. CONCLUSION Coapsys device implantation was feasible and safe on a beating canine heart. All accessory tools used for device implantation were found useful.

In vivo performance and biocompatibility of the MagScrew ventricular assist device

Currently available ventricular assist devices (VADs) have limitations in long-term durability and blood compatibility. We evaluated a prototype of a pulsatile MagScrew VAD for in vivo hemodynamic performance and biocompatibility. The device is composed of an actuator, blood pump housing, diaphragm, pusher plate, and bioprosthetic valves. Its protein-coated (“biolized”) blood-contacting surface inhibits clot formation. Forces between moving parts of the actuator are transmitted magnetically, eliminating a primary source of friction and wear. The pump fills passively and is highly preload sensitive. The device was implanted into three calves for 90, 10, and 57 days, respectively. No anticoagulants were given postoperatively. The device functioned without technical problems during the entire course of each experiment, with mean device flow ranging between 5.4 and 9.0 L/min. Autopsy of the first two calves revealed no sign of embolization and clean blood-contacting surfaces of the devices. The third experiment was complicated by a prosthetic valve endocarditis with infectious embolization, and a few small depositions were found in the pump. In conclusion, the MagScrew VAD has demonstrated a high level of performance and biocompatibility in three calves studied for 10–90 days. Vigorous development is in progress to bring this device to preclinical readiness and thus provide surgeons with the VAD of choice for permanent implantation.

Pitfalls in catheter-based interventions to treat paravalvular leaks

Paravalvular leaks of prosthetic heart valves can be observed at a rate as great as 1.4% leaks/patient-year. Surgical correction can be performed with low mortality in most instances of clinically relevant regurgitation or hemolysis. More recently, interventional cardiologic techniques are of growing interest. This report depicts 3 patients who required surgical treatment for interventional complications. Current challenges and indications for this evolving technology are discussed.