Kaibin Tan

Myocardium-targeted transplantation of mesenchymal stem cells by diagnostic ultrasound-mediated microbubble destruction improves cardiac function in myocardial infarction of New Zealand rabbits.

BACKGROUND Therapeutic ultrasound-mediated microbubble destruction has been applied in the targeted delivery of genes, drugs and stem cells. We intended to study whether diagnostic US irradiating lipid-coated microbubble destruction combined with bone-marrow derived MSC infusion could enable the targeted delivery of MSCs into the myocardium and improve cardiac function of the myocardial infarction of New Zealand rabbits. METHODS Diagnostic ultrasound was applied to the anterior chest for 10 min after intravenous injection of lipid-coated microbubble followed by infusion of BM-MSCs. Echocardiography, histological examination, and western blotting were performed 4 weeks after cell transplantation. RESULTS The cardiac function (assessed by fractional shortening and ejection fraction) was markedly improved by US+Microbubble+MSC treatment. The number of capillaries stained by HE in US+Microbubble+MSC group (47+/-23) was much greater than that of the MSCs infusion group (26+/-7), US+Microbubble group(22+/-5) and PBS infusion group (19+/-10), P<0.01. US+Microbubble stimulation induced the expression of adhesion molecule (VCAM-1) in capillaries and enhanced the myocardial permeability of microvessels. US+Microbubble-mediated supply of MSCs increased the level of VEGF in ischemic myocardium. Area of cardiac fibrosis in the US+Microbubble+MSC group was significantly decreased by 25.6%,40.1% and 46.8% when compared with MSC infusion group, US+Microbubble group and PBS infusion group, respectively. CONCLUSIONS This non-invasive cell delivery system may be useful as a novel and efficient approach for angiogenic cell therapy to the infarcted myocardium.

Disruption of Tumor Neovasculature by Microbubble Enhanced Ultrasound: A Potential New Physical Therapy of Anti-Angiogenesis

Tumor angiogenesis is of vital importance to the growth and metastasis of solid tumors. The angiogenesis is featured with a defective, leaky and fragile vascular construction. Microbubble enhanced ultrasound (MEUS) cavitation is capable of mechanical disruption of small blood vessels depending on effective acoustic pressure amplitude. We hypothesized that acoustic cavitation combining high-pressure amplitude pulsed ultrasound (US) and circulating microbubble could potentially disrupt tumor vasculature. A high-pressure amplitude, pulsed ultrasound device was developed to induce inertial cavitation of circulating microbubbles. The tumor vasculature of rat Walker 256 was insonated percutaneously with two acoustic pressures, 2.6 MPa and 4.8 MPa, both with intravenous injection of a lipid microbubble. The controls were treated by the ultrasound only or sham ultrasound exposure. Contrast enhanced ultrasound (CEUS) and histology were performed to assess tumor circulation and pathological changes. The CEUS results showed that the circulation of Walker 256 tumors could be completely blocked off for 24 hours in 4.8 MPa treated tumors. The CEUS gray scale value (GSV) indicated that there was significant GSV drop-off in both of the two experimental groups but none in the controls. Histology showed that the tumor microvasculature was disrupted into diffuse hematomas accompanied by thrombosis, intercellular edema and multiple cysts formation. The 24 hours of tumor circulation blockage resulted in massive necrosis of the tumor. MEUS provides a new, simple physical method for anti-angiogenic therapy and may have great potential for clinical applications.

Kidney-Targeted Transplantation of Mesenchymal Stem Cells by Ultrasound-Targeted Microbubble Destruction Promotes Kidney Repair in Diabetic Nephropathy Rats

We test the hypothesis that ultrasound-targeted microbubble destruction (UTMD) technique increases the renoprotective effect of kidney-targeted transplantation of bone-marrow-derived mesenchymal stem cells (BM-MSCs) in diabetic nephropathy (DN) rats. Diabetes was induced by streptozotocin injection (60 mg/Kg, intraperitoneally) in Sprague-Dawley rats. MSCs were administered alone or in combination with UTMD to DN rats at 4 weeks after diabetes onset. Random blood glucose concentrations were measured at 1, 2, 4, and 8 weeks, and plasma insulin levels, urinary albumin excretion rate (UAER) values, the structures of pancreas and kidney, the expressions of TGF-β1, synaptopodin, and IL-10 were assessed at 8 weeks after MSCs transplantation. MSCs transplantation decreased blood glucose concentrations and attenuated pancreatic islets/β cells damage. The permeability of renal interstitial capillaries and VCAM-1 expression increased after UTMD, which enhanced homing and retention of MSCs to kidneys. MSCs transplantation together with UTMD prevented renal damage and decreased UAER values by inhibiting TGF-β1 expression and upregulating synaptopodin and IL-10 expression. We conclude that MSCs transplantation reverts hyperglycemia; UTMD technique noninvasively increases the homing of MSCs to kidneys and promotes renal repair in DN rats. This noninvasive cell delivery method may be feasible and efficient as a novel approach for personal MSCs therapy to diabetic nephropathy.

Ultrasound-targeted stromal cell-derived factor-1-loaded microbubble destruction promotes mesenchymal stem cell homing to kidneys in diabetic nephropathy rats

Mesenchymal stem cell (MSC) therapy has been considered a promising strategy to cure diabetic nephropathy (DN). However, insufficient MSCs can settle in injured kidneys, which constitute one of the major barriers to the effective implementation of MSC therapy. Stromal cell-derived factor-1 (SDF-1) plays a vital role in MSC migration and involves activation, mobilization, homing, and retention, which are presumably related to the poor homing in DN therapy. Ultrasound-targeted microbubble destruction has become one of the most promising strategies for the targeted delivery of drugs and genes. To improve MSC homing to DN kidneys, we present a strategy to increase SDF-1 via ultrasound-targeted microbubble destruction. In this study, we developed SDF-1-loaded microbubbles (MBSDF-1) via covalent conjugation. The characterization and bioactivity of MBSDF-1 were assessed in vitro. Target release in the targeted kidneys was triggered with diagnostic ultrasound in combination with MBSDF-1. The related bioeffects were also elucidated. Early DN was induced in rats with streptozotocin. Green fluorescent protein-labeled MSCs were transplanted intravenously following the target release of SDF-1 in the kidneys of normal and DN rats. The homing efficacy was assessed by detecting the implanted exogenous MSCs at 24 hours. The in vitro results showed an impressive SDF-1 loading efficacy of 79% and a loading content of 15.8 μg/mL. MBSDF-1 remained bioactive as a chemoattractant. In the in vivo study, SDF-1 was successfully released in the targeted kidneys. The homing efficacy of MSCs to DN kidneys after the target release of SDF-1 was remarkably ameliorated at 24 hours compared with control treatments in normal rats and DN rats. In conclusion, ultrasound-targeted MBSDF-1 destruction could promote the homing of MSCs to early DN kidneys and provide a novel potential therapeutic approach for DN kidney repair.

Ultrasound-Targeted Microbubble Destruction Improves the Migration and Homing of Mesenchymal Stem Cells after Myocardial Infarction by Upregulating SDF-1/CXCR4: A Pilot Study

Mesenchymal stem cell (MSC) therapy shows considerable promise for the treatment of myocardial infarction (MI). However, the inefficient migration and homing of MSCs after systemic infusion have limited their therapeutic applications. Ultrasound-targeted microbubble destruction (UTMD) has proven to be promising to improve the homing of MSCs to the ischemic myocardium, but the concrete mechanism remains unclear. We hypothesize that UTMD promotes MSC homing by upregulating SDF-1/CXCR4, and this study was aimed at exploring this potential mechanism. We analyzed SDF-1/CXCR4 expression after UTMD treatment in vitro and in vivo and counted the number of homing MSCs in MI areas. The in vitro results demonstrated that UTMD not only led to elevated secretion of SDF-1 but also resulted in an increased proportion of MSCs that expressed surface CXCR4. The in vivo findings show an increase in the number of homing MSCs and higher expression of SDF-1/CXCR4 in the UTMD combined with MSCs infusion group compared to other groups. In conclusion, UTMD can increase SDF-1 expression in the ischemic myocardium and upregulate the expression of surface CXCR4 on MSCs, which provides a molecular mechanism for the homing of MSCs assisted by UTMD via SDF-1/CXCR4 axis.

Assessment of left ventricular function by three-dimensional speckle-tracking echocardiography in well-treated type 2 diabetes patients with or without hypertension.

The aims of this study were to investigate the myocardial deformation in well‐treated type 2 diabetes patients with or without hypertension using three‐dimensional speckle‐tracking echocardiography and to explore variables that could affect myocardial deformation.

Vascular Effects of Microbubble-Enhanced, Pulsed, Focused Ultrasound on Liver Blood Perfusion

The purpose of this study was to investigate the vascular effects of microbubble-enhanced pulsed high-pressure ultrasound on liver blood perfusion. In the presence of circulating lipid-shell microbubbles, a focused ultrasound transducer was used to transcutaneously treat eight livers of healthy rabbits for perfusion analysis and to treat three livers with the abdomen open for histologic analysis. Twenty-two livers treated with the ultrasound only (n = 11) or microbubbles only (n = 11) served as the controls. The focused ultrasound was operated at a frequency of 1.22 MHz with a peak negative pressure of 4.6 MPa. The liver blood perfusion was estimated by performing contrast-enhanced ultrasound and gray-scale quantification on the livers before and after treatment. A temporary, nonenhanced region occurred in all of the experimental livers. The regional contrast gray-scale values of the experimental group dropped significantly from 88.4 before treatment to 2.7 after treatment. The liver perfusion also demonstrated a gradual recovery over a 60-min period. The liver perfusion of the control groups remained the same after treatment. We found microvascular rupture, hemorrhage and swelling hepatocytes upon histologic examination of the experimental group. Regional liver blood perfusion can be temporarily blocked by microbubble-enhanced focused ultrasound with high-pressure amplitude. These vascular effects can be explained as acute microvascular injury of the liver and may have clinical implications.

Endothelial adhesion of targeted microbubbles in both small and great vessels using ultrasound radiation force.

The effectiveness of microbubble-mediated ultrasound molecular imaging and drug delivery has been significantly affected by the axial laminar flow of vessels which prevents ultrasound contrast agents (UCAs) from targeting vascular endothelium. Studies show that acoustic manipulation could increase targeted UCA adhesion in microcirculation and some small vessels. In this study we demonstrate that ultrasound radiation force (USRF) can also significantly enhance the targeted adhesion of microbubbles in both small and great vessels. Our results indicate that the UCA adhesion targeted to ICAM-1 expressed on mouse cremaster microvascular endothelial cells increase about 9-fold when USRF is applied at 1 MHz and 73.9 kPa. The adhesion of anti-CD34 microbubbles to the endothelia of rat abdominal aorta was visually analyzed using scanning electron microscopy for the first time and thousands of microbubbles were found attached to the aortic endothelia after USRF application at the same acoustic parameters. Our data illustrate that targeted adhesion of anti-CD34 microbubbles is possible in normal abdominal aorta and we demonstrate the potential of using USRF in molecular imaging of a vascular target.

Preparation and characterization of a nanoscale ultrasound contrast agent.

OBJECTIVE The purpose of the present study is to prepare a nanoscale ultrasound contrast agent and to investigate its characterization and ultrasonic imaging in vivo. METHODS Nanoscale ultrasound contrast agent was prepared by machine vibration and low speed centrifugation, and the appearance, distribution, diameter, and zeta potential of the nanoscale ultrasound contrast agent were measured. Contrast-enhanced ultrasonography was performed on normal rabbit liver to observe the duration and intensity of enhancement. RESULTS The nanoscale ultrasound contrast agent had a good shape and uniform distribution by light microscope and transmission electron microscope, with average diameters of 623.4 nm and average zeta potential of 1.3 mV. The contrast imaging study in vivo showed that the nanoscale ultrasound contrast agent could significantly enhance the duration and echo intensity of the vessels and parenchyma in rabbit livers, and there were no obvious difference with micro-scale microbubbles. CONCLUSIONS The nanoscale ultrasound contrast agent is stable and effective for the enhancement of ultrasound imaging. This study provides an important platform for miniaturizing and improving the targeting performance of ultrasound contrast agents.

Renal interstitial permeability changes induced by microbubble-enhanced diagnostic ultrasound.

Abstract Ultrasound-targeted microbubble (MB) destruction (UTMD) has been shown to increase the glomerular permeability, providing a potential novel therapeutic approach in targeted drug release for kidney diseases. Therefore, we investigated the impact of UTMD on renal interstitial permeability using MB-mediated diagnostic ultrasound (DUS). The left kidney of Sprague–Dawley (SD) rat was insonated by UTMD with either continuous or intermittent mode for 5 min. Evans blue (EB) revealed that both modes induced renal vascular permeability increase after DUS but recovered after 24 h. Intermittent insonation caused more severe injury than continuous mode. Red blood cells leaked out of the capillaries into interstitium without glomerular capillary hemorrhage (GCH) by hematoxylin and eosin (HE) staining. Electronic microscopy revealed the disruption of focal capillary wall in interstitial tissues. Morphological results confirmed capillary wall recovered in 24 h post-treatment. Results from fluorescence-labeled MBs showed that MBs were mainly localized in the interstitial portion of the tubular region and retained at 24 h. Intriguingly, urinalysis showed no clinical proteinuria after treatment. Our results indicated that MB plus DUS specifically and reversibly enhanced the interstitial permeability without affecting glomerulus, which may be developed into a therapeutic approach for targeting drug release to individual renal compartments.