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Biomedical subjects

Richard B Thompson

Publications and source records attributed to Richard B Thompson.

34 records · Page 2Linked to original sources
PubMed2004

Gene delivery to aortocoronary saphenous vein grafts in a large animal model of intimal hyperplasia.

OBJECTIVE: More than 50% of aortocoronary saphenous vein grafts are occluded 10 years after surgery. Intimal hyperplasia is an initial, critical step in the progression toward occlusion. To date, no clinically relevant large animal models of aortocoronary saphenous vein graft intimal hyperplasia have been fully characterized. Gene therapy holds promise as a novel treatment for aortocoronary saphenous vein graft intimal hyperplasia. The 2 objectives of this study are to characterize a canine model of aortocoronary saphenous vein graft intimal hyperplasia and to demonstrate that ex vivo gene delivery is possible in these grafts using adenoviral vectors. METHODS: Ten dogs underwent aortocoronary bypass grafting using saphenous veins. Six dogs underwent serial arteriograms to monitor graft patency. On postoperative day 90, the dogs were killed and their grafted and nongrafted saphenous veins were studied histologically. Four dogs underwent the same procedure, but their saphenous veins were treated with 1 x 10(12) total viral particles of a replication-deficient, recombinant adenovirus containing beta-galactosidase (n = 2) or the beta-adrenergic receptor kinase carboxyl terminus (n = 2). These animals were killed on postoperative day 7 for determination of transgene expression. RESULTS: All grafts were demonstrated patent by arteriogram before the animals were killed. The mean intimal area of the saphenous vein grafts was increased when compared with that of the nongrafted saphenous veins (2.83 mm(2) vs 0.09 mm(2), P <.0008). Adenoviral-treated saphenous vein grafts demonstrated positive transgene expression either by X-gal staining (beta-galactosidase) or Northern analysis (beta-adrenergic receptor kinase carboxyl terminus). CONCLUSION: This study characterizes a clinically relevant canine model of aortocoronary saphenous vein graft intimal hyperplasia. In addition, it demonstrates that adenoviral vectors can be delivered ex vivo to the saphenous vein graft vessel wall at subphysiologic distension pressures. This model may be used in future studies to manipulate molecular targets critical in aortocoronary saphenous vein graft intimal hyperplasia.

Animals↗
PubMed2004

Video-assisted thoracoscopic transplantation of myoblasts into the heart.

PURPOSE: Currently, cells are transplanted into injured myocardium either through thoracotomy for open surgical delivery or through catheterization for endoventricular or intracoronary delivery; both methods have limitations. Open surgical delivery limits the potential patient population, whereas catheter-based delivery limits the ability to visualize the injection site and confirm delivery of the cells to the appropriate region. In this study, we examine the feasibility of cell transplantation into myocardium using a minimally invasive thoracoscopic approach. DESCRIPTION: Seven swine underwent thoracoscopic cell transplantation. Using a prototype injection device, approximately 10 million myoblasts were injected into the anterior, lateral, posterior, and apical regions of myocardium. Animals were recovered up to 7 days, and after euthanasia, hearts were explanted for histology. EVALUATION: All seven swine had successful delivery of myoblasts into the defined injection sites, as confirmed by analysis of an operative video, magnetic resonance imaging of iron-oxide-labeled cells, and histologic examination. CONCLUSIONS: Thoracoscopic cellular cardiomyoplasty is feasible and allows the surgeon the benefits of direct visualization of the cell injection while minimizing morbidity associated with open cell delivery.

Animals↗
PubMed2004

Gene therapy for heart failure.

Despite our continued advances in the management of coronary artery disease, there have been no significant reductions in the morbidity or mortality related to end-stage heart failure. The syndrome of heart failure represents a common endpoint for several disease processes, however, at the molecular level there are certain biochemical similarities common to all failing myocardium. Targeting these derangements with gene therapy represents a promising option in the treatment of heart failure. In this review, we will discuss the common biochemical changes that occur in the failing heart, novel therapeutic targets, including the beta-adrenergic receptor system and intracellular calcium regulation, and the vectors and transfer methodology responsible for delivering these transgenes to the myocardium.

Animals↗
PubMed2003

Real-time determination of picomolar free Cu(II) in seawater using a fluorescence-based fiber optic biosensor.

We report real-time, in situ determination of free copper ion at picomolar levels in seawater using a fluorescence-based fiber optic biosensor. The sensor transducer is a protein molecule, site-specifically labeled with a fluorophore that is attached to the distal end of an optical fiber, which binds free Cu(II) with high affinity and selectivity. The transducer reports the metal's concentration as a change in fluorescence intensity or lifetime, using a frequency domain approach. The transducer's response time is diffusion-limited, with a typical measurement requiring 30 s. The sensor demonstrates a detection limit of 0.1 pM free Cu(II) in a seawater model. Accuracy and precision of the sensor were at least comparable to cathodic ligand exchange/adsorptive cathodic stripping voltammetry. Measurements of tidal flushing of a copper-contaminated inlet are shown.

Biosensing Techniques↗
PubMed2003

Comparison of intracardiac cell transplantation: autologous skeletal myoblasts versus bone marrow cells.

BACKGROUND: Multiple cell types are being proposed for cardiac repair, but side-by-side comparisons are lacking. We tested the hypothesis that intracardiac transplantation of autologous bone marrow- or skeletal muscle-derived progenitor cells improve regional heart function to a similar degree. METHODS AND RESULTS: Thirty-nine New Zealand White rabbits underwent cryoinjury of the left ventricle and simultaneous hind limb bone marrow aspiration or soleus muscle biopsy. Both muscle and bone marrow cells were expanded in vitro. After 2 weeks, 10(8) skeletal muscle (SM group) or bone marrow-derived progenitor cells (BM group) were injected into the cryoinjured region (SM: n=12; BM: n=8). Medium alone was injected into the remaining animals (Control: n=16). Regional systolic function was measured using micromanometry and sonomicrometry at baseline, before, and 4 weeks after cell injection. Cell treatment resulted in a similar degree of improvement in a derivative of stroke work in the SM and BM groups (P=0.0026 and P=0.0085 versus Control, respectively). No significant difference was seen between BM and SM groups (P=0.9). On histology, engrafted cells were found in all of the cell treated animals. Injected myoblasts formed myotubes or muscle cells throughout the scar that expressed slow and fast myosin heavy chain. A subset of bone marrow cells differentiated toward a myogenic phenotype, as indicated by expression of desmin and alpha-sarcomeric actin in the engrafted areas. CONCLUSIONS: Transplantation and myogenic differentiation of bone marrow-derived progenitor cells increased regional systolic heart function after myocardial injury to a similar degree as skeletal myoblasts.

Animals↗
PubMed2003

Serial cardiac magnetic resonance imaging of injected mesenchymal stem cells.

BACKGROUND: Delivery and tracking of endomyocardial stem cells are limited by the inability to image transplanted cells noninvasively in the beating heart. We hypothesized that mesenchymal stem cells (MSCs) could be labeled with a iron fluorophore particle (IFP) to provide MRI contrast in vivo to assess immediate and long-term localization. METHODS AND RESULTS: MSCs were isolated from swine. Short-term incubation of MSCs with IFP resulted in dose-dependent and efficient labeling. Labeled cells remained viable for multiple passages and retained in vitro proliferation and differentiation capacity. Labeled MSCs (10(4) to 10(6) cells/150 microL) were injected percutaneously into normal and freshly infarcted myocardium in swine. One, 3, and 1 animals underwent serial cardiac MRI (1.5T) for 4, 8, and 21 days, respectively. MRI contrast properties were measured both in vivo and in vitro for cells embedded in agar. Injection sites containing as few as 10(5) MSCs could be detected and contained intact IFP-bearing MSCs on histology. CONCLUSIONS: IFP labeling of MSCs imparts useful MRI contrast, enabling ready detection in the beating heart on a conventional cardiac MR scanner after transplantation into normal and infarcted myocardium. The dual-labeled MSCs can be identified at locations corresponding to injection sites, both ex vivo using fluorescence microscopy and in vivo using susceptibility contrast on MRI. This technology may permit effective in vivo study of stem cell retention, engraftment, and migration.

Animals↗
PubMed2003

Fast measurement of intracardiac pressure differences with 2D breath-hold phase-contrast MRI.

Intracardiovascular blood pressure differences can be derived from velocity images acquired with phase-contrast (PC) MRI by evaluating the Navier-Stokes equations. Pressure differences within a slice of interest can be calculated using only the in-plane velocity components from that slice. This rapid exam is proposed as an alternative to the lengthy 3D velocity imaging exams. Despite their good spatial coverage, the 3D exams are prone to artifacts and errors from respiratory motion and insufficient temporal resolution, and are unattractive in the clinical setting due to their excessive scan times (>10 min of free breathing). The proposed single-slice approach requires only one or two breath-holds of acquisition time, and the velocity data can be processed for the calculation of pressure differences online with immediate feedback. The impact of reducing the pressure difference calculation to two dimensions is quantified by comparison with 3D data sets for the case of blood flow within the cardiac chambers. The calculated pressure differences are validated using high-fidelity pressure transducers both in a pulsatile flow phantom and in vivo in a dog model. There was excellent agreement between the transducer and PC-MRI results in all of the studies.

Animals↗
PubMed2003

Real-time volumetric flow measurements with complex-difference MRI.

Blood flow in large vessels can be noninvasively evaluated with phase-contrast (PC) MRI by encoding the spin velocity to the image phase. Conventional phase-difference processing of the flow-encoded image data yields velocity images. Complex-difference processing is an alternative to phase-difference methods, and has the advantage of eliminating signal from stationary spins. In this study, two acquisitions with differential flow encoding are subtracted to yield a single projection that contains signal from only those spins moving in the direction of the flow-encoding gradients. The increase in acquisition efficiency allows real-time flow imaging with a temporal window as short as two acquisition lengths (60 ms). Validation of the complex-difference method by comparison with conventional gated-segmented PC-MRI in a flow phantom yielded a correlation of r > 0.99. Peak arterial flow rates in the popliteal artery and desending aorta measured in vivo with the complex-difference method were 0.92 +/- 0.06 of the values measured with conventional PC imaging. Real-time in vivo volumetric flow imaging of transient flow events is also presented.

Aorta, Abdominal↗
PubMed2003

The effects of acute afterload change on systolic ventricular function in conscious dogs with normal vs. failing hearts.

BACKGROUND: To date, no data exist on the linearity and, therefore, the usefulness of the preload recruitable stroke work (PRSW) and end-systolic pressure-volume (ESPVR) relationships during acute afterload changes in heart failure. AIMS: Our aim was, therefore, to characterize both relationships in a model of ventricular pacing induced heart failure at baseline and during acute changes in afterload. METHODS: Dynamic left ventricular volume and transmural pressure were measured in 10 conscious dogs using sonomicrometry and micromanometry under control conditions and during heart failure produced by 3 weeks of rapid right ventricular pacing. Afterload was varied from baseline with intravenous infusions of nitroprusside and phenylephrine. Left ventricular function was assessed using the PRSW and ESPVR relationships. RESULTS: Cardiac output demonstrated a linear inverse relationship with afterload in both normal and failing hearts (r2>0.5, P<0.001) with failure producing a parallel, downward shift of the afterload (x) vs. cardiac output (y) relationship (P<0.01). Yet, afterload variation did not affect PRSW or ESPVR relationships in either normal or failing hearts (r2<0.12, P>0.05). CONCLUSION: Thus, the PRSW and ESPVR relationships are insensitive to acute afterload changes in both failing and normal hearts, and the failing left ventricle is no more afterload-sensitive than the normal heart.

Animals↗
PubMed2003

A novel protective effect of erythropoietin in the infarcted heart.

Erythropoietin (EPO) has been shown to protect neurons from ischemic stroke, but can also increase thrombotic events and mortality rates in patients with ischemic heart disease. We reasoned that benefits of EPO might be offset by increases in hematocrit and evaluated the direct effects of EPO in the ischemic heart. We show that preconditioning with EPO protects H9c2 myoblasts in vitro and cardiomyocytes in vivo against ischemic injury. EPO treatment leads to significantly improved cardiac function following myocardial infarction. This protection is associated with mitigation of myocyte apoptosis, translating into more viable myocardium and less ventricular dysfunction. EPO-mediated myocyte survival appears to involve Akt activation. Importantly, cardioprotective effects of EPO were seen without an increase in hematocrit (eliminating oxygen delivery as an etiologic factor in myocyte survival and function), demonstrating that EPO can directly protect the ischemic and infarcted heart.

Animals↗
PubMed2003

Improved efficacy of stem cell labeling for magnetic resonance imaging studies by the use of cationic liposomes.

Labeling stem cells with FDA-approved superparamagnetic iron oxide particles makes it possible to track cells in vivo with magnetic resonance imaging (MRI), but high intracellular levels of iron can cause free radical formation and cytotoxicity. We hypothesized that the use of cationic liposomes would increase labeling efficiency without toxic effects. Rabbit skeletal myoblasts were labeled with iron oxide by: 1) uptake of iron oxide incorporated into cationic transfection liposomes (group I) or 2) customary endocytosis (group II). In both groups, cell proliferation and differentiation were measured and toxicity was assayed using trypan blue and ratio fluorescence microscopy with BODIPY 581/591 C11. The effects of the intracellular iron oxide on magnetic resonance image intensities were assessed in vitro and in vivo. Both methods resulted in uptake of iron intracellularly, yielding contrast-inducing properties on MRI images. In group II, however, incubation with iron oxide at high concentrations required for endocytosis caused generation of free radicals, a decrease in proliferation, and cell death. Cytotoxic effects in the remaining cells were still visible 24 h after incubation. Conversely, in group I, sufficient intracellular uptake for detection in vivo by MRI could be achieved at 100-fold lower concentrations of iron oxide, which resulted in a high percentage of labeled cells, high retention of the label, and no cytotoxic effects even after stressing the cells with a hypoxia-reoxygenation insult. The use of cationic liposomes for iron oxide stem cell labeling increases labeling efficiency approximately 100-fold without toxic effects. This technique results in high-contrast-inducing properties on MRI images both in vitro and in vivo and could thus be a valuable tool for tracking stem cells noninvasively.

Animals↗
PubMed2002

Catheter-based endomyocardial injection with real-time magnetic resonance imaging.

BACKGROUND: We tested the feasibility of targeted left ventricular (LV) mural injection using real-time MRI (rtMRI). METHODS AND RESULTS: A 1.5T MRI scanner was customized with a fast reconstruction engine, transfemoral guiding catheter-receiver coil (GCC), MRI-compatible needle, and tableside consoles. Commercial real-time imaging software was customized to facilitate catheter navigation and visualization of injections at 4 completely refreshed frames per second. The aorta was traversed and the left ventricular cavity was entered under direct rtMRI guidance. Pigs underwent multiple injections with dilute gadolinium-DTPA. All myocardial segments were readily accessed. The active GCC and the passive Stiletto needle injector were readily visualized. More than 50 endomyocardial injections were performed with the aid of rtMRI; 81% were successful with this first-generation prototype. CONCLUSION: Percutaneous endomyocardial drug delivery is feasible with the aid of rtMRI, which permits precise 3-dimensional localization of injection within the LV wall.

Animals↗
PubMed2002

High temporal resolution phase contrast MRI with multiecho acquisitions.

Velocity imaging with phase contrast (PC) MRI is a noninvasive tool for quantitative blood flow measurement in vivo. A shortcoming of conventional PC imaging is the reduction in temporal resolution as compared to the corresponding magnitude imaging. For the measurement of velocity in a single direction, the temporal resolution is halved because one must acquire two differentially flow-encoded images for every PC image frame to subtract out non-velocity-related image phase information. In this study, a high temporal resolution PC technique which retains both the spatial resolution and breath-hold length of conventional magnitude imaging is presented. Improvement by a factor of 2 in the temporal resolution was achieved by acquiring the differentially flow-encoded images in separate breath-holds rather than interleaved within a single breath-hold. Additionally, a multiecho readout was incorporated into the PC experiment to acquire more views per unit time than is possible with the single gradient-echo technique. A total improvement in temporal resolution by approximately 5 times over conventional PC imaging was achieved. A complete set of images containing velocity data in all three directions was acquired in four breath-holds, with a temporal resolution of 11.2 ms and an in-plane spatial resolution of 2 mm x 2 mm.

Adult↗
PubMed2002

Excitation ratiometric fluorescent biosensor for zinc ion at picomolar levels.

Zinc is a metal ion of increasing significance in several biomedical fields, including neuroscience, immunology, reproductive biology, and cancer. Fluorescent indicators have added greatly to our understanding of the biology of several metal ions, most notably calcium. Despite substantial efforts, only recently have zinc indicators been developed which are sufficiently selective for use in the complex intra- and extracellular milieus, and which are capable of quantifying the free zinc levels with some degree of reliability. However, these indicators (such as FuraZin-1 and Newport Green DCF) have only modest sensitivity, and there is growing evidence that significantly lower levels of free zinc may be biologically relevant in some instances. We have adapted the peerless selectivity and sensitivity of a carbonic anhydrase-based indicator system to an excitation ratiometric format based on resonance energy transfer: i.e., where the zinc ion level is transduced as the ratio of fluorescence intensities excited at two different excitation wavelengths, which is preferred for fluorescence microscopy. The system exhibits more than a 60% increase in the ratio of intensity excited at 365 nm to that excited at 546 nm (emission observed at 617 nm). The detection limit is about 10 pM in zinc buffered systems, a 10-1000-fold improvement on the Fura indicators (which respond to Ca and Mg as well), and a 10 000-fold improvement on the recently described FuraZin-1.

Apoenzymes↗
PubMed2002

Depletion of intracellular zinc from neurons by use of an extracellular chelator in vivo and in vitro.

The membrane-impermeable chelator CaEDTA was introduced extracellularly among neurons in vivo and in vitro for the purpose of chelating extracellular Zn(2+). Unexpectedly, this treatment caused histochemically reactive Zn(2+) in intracellular compartments to drop rapidly. The same general result was seen with intravesicular Zn(2+), which fell after CaEDTA infusion into the lateral ventricle of the brain, with perikaryal Zn(2+) in Purkinje neurons (in vivo) and with cortical neurons (in vitro). These findings suggest either that the volume of zinc ion efflux and reuptake is higher than previously suspected or that EDTA can enter cells and vesicles. Caution is therefore warranted in attempting to manipulate extracellular or intracellular Zn(2+) selectively.

Animals↗