[Prone position ultrasound biomicroscopy for two plateau iris configuration cases with decreased corneal endothelial cells after laser iridotomy]

BACKGROUND

To report a possibility of mechanical injury following laser iridotomy (LI) via the iris surface to the corneal endothelium possibly causing bullous keratopathy.

CASE

Subjects were two patients with plateau iris configuration who had been given LI bilaterally. One eye of each patient showed serious decrease in cellular density of the corneal endothelium. Cataract surgery was carried out in these two eyes. We performed ultrasound biomicroscopy in supine and prone positions for eight directions and specular microscopy for nine directions. Data were compared before and after the surgery. Significant endothelial loss was observed in the lower part of cornea in the two eyes. In the same area, the angular part of the plateau iris was attached to the cornea above the Schwalbe line was also shown in prone position. After the cataract surgery, the attachment was relieved, and the cellular density value of endothelium was increased in the lower area while the value was decreased in other areas. Thereafter, the endothelial decrease stopped.

CONCLUSION

The contact between the iris root and the corneal endothelium might be one cause of bullous keratopathy in eyes with plateau iris following LI.

Dual-modal magnetic resonance and fluorescence imaging of atherosclerotic plaques in vivo using VCAM-1 targeted tobacco mosaic virus

The underlying cause of major cardiovascular events, such as myocardial infarctions and strokes, is atherosclerosis. For accurate diagnosis of this inflammatory disease, molecular imaging is required. Toward this goal, we sought to develop a nanoparticle-based, high aspect ratio, molecularly targeted magnetic resonance (MR) imaging contrast agent. Specifically, we engineered the plant viral nanoparticle platform tobacco mosaic virus (TMV) to target vascular cell adhesion molecule (VCAM)-1, which is highly expressed on activated endothelial cells at atherosclerotic plaques. To achieve dual optical and MR imaging in an atherosclerotic ApoE(-/-) mouse model, TMV was modified to carry near-infrared dyes and chelated Gd ions. Our results indicate molecular targeting of atherosclerotic plaques. On the basis of the multivalency and multifunctionality, the targeted TMV-based MR probe increased the detection limit significantly; the injected dose of Gd ions could be further reduced 400x compared to the suggested clinical use, demonstrating the utility of targeted nanoparticle cargo delivery.

Ultrasound detection of myocardial ischemic memory using an E-selectin targeting peptide amenable to human application

Vascular endothelial leukocyte adhesion molecules, such as E-selectin, are acutely upregulated in myocardial ischemia/reperfusion and are thus "ischemic memory" biomarkers for recent cardiac ischemia. We sought to develop an ultrasound molecular imaging agent composed of microbubbles (MBs) targeted to E-selectin to enable the differential diagnosis of myocardial ischemia in patients presenting with chest pain of unclear etiology. Biodegradable polymer MBs were prepared bearing a peptide with specific human E-selectin affinity (MBESEL). Control MBs had scrambled peptide (MBCTL) or nonspecific IgG (MBIgG). MBESEL adhesion to activated rat endothelial cells (ECs) was confirmed in vitro in a flow system and in vivo with intravital microscopy of rat cremaster microcirculation. Ultrasound molecular imaging of recent myocardial ischemia was performed in rats 4 hours after transient (15 minutes) coronary occlusion. MBESEL adhesion was higher to inflamed versus normal ECs in vitro; there was no difference in MBCTL or MBIgG adhesion to inflamed versus normal ECs. There was greater adhesion of MBESEL to inflamed versus noninflamed microcirculation and minimal adhesion of MBCTL or MBIgG under any condition. Ultrasound imaging after injection of MBSEL demonstrated persistent contrast enhancement of the previously ischemic region. Videointensity in postischemic myocardium after MBESEL was higher than that in the nonischemic bed (11.6 ± 2.7 dB vs 3.6 ± 0.8 dB, p < .02) and higher than that after MBCTL (4.0 ± 1.0 dB, p < .03) or MBIgG (1.7 ± 0.1 dB, p < .03). MBs targeted to E-selectin via a short synthetic peptide with human E-selectin binding affinity enables echocardiographic detection of recent ischemia, setting the stage for clinical myocardial ischemic memory imaging to identify acute coronary syndromes.

Technetium-99m- Arg-Arg-Leu(g2), a modified peptide probe targeted to neovascularization in molecular tumor imaging

PURPOSE

The (131)I-tRRL small peptide probe has been identified in our previous study as a robust tumor molecular radiopharmaceutical that specifically binds to tumor-derived endothelial cells. In this study we developed a smaller structure cyclic tRRL (g2) radiolabeled with (99m)Tc as a novel and optimized peptide probe on tumor angiogenesis molecular imaging.

METHODS

Both tRRL (g2) and control peptide GGG (g2), as well as FITC-RRL (g2) and FITC-GGG (g2) peptide chains were synthesized and characterized by high performance liquid chromatography (HPLC) and electrospray ionization mass spectrometry (EMI-MS) analysis. After synthesis and purification, the peptides were radiolabeled with (99m)Tc by a one-step method for quantitative cell-binding assay and biodistribution experiments. A cell adhesion assay was performed to image tumor-derived endothelial cells-binding specificity with the novel RRL (g2) peptide probe in vitro. The biodistribution experiment was performed to show the tumor uptake of (99m)Tc-RRL (g2) compared with other tissues in human glioblastoma-bearing nude mice in vivo.

RESULTS

FITC-RRL (g2) had significantly higher tumor-derived endothelial cell-binding affinity and specificity than the control FITC-GGG (g2). (99m)Tc-RRL (g2) had higher tumor uptake (2,578 ± 0.293 at 30 min postinjection) and longer tumor retention than (99m)Tc-GGG (g2) in the tumor models tested. The tumor specificity of (99m)Tc-RRL (g2) was also confirmed by successful quantitative cell binding experiments.

CONCLUSION

(99m)Tc-RRL (g2) has more good characteristics such as higher tumor uptake ratio and short half life time compared with (131I)-tRRL. The information obtained here may guide the future development of RRL peptide-based tumor angiogenesis molecular imaging and internal radiotherapeutic agents targeting tumor neovascularity.

Toward ultrasound molecular imaging with phase-change contrast agents: an in vitro proof of principle

Phase-change contrast agents (PCCAs), which normally consist of nanoscale or microscale droplets of liquid perfluorocarbons in an encapsulating shell, can be triggered to undergo a phase transition to the highly echogenic gaseous state upon the input of sufficient acoustic energy. As a result of the subsequent volumetric expansion, a number of unique applications have emerged that are not possible with traditional ultrasound microbubble contrast agents. Although many studies have explored the therapeutic aspects of the PCCA platform, few have examined the potential of PCCAs for molecular imaging purposes. In this study, we demonstrate a PCCA-based platform for molecular imaging using α(v)β(3)-targeted nanoscale PCCAs composed of low-boiling-point perfluorocarbons. In vitro, nanoscale PCCAs adhered to target cells, could be activated and imaged with a clinical ultrasound system and produced a six-fold increase in image contrast compared with non-targeted control PCCAs and a greater than fifty-fold increase over baseline. Data suggest that low-boiling-point nanoscale PCCAs could enable future ultrasound-based molecular imaging techniques in both the vascular and extravascular spaces.

The guanine-nucleotide exchange factor SGEF plays a crucial role in the formation of atherosclerosis

The passage of leukocytes across the endothelium and into arterial walls is a critical step in the development of atherosclerosis. Previously, we showed in vitro that the RhoG guanine nucleotide exchange factor SGEF (Arhgef26) contributes to the formation of ICAM-1-induced endothelial docking structures that facilitate leukocyte transendothelial migration. To further explore the in vivo role of this protein during inflammation, we generated SGEF-deficient mice. When crossed with ApoE null mice and fed a Western diet, mice lacking SGEF showed a significant decrease in the formation of atherosclerosis in multiple aortic areas. A fluorescent biosensor revealed local activation of RhoG around bead-clustered ICAM-1 in mouse aortic endothelial cells. Notably, this activation was decreased in cells from SGEF-deficient aortas compared to wild type. In addition, scanning electron microscopy of intimal surfaces of SGEF^−/− mouse aortas revealed reduced docking structures around beads that were coated with ICAM-1 antibody. Similarly, under conditions of flow, these beads adhered less stably to the luminal surface of carotid arteries from SGEF^−/− mice. Taken together, these results show for the first time that a Rho-GEF, namely SGEF, contributes to the formation of atherosclerosis by promoting endothelial docking structures and thereby retention of leukocytes at athero-prone sites of inflammation experiencing high shear flow. SGEF may therefore provide a novel therapeutic target for inhibiting the development of atherosclerosis.

Low-dose irradiation causes rapid alterations to the proteome of the human endothelial cell line EA.hy926

High doses of ionising radiation damage the heart by an as yet unknown mechanism. A concern for radiological protection is the recent epidemiological data indicating that doses as low as 100-500 mGy may induce cardiac damage. The aim of this study was to identify potential molecular targets and/or mechanisms involved in the pathogenesis of low-dose radiation-induced cardiovascular disease. The vascular endothelium plays a pivotal role in the regulation of cardiac function and is therefore a potential target tissue. We report here that low-dose radiation induced rapid and time-dependent changes in the cytoplasmic proteome of the human endothelial cell line EA.hy926. The proteomes were investigated at 4 and 24 h after irradiation at two different dose rates (Co-60 gamma ray total dose 200 mGy; 20 mGy/min and 190 mGy/min) using 2D-DIGE technology. Differentially expressed proteins were identified, after in-gel trypsin digestion, by MALDI-TOF/TOF tandem mass spectrometry, and peptide mass fingerprint analyses. We identified 15 significantly differentially expressed proteins, of which 10 were up-regulated and 5 down-regulated, with more than ±1.5-fold difference compared with unexposed cells. Pathways influenced by the low-dose exposures included the Ran and RhoA pathways, fatty acid metabolism and stress response.

Ultrasound and microbubble-induced intra- and intercellular bioeffects in primary endothelial cells

Recent developments in the field of ultrasound (US) contrast agents have demonstrated that these encapsulated microbubbles can not only be used for diagnostic imaging but may also be employed as therapeutic carriers for localized, targeted drug or gene delivery. The exact mechanisms behind increased uptake of therapeutic compounds by US-exposed microbubbles are still not fully understood. Therefore, we studied the effects of stably oscillating SonoVue microbubbles on relevant parameters of cellular and intercellular permeability, i.e., reactive oxygen species (ROS) homeostasis, calcium permeability, F-actin cytoskeleton, monolayer integrity and cell viability using live-cell fluorescence microscopy. US was applied at 1-MHz, 0.1MPa peak-negative pressure, 0.2% duty cycle and 20Hz pulse repetition frequency to primary endothelial cells. We demonstrated increased membrane permeability for calcium ions, with an important role for H(2)O(2). Catalase, an extracellular H(2)O(2) scavenger, significantly blocked the influx of calcium ions. Further changes in ROS homeostasis involved an increase in intracellular H(2)O(2) levels, protein nitrosylation and a decrease in total endogenous glutathione levels. In addition, an increase in the number of F-actin stress fibers and F-actin cytoskeletal rearrangement were observed. Furthermore, US-exposed microbubbles significantly affected endothelial monolayer integrity, but importantly, disrupted cell-cell interactions were restored within 30min. Finally, cell viability was not affected. In conclusion, these data provide more insight in the interactions between US, microbubbles and endothelial cells, which is important for understanding the mechanisms behind US and microbubble-enhanced uptake of drugs or genes.

[Comparison between canine decellularized venous valve stent combined with endothelial progenitor cells and native venous valve on venous valve closure mechanism in normal physiological conditions]

OBJECTIVE

To compare canine decellularized venous valve stent combining endothelial progenitor cells (EPC) with native venous valve in terms of venous valve closure mechanism in normal physiological conditions.

METHODS

Thirty-six male hybrid dogs weighing 15-18 kg were used. The left femoral vein with valve from 12 dogs was harvested to prepare decellularized valved venous stent combined with EPC. The rest 24 dogs were randomly divided into the experimental group and the control group (n=12 per group). In the experimental group, EPC obtained from the bone marrow through in vitro amplification were cultured, the cells at passage 3 (5 x 10(6) cells/mL) were seeded on the stent, and the general and HE staining observations were performed before and after the seeding of the cells. In the experimental group, allogenic decellularized valved venous stent combined with EPC was transplanted to the left femoral vein region, while in the control group, the autogenous vein venous valve was implanted in situ. Color Doppler Ultrasound exam was performed 4 weeks after transplantation to compare the direction and velocity of blood flow in the distal and proximal end of the valve, and the changes of vein diameter in the valve sinus before and after the closure of venous valve when the dogs changed from supine position to reverse trendelenburg position.

RESULTS

General and HE staining observations before and after cell seeding: the decellularized valved venous stent maintained its fiber and collagen structure, and the EPC were planted on the decellularized stent successfully through bioreactor. During the period from the reverse trendelenburg position to the starting point for the closure of the valve, the reverse flow of blood occurred in the experimental group with the velocity of (1.4 +/- 0.3) cm/s; while in the control group, there was no reverse flow of blood, but the peak flow rate was decreased from (21.3 +/- 2.1) cm/s to (18.2 +/- 3.3) cm/s. In the control group, the active period of valve, the starting point for the closure of the valve, and the time between the beginning of closure and the complete closure was (918 +/- 46), (712 +/- 48), and (154 +/- 29) ms, respectively; while in the experimental group, it was (989 +/- 53), (785 +/- 43), and (223 +/- 29) ms, respectively. There was significant difference between two groups (P < 0.05). After the complete closure of valve, no reverse flow of blood occurred in two groups. The vein diameter in the valve sinus of the experimental and the control group after the valve closure was increased by 116.8% +/- 2.0% and 118.5% +/- 2.2%, respectively, when compared with the value before valve closure (P > 0.05).

CONCLUSION

Canine decellularized venous valve stent combined with EPC is remarkably different from natural venous valve in terms of the valve closure mechanism in physiological condition. The former relies on the reverse flow of blood and the latter is related to the decreased velocity of blood flow and the increased pressure of vein in the venous sinus segment.

Enhanced caveolae-mediated endocytosis by diagnostic ultrasound in vitro

The modulation of cellular endothelial permeability is a desirable goal for targeted delivery of labels and therapeutic macromolecules; the underlying mechanisms, however, remains poorly understood. Here, we hypothesize that a higher endothelial permeability may result as an outcome of selective enhancement of caveolar endocytosis by ultrasound (US), in the frequency and intensity range of current clinical diagnostic use. To assess the role of free radicals in this phenomenon, we exposed confluent human endothelial cells to pulsed diagnostic US for 30 min, with a mechanical index (MI) of 0.5 and 1.2, using a 1.6-MHz cardiac US scan, and endothelial cells not exposed to US were used as control. Here we show that pulsed diagnostic US with a MI of 1.2 (high mechanical index ultrasound [HMIUS]) were able to selectively enhance endothelial caveolar internalization of recombinant glutathione-S-transferase (GST)-Tat11-EGFP fusion protein (26 +/- 1 vs. 11.6 +/- 1 A.U, p < 0.001 vs. control), without disruption of plasma membrane integrity. Moreover, pulsed diagnostic US with a MI of 0.5 (low mechanical index ultrasound) did not increase caveolar endocytosis compared with control (11.4 +/- 1.2 vs. 11.6 +/- 1). Free-radical generation inhibitors, such as catalase and superoxide dismutase, reduced the HMIUS-induced caveolar internalization by a 49.29% factor; finally, HMIUS-induced caveolar endocytosis was found to be associated with a significant increase in the phosphorylation of tyr-14-caveolin1, ser1177-eNOS and Thr202/Tyr204-ERK(1/2) compared with control. These findings show how HMIUS irradiation of human endothelial cells cause a selective enhancement of caveolar-dependent permeability, partially mediated by free radicals generation, inducing a marked increase of phosphorylation of caveolar-related proteins. Thus, the use of diagnostic US could potentially be used as an adjuvant to drive caveolar traffic of extracellular peptides by using a higher level of US energy.

Anatomical and clinical study on effects of sonography with pulse inversion and microbubble contrast in rabbit kidney

Aim of the present study was to evaluate by transmission electron microscope (TEM) modifications in rabbit kidney-parenchyma after submission to ultrasound contrast agent (UCA) with Pulse Inversion Harmonic Imaging (PIHI). Seven inbred male albino rabbits were divided into three groups: 1) control group (n = 1 animal); 2) sonicated group (n = 3 animals); 3) sonicated group with UCA injection (CEUS) (n = 3 animals). The first group was not exposed to ultrasonography (US) and/or UCA. The second and third groups underwent baseline US and later to US with PIHI with a high mechanical index; in the third group UCA was simultaneously administered. Ultrastructural studies and image analysis were blindly performed on 50 samples (2mm3), including cortex and medulla, by two experienced pathologists with TEM. By TEM observations of the first and second groups showed no structural modifications of renal cortex and medulla. TEM observations of the third group showed ultrastructural changes of renal corpuscle, proximal and distal convoluted tubules and collecting tubules; further in the most of observed sections the filtration membrane had an alteration of typical trilaminar pattern and vacuolisation of glomerular endothelial cells with irregular edges. Therefore in rabbit kidney submitted to CEUS some ultrastructural modifications were observed.

Taspine isolated from Radix et Rhizoma Leonticis inhibits proliferation and migration of endothelial cells as well as chicken chorioallantoic membrane neovascularisation

The aim of the present study was to investigate an anti-angiogenic effect of taspine isolated from Radix et Rhizoma Leonticsi. Taspine was screened for the first time, using cell membrane chromatography (CMC). The anti-angiogeneic activity of taspine was tested by using the chicken chorioallantoic membrane (CAM) neovascularisation model in vivo and the HUVEC proliferation and migration models in vitro, respectively. The results showed that taspine could inhibit CAM angiogenesis significantly within the concentration range of 0.5-2 mug/egg, proliferation and migration of endothelial cells in a dose-dependent manner. The CAM histomorphology results indicated that taspine could inhibit blood vessels sprouts and proliferation of vascular endothelial cell. These findings suggest that taspine is a promising candidate for use as an angiogenesis inhibitor.

Uptake behavior of embryonic chick liver cells

The capacity of selective uptake by liver cells, focusing particularly on the parenchymal and perisinusoidal stellate cells during chick liver development (8-18 days of incubation), was ultrastructurally examined after injection of 240-nm-diameter lecithin (phosphatidylcholine) -coated or noncoated beads into the extraembryonic circulation. Cytoplasmic projections of both cells as well as extrasinusoidal macrophages reached into the sinusoid-like vascular spaces. The primitive perisinusoidal stellate cells were identified by immunocytochemistry as being rich in desmin-positive cytoplasmic intermediate filaments. The cells demonstrated selective uptake of noncoated beads by means of their cytoplasmic projections. These findings were significant in the early period of incubation, indicating that the phagocytic activity is a characteristic and transient phenomenon of developmental differentiation. Large numbers of coated and a few noncoated beads penetrated into the perivascular spaces. The parenchymal cells incorporated only the coated beads that passed through the endothelial lining, suggesting that these cells express selective but limited phagocytic capacity against large "foreign" substances even long before their maturation. The cell projections were not engaged in uptake function. Extrasinusoidal macrophages, Kupffer cells, and intraluminal primitive macrophages all took up both beads; however, lecithin coating of the beads clearly suppressed their uptake function. These data suggest that the uptake function of large "foreign" substances appears to be intrinsic to liver cells and lecithin coating would be useful for delivering large substances to parenchymal cells.

Targeted in vivo imaging of angiogenesis: present status and perspectives

Angiogenesis, the process whereby new capillaries are formed by outgrowth from existing microvessels, is required for tumor growth and metastasis, and is also necessary for natural healing after ischemic injury. Because angiogenesis, excessive or deficient, underlies many pathological situations, there is a need for the development of noninvasive imaging to allow monitoring of angiogenesis related molecular events. Furthermore, specific imaging of angiogenesis would help define the pathophysiology of angiogenesis in living subjects, identify those patients likely to respond to anti-angiogenic or angiogenic therapies, and enable the efficacies of these molecular therapies to be assessed. Herein, we review the targeted imaging of angiogenesis using nuclear medicine modalities (positron emission tomography; PET and single photon emission computed tomography; SPECT) and suitable radiotracers based on potential targets including integrin, extracellular matrix, VEGF and its receptors, activated endothelial cells, and matrix metalloproteinases.

Effect of Microbubble Ligation to Cells on Ultrasound Signal Enhancement

OBJECTIVES

Molecular imaging with contrast-enhanced ultrasound (CEU) relies on the detection of microbubbles retained in regions of disease. The aim of this study was to determine whether microbubble attachment to cells influences their acoustic signal generation and stability.

MATERIALS AND METHODS

Biotinylated microbubbles were attached to streptavidin-coated plates to derive density versus intensity relations during low- and high-power imaging. To assess damping from microbubble attachment to solid or cell surfaces, in vitro imaging was performed for microbubbles charge-coupled to methacrylate spheres and for vascular cell adhesion molecule-1-targeted microbubbles attached to endothelial cells.

RESULTS

Signal enhancement on plates increased according to acoustic power and microbubble site density up to 300 mm. Microbubble signal was reduced by attachment to solid spheres during high- and low-power imaging but was minimally reduced by attachment to endothelial cells and only at low power.

CONCLUSION

Attachment of targeted microbubbles to rigid surfaces results in damping and a reduction of their acoustic signal, which is not seen when microbubbles are attached to cells. A reliable concentration versus intensity relationship can be expected from microbubble attachment to 2-dimensional surfaces until a very high site density is reached.

Absence of Tight Junctions between Microvascular Endothelial Cells in Human Cerebellar Hemangioblastomas

OBJECTIVE:

Endothelial tight junctions form the main barrier of the blood-brain barrier (BBB). In human hemangioblastomas, cyst formation is a common and important clinical manifestation. Although most researchers consider that the cyst formation in hemangioblastomas may be caused by the breakdown of the BBB, the underlying molecular mechanisms for cyst formation remain unknown. At present, there are few reports about the change of tight junctions in microvessel endothelium of human hemangioblastomas. The purpose of this research is to investigate the change of tight junction and its major molecular components in microvessel endothelium of human hemangioblastomas.

METHODS:

Twenty-four consecutive patients with cerebellar hemangioblastomas were studied. Tight junctions in the microvessels of hemangioblastomas and the control brain were examined by electron microscopy. Immunohistochemistry and double immunofluorescent microscopy were used to analyze the expression of CLN5 and its relationship with astrocytic endfeet in the control brain and hemangioblastomas. Quantitative real-time reverse-transcriptase polymerase chain reaction and Western blots were used to investigate the expression level of CLN5 in hemangioblastomas. Triple immunofluorescent microscopy was used to analyze the coexpression of vascular endothelial growth factor, vascular endothelial growth factor-R1, and placenta growth factor on microvessels of hemangioblastomas. Clinical and experimental data were correlated and analyzed by the one-way analysis of variance, Kruskal-Wallis test, and Spearman rank correlation test.

RESULTS:

In the control brain, the paracellular cleft between adjacent endothelial cells is sealed by continuous strands of tight junctions. In cystic hemangioblastomas, a significant paracellular cleft could be found between adjacent endothelial cells. Some endothelial cells were connected with adherens junction and no tight junction was found between them. Compared with the control brain, expression of CLN5 was decreased in cystic hemangioblastomas (P &lt; 0.05). Phosphorylated CLN5 was detected in most hemangioblastomas, but not in the control brain. Microvessels in hemangioblastomas showed a significant absence of astrocytic endfeet. Coexpression of vascular endothelial growth factor, vascular endothelial growth factor-R1, and placenta growth factor was detected in the endothelial cells. The Spearman rank correlation test showed a significant correlation between a greater degree of CLN5 expression and less morphological cystic formation in these patients studied (correlation coefficient = −0.520; P = 0.009).

CONCLUSION:

The continuity of tight junctions of the BBB is interrupted in human cerebellar hemangioblastomas. Significant absence of astrocytic endfeet and tight junctions can be found in microvessels of hemangioblastomas, which may lead to the breakdown of the BBB in these tumors. These findings suggest that the absence of tight junctions might play a role in cyst formation of hemangioblastomas.

Acoustic activation of targeted liquid perfluorocarbon nanoparticles does not compromise endothelial integrity

Perfluorocarbon nanoparticles consisting essentially of liquid perfluoro-octyl bromide (PFOB) core surrounded by a lipid monolayer can serve as highly specific site-targeted contrast and therapeutic agents after binding to cellular biomarkers. Based on previous findings that ultrasound applied at 2 MHz and 1.9 mechanical index (MI) for a 5-min duration dramatically enhances the cellular interaction of targeted PFOB nanoparticles with melanoma cells in vitro without inducing apoptosis or other harmful effects to cells that are targeted, we sought to define mechanisms of interaction and the safety profile of ultrasound used in conjunction with liquid perfluorocarbon nanoparticles for targeted drug delivery, as compared with conventional microbubble ultrasound contrast agents under identical insonification conditions. Cell-culture inserts were used to grow a confluent monolayer of human umbilical vein endothelial cells. Definity in conjunction with continuous wave ultrasound (2.25 MHz for 1 and 5 min) increased the permeability of monolayer by four to six times above the normal, decreased transendothelial electrical resistance (a sign of reduced membrane integrity), and decreased cell viability by approximately 50%. Histological evaluation demonstrated extensive disruptions of cell monolayers. Nanoparticles (both nontargeted and targeted) elicited no changes in these different measures under similar insonification conditions and did not disrupt cell monolayers. We hypothesize that ultrasound facilitates drug transport from the perfluorocarbon nanoparticles not by cavitation-induced effects on cell membrane but rather by direct interaction with the nanoparticles that stimulate lipid exchange and drug delivery.

Effects of shear stress on endothelial cells: possible relevance for ultrasound applications

This review forms part of a series of papers resulting from a workshop on safety of ultrasound applications. The physical effects of ultrasound include generation of steady streaming in large fluid volumes, and micro-streaming around contrast bubbles. Such streaming induces shear stress acting on the vascular endothelium. This review provides a discussion on the levels of endothelial shear stress associated with diagnostic ultrasound applications, and on the biological effects of shear stress acting on the endothelial cells. Depending on vessel size and ultrasound characteristics, shear stresses associated with streaming and micro-streaming may exceed the physiological levels associated with the flow of blood by many orders of magnitude. The resulting biological effects could range anywhere from activation of normal shear stress sensors such as ion channels, damage of the endothelial surface layer, reversible perforation of the membrane, to cell detachment and lysis. The possible presence of such biological effects does not necessarily mean that the effects are harmful for the individual. However, considering the ever-increasing use of ultrasound, a further investigation into these shear stress-related effects, using both experiments and modelling, is desired. Apart from safety concerns, such effects may provide a base for strategies aimed at targeted delivery of drugs.

Labelling of human mesenchymal stem cells with indium-111 for SPECT imaging: effect on cell proliferation and differentiation

PURPOSE

Stem cell therapy seems to be a new treatment option within cardiac diseases to improve myocardial perfusion and function. However, the delivery and traceability of the cells represent a problem. Radioactive labelling with 111In could be a method for tracking mesenchymal stem cells (MSCs). However, 111In could influence the viability and differentiation capacity of MSCs, which would limit its use. Therefore, the aim of this study was to evaluate the influence of 111In labelling in doses relevant for SPECT imaging in humans on the viability and differentiation capacity of human MSCs.

METHODS AND RESULTS

Human MSCs isolated from bone marrow were incubated with 111In-tropolone (15-800 Bq/cell). The labelling efficiency was approximately 25% with 30 Bq/cell 111In. The MSC doubling time was 1.04+/-0.1 days and was not influenced by 111In within the range 15-260 Bq/cell. Using 30 Bq 111In/cell it was possible to label MSCs to a level relevant for clinical scintigraphic use. With this dose, 111In had no effect on characteristic surface and intracellular markers of cultured MSCs analysed both by flow cytometry and by real-time polymerase chain reaction. Further, the labelled MSCs differentiated towards endothelial cells and formed vascular structures.

CONCLUSION

It is possible to label human MSCs with 111In for scintigraphic tracking of stem cells delivered to the heart in clinical trials without affecting the viability and differentiation capacity of the MSCs. This creates an important tool for the control of stem cell delivery and dose response in clinical cardiovascular trials.

Characteristics and regulation of 123I-MIBG transport in cultured pulmonary endothelial cells

123I-Metaiodobenzylguanidine (123I-MIBG) is used for lung scintigraphy to assess pulmonary endothelial cell integrity, but its processing at the cellular level has not been investigated to date. We thus characterized the mechanisms that mediate 123I-MIBG transport in pulmonary endothelial cells and investigated the effects of stimuli associated with pulmonary dysfunction.

METHODS

Calf pulmonary artery endothelial (CPAE) cells were examined for 123I-MIBG uptake and efflux rates and evaluated for the presence of norepinephrine (NE) transporters by Western blotting. The specificity of 123I-MIBG uptake was investigated with inhibitors of the uptake 1 and uptake 2 transport systems. In addition, we tested the effects of hypoxia (1% O2), phorbol 12-myristate 13-acetate (PMA, a protein kinase C [PKC] activator), and NG-nitro-L-arginine methyl ester (L-NAME) (a nitric oxide synthase inhibitor) treatments on CPAE cell 123I-MIBG uptake.

RESULTS

CPAE cells demonstrated a time-dependent increase in 123I-MIBG uptake that reached a relative plateau (mean +/- SD) at 4 h of 375.6% +/- 5.9% the 30-min level. When the culture medium was changed after 30 min of uptake, 123I-MIBG gradually was eluted from the cells at an efflux rate of 43.8% over 2 h. Western blotting confirmed the presence of NE transporters in CPAE cells. The uptake 1 inhibitors desipramine, imipramine, and phenoxybenzamine at 50 micromol/L reduced 123I-MIBG uptake to 55.3% +/- 2.7%, 62.4% +/- 3.5%, and 48.0% +/- 2.2% control levels, respectively, whereas none of the uptake 2 inhibitors had an effect. Exposure to hypoxia resulted in a reduction in 123I-MIBG uptake to 77.5% +/- 0.2% and 50.0% +/- 3.4% control levels at 0.5 and 4 h, respectively. PMA (10 ng/mL) and L-NAME (2 nmol/L) decreased 123I-MIBG uptake to 76.7% +/- 9.0% and 86.5% +/- 5.6% control levels, respectively.

CONCLUSION

Pulmonary endothelial cells express NE transporters and actively take up 123I-MIBG through the specific uptake 1 system. Furthermore, 123I-MIBG transport can be reduced by hypoxia, PKC activation, and nitric oxide deficiency, which may contribute partly to the lower levels of lung uptake observed in diseases that compromise pulmonary endothelial cell integrity.

Synthesis and evaluation of 4-[18F]fluorothalidomide for the in vivo studies of angiogenesis

In this study, we prepared 2-(2,6-dioxopiperidin-3-yl)-4-[(18)F]fluoroisoindole-1,3-dione (4-[(18)F]fluorothalidomide; [(18)F]1) for the in vivo studies of angiogenesis. Radiochemical synthesis of [(18)F]1 was carried out by labeling 4-trimethylammoniumthalidomide trifluoromethanesulfonate with nBu(4)N[(18)F]F in dimethyl sulfoxide (DMSO), followed by reverse-phase HPLC purification. Decay-corrected radiochemical yield of [(18)F]1 was 50-60%, with an effective specific activity of 42-120 GBq/micromol (end of synthesis). Incubation of the radioligand with human umbilical vein endothelial cells (HUVEC-C; American Type Culture Collection) showed a time-dependent increase in the uptake of the radioligand, and the uptake was inhibited by 8-11% in the presence of 10 microM thalidomide, indicating nonspecific binding of the radioligand. Positron emission tomography (PET) images of mice implanted with tumors in their right flanks revealed a marked accumulation of radioactivity in the livers, kidneys and bladders of the mice, and brain uptake appeared at approximately 40 min after injection. However, no radioactivity uptake was detected in the implanted tumor. Thin-layer chromatography (TLC), HPLC and LC-MS analyses of mouse liver microsomal metabolites of [(18)F]1 and 1 with or without nicotinamide adenine dinucleotide phosphate (NADPH) clearly revealed that the radioligand did not go through metabolic activation but underwent nonenzymatic hydrolysis at physiological pH. Therefore, these results would appear to indicate that [(18)F]1 may not be suitable for the in vivo studies of angiogenesis at least in mice, although it was reported that thalidomide and/or its hydrolysis products may be responsible for its activity in humans.

Wall shear stress and related hemodynamic parameters in the fetal descending aorta derived from color Doppler velocity profiles

This paper presents a methodology for estimating the wall shear stress in the fetal descending aorta from color Doppler velocity profiles obtained during the second half of pregnancy. The Womersley model was applied to determine the wall shear stress and related hemodynamic parameters. Our analysis indicates that the aortic diameter can be modeled as a function of the gestational age in weeks as: Diameter (mm) = 0.17.ga + 0.15 (R2 = 0.64, p < 0.001). The aortic volume flow showed a log linear gestational age-related increase that fit the model: F (mL/min) = e(0.08.ga + 3.49) (R2 = 0.61, p < 0.001). The Womersley number increased linearly with gestational age from 3.3 to 6.2 (p < 0.001) and the pressure gradient decreased linearly from 2.68 to 1.16 mPa/mm (p = 0.003) during the second half of pregnancy; the mean wall shear stress for the study group was 2.2 Pa (SD = 0.59) and was independent of gestational age. This study suggests that the size of the fetal aorta adapts to flow demands and maintains constant mean wall shear stress.

Distribution and pharmacokinetic analysis of angiostatin radioiodine labeled with high stability

OBJECTIVE

Radiotracers of anticancer agents provide important information on its in vivo handling. Angiostatin (AST) is a promising anticancer drug with potent antiangiogenic effects, but reported AST radiotracers suffer from poor in vivo stability. In this study, we synthesized an AST probe radioiodinated via the Bolton-Hunter reagent (125I-BH-AST) and investigated its stability and biokinetics in mice.

METHODS

125I-BH-AST and conventional direct radioiodinated 125I-AST were evaluated for human endothelial cell binding characteristics. In vivo stability of the radiotracers was compared by biodistribution studies in normal ICR mice. Angiostatin pharmacokinetics was analyzed by serial blood sampling after intravenous injection of 125I-BH-AST with varying AST concentrations in mice.

RESULTS

Both 125I-AST and 125I-BH-AST retained selective endothelial binding as demonstrated by dose-dependent inhibition by nonradiolabeled AST. 125I-BH-AST was substantially more stable in mice than 125I-AST, with 28- and 7-fold lower 24-h thyroid and blood activities, respectively (15.5+/-1.5 vs. 430.9+/-32.2 and 0.1+/-0.0 vs. 0.8+/-0.0 %ID/g; both P<.005). Using (125)I-BH-AST, we found that 24-h AST accumulation was highest in the kidneys, followed by the liver and lungs. Kinetic analysis of 125I-BH-AST revealed AST to have linear pharmacokinetics with a T(1/2) of 5.8+/-2.6 h, volume of distribution (V(d)) of 6.8+/-1.3 ml and clearance of 0.8+/-0.1 ml/h.

CONCLUSION

Radioiodine-labeled AST prepared by the BH method provides a radioprobe with superior stability and improved in vivo biokinetics that is useful for distribution and pharmacokinetic studies.

Identification of a new prostate-specific cyclic peptide with the bacterial FliTrx system

Peptides are useful tools for directing radioisotopes into tumors. We evaluated the ability of a bacterial peptide display system to isolate new prostate tumor-specific peptides.

METHODS

We used the bacterial FliTrx system to identify a new cyclic peptide that binds to prostate carcinoma. Serum stability and binding affinities of the (125)I-labeled peptide were tested. Furthermore, the (131)I-labeled peptide was used to evaluate its biodistribution.

RESULTS

Several peptides showing a potential consensus motif were identified. The new peptide MM-2 is stable in serum for up to 24 h. It binds to PC-3 cells, and this binding can be inhibited more than 70% with the unlabeled peptide. Binding to human umbilical vein endothelial cells (HUVECs) and PNT-2 cells is weaker, and competition (27%) in HUVECs is less efficient. The biodistribution showed moderate accumulation in tumor.

CONCLUSION

Bacterial peptide display, an alternative to phage peptide display, can allow the identification of specific binding and stable peptides.

Bioeffect of ultrasound on endothelial cells in vitro

The effects of low-intensity ultrasound (US) on biological systems have been investigated extensively; however, the effects of ultrasound stimulation on endothelial cells were rarely studied. In this study, 1 MHz, pulsed 1:4, and four different spatial-average temporal-peak intensities (0.5, 1.0, 1.6, and 2W/cm2) of ultrasound were used to stimulate endothelial cells for 10 min per day. The results showed that ultrasound (intensity 1.6-2.0W/cm2) treatment after 6 days enhanced the nitric oxide (NO) and Ca2+ release from the endothelial cells but did not promote cell growth. In addition, ultrasound stimulation changed the cellular morphology and orientation, and increased extracellular matrix secretion from endothelial cells.

Nitric oxide stimulates 18F-FDG uptake in human endothelial cells through increased hexokinase activity and GLUT1 expression

The endothelium constitutes a functionally active organ critically involved in angiogenesis. Nitric oxide (NO) is an important regulator of vascular homeostasis and angiogenesis and stimulates glucose metabolism in certain cells. We thus investigated the effect of exogenous NO on (18)F-FDG transport in human endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with the NO donors sodium nitroprusside (SNP) or diethylenetriamine (DETA), in concentrations of 1 micromol/L-1 mmol/L for up to 24 h. (18)F-FDG uptake levels corrected for protein content were determined by cellular radioactivity measured after 30-min incubation. Cells were evaluated for total hexokinase activity and plasma membrane glucose transporter 1 (GLUT1) levels, and involvement of potential signaling pathways was investigated by cotreatment with respective protein kinase inhibitors.

RESULTS

Both SNP and DETA stimulated HUVEC (18)F-FDG uptake, which began at 16 h and peaked at 24 h. The increase in (18)F-FDG uptake was dose dependent, reaching 464.0% +/- 49.8% and 254.5% +/- 10.8% of control levels at 24 h with 1 mmol/L SNP and DETA, respectively. Exposure of HUVECs to 1 mmol/L SNP resulted in a 3.5 +/- 0.3-fold elevation in hexokinase activity (P < 0.01) and a significant increase in GLUT1 levels. SNP-stimulated (18)F-FDG uptake was abolished by cotreatment with cycloheximide, the tyrosine kinase inhibitor genistein, the phosphatidylinositol-3 kinase (PI3K) inhibitor wortmannin, or the protein kinase C inhibitor staurosporine.

CONCLUSION

NO stimulates (18)F-FDG uptake in HUVECs through an increase in GLUT1 expression and hexokinase activity, which appears to involve both protein kinase C and PI3K pathways.

Involvement of pulmonary endothelial cell injury in the pathogenesis of pulmonary fibrosis: clinical assessment by 123I-MIBG lung scintigraphy

PURPOSE

Pulmonary microvascular endothelial injury may be involved in the pathogenesis of pulmonary fibrosis (PF). The aim of this study was to evaluate the pulmonary vascular status in patients with PF by lung scintigraphic assessment of 123I-metaiodobenzylguanidine (123I-MIBG), which reflects latent endothelial cell lesions.

METHODS

We assessed lung 123I-MIBG kinetics and clinical indices in 23 PF patients and 16 controls. Mean uptake ratios of lung to mediastinum (L/M) were calculated in anterior planar images at 30 (early image) and 270 (delayed image) min after intravenous injection of 123I-MIBG. The pulmonary mean washout rate (WR) of 123I-MIBG was also calculated.

RESULTS

The L/M ratio in early images, but not in delayed images, was significantly lower in the PF patients than in the controls (L/M(early) 1.41+/-0.14 vs 1.53+/-0.10, p<0.01; L/M(delayed) 1.28+/-0.10 vs 1.33+/-0.07, p=NS). WR was significantly reduced in the PF patients compared with the controls (28.6%+/-3.1% vs 34.2%+/-5.1%, p<0.001). In the study subjects (PF patients plus controls) there were significant relationships between lung WR of (123)I-MIBG and other diagnostic parameters for the severity of PF, such as vital capacity (r=0.625, p<0.0001), total lung capacity (r=0.691, p<0.0001), carbon monoxide diffusing capacity (r=0.622, p<0.0001), serum angiotensin-converting enzyme activity (r=0.422, p<0.01), carbohydrate antigen KL-6 levels (r=-0.495, p<0.01) and surfactant protein-D levels (r=-0.461, p<0.01). When control subjects were excluded, similar significant correlations were observed between WR and %TLC (r=0.508, p<0.05), DL(CO) (r=0.593, p<0.01) and serum ACE activity (r=0.515, p<0.05) in the PF patients.

CONCLUSION

These results suggest that endothelial cell injury plays a significant role in the pathogenesis of PF, and that lung WR of 123I-MIBG, which is a specific marker of endothelial damage, can serve as a novel diagnostic tool to evaluate the functional severity of PF.

Micromanipulation of endothelial cells: ultrasound-microbubble-cell interaction

Ultrasound (US) in combination with contrast microbubbles has been shown to alter the permeability of cell membranes without affecting cell viability. This permeabilisation feature is used to design new drug delivery systems using US and contrast agents. The underlying mechanisms are still unknown. One hypothesis is that oscillating microbubbles cause cell deformation resulting in enhanced cell membrane permeability. This technical note reveals the interaction between oscillating microbubbles and endothelial cells under a microscope recorded with a fast framing camera at 10 million frames per second. A microbubble expansion of 100% resulted a 2.3-mum displacement of the cell membrane. During the insonification, changes of approximately 15% in the cross-sectional distance of the endothelial cells were observed due to microbubble vibrations. In conclusion, the use of such a camera makes it possible to reveal the mechanisms of interactions between ultrasound, microbubbles and cells.