Targeted delivery of bone marrow mononuclear cells by ultrasound destruction of microbubbles induces both angiogenesis and arteriogenesis response

Systematic review and meta-analysis of the effect of bone marrow-derived cell therapies on hind limb perfusion

Preclinical and clinical studies on the administration of bone marrow-derived cells to restore perfusion show conflicting results. We conducted a systematic review and meta-analysis on preclinical studies to assess the efficacy of bone marrow-derived cells in the hind limb ischemia model and identify possible determinants of therapeutic efficacy. In vivo animal studies were identified using a systematic search in PubMed and EMBASE on 10 January 2022. 85 studies were included for systematic review and meta-analysis. Study characteristics and outcome data on relative perfusion were extracted. The pooled mean difference was estimated using a random effects model. Risk of bias was assessed for all included studies. We found a significant increase in perfusion in the affected limb after administration of bone marrow-derived cells compared to that in the control groups. However, there was a high heterogeneity between studies, which could not be explained. There was a high degree of incomplete reporting across studies. We therefore conclude that the current quality of preclinical research is insufficient (low certainty level as per GRADE assessment) to identify specific factors that might improve human clinical trials.

State of the field: cellular and exosomal therapeutic approaches in vascular regeneration

Pathologies of the vasculature including the microvasculature are often complex in nature, leading to loss of physiological homeostatic regulation of patency and adequate perfusion to match tissue metabolic demands. Microvascular dysfunction is a key underlying element in the majority of pathologies of failing organs and tissues. Contributing pathological factors to this dysfunction include oxidative stress, mitochondrial dysfunction, endoplasmic reticular (ER) stress, endothelial dysfunction, loss of angiogenic potential and vascular density, and greater senescence and apoptosis. In many clinical settings, current pharmacologic strategies use a single or narrow targeted approach to address symptoms of pathology rather than a comprehensive and multifaceted approach to address their root cause. To address this, efforts have been heavily focused on cellular therapies and cell-free therapies (e.g., exosomes) that can tackle the multifaceted etiology of vascular and microvascular dysfunction. In this review, we discuss 1) the state of the field in terms of common therapeutic cell population isolation techniques, their unique characteristics, and their advantages and disadvantages, 2) common molecular mechanisms of cell therapies to restore vascularization and/or vascular function, 3) arguments for and against allogeneic versus autologous applications of cell therapies, 4) emerging strategies to optimize and enhance cell therapies through priming and preconditioning, and, finally, 5) emerging strategies to bolster therapeutic effect. Relevant and recent clinical and animal studies using cellular therapies to restore vascular function or pathologic tissue health by way of improved vascularization are highlighted throughout these sections.

Advanced clinical imaging for the evaluation of stem cell based therapies

Introduction: As stem cell treatments reach closer to the clinic, the need for appropriate noninvasive imaging for accurate disease diagnosis, treatment planning, follow-up, and early detection of complications, is constantly rising. Clinical radiology affords an extensive arsenal of advanced imaging techniques, to provide anatomical and functional information on the whole spectrum of stem cell treatments from diagnosis to follow-up.Areas covered: This manuscript aims at providing a critical review of major published studies on the utilization of advanced imaging for stem cell treatments. Uses of magnetic resonance imaging (MRI), computed tomography (CT), ultrasound, and positron emission tomography (PET) are reviewed and interrogated for their applicability to stem cell imaging.Expert opinion: A wide spectrum of imaging methods have been utilized for the evaluation of stem cell therapies. The majority of published techniques are not clinically applicable, using methods exclusively applicable to animals or technology irrelevant to current clinical practice. Harmonization of preclinical methods with clinical reality is necessary for the timely translation of stem cell therapies to the clinic. Methods such as diffusion weighted MRI, hybrid imaging, and contrast-enhanced ultrasound hold great promise and should be routinely incorporated in the evaluation of patients receiving stem cell treatments.

Ultrasound‑targeted microbubble destruction‑mediated Galectin‑7‑siRNA promotes the homing of bone marrow mesenchymal stem cells to alleviate acute myocardial infarction in rats

Bone marrow mesenchymal stem cells (BMSCs) are accepted as a form of cellular therapy to improve cardiac function following acute myocardial infarction (AMI). The present study was performed to investigate the synergistic effect of ultrasound-targeted microbubble destruction (UTMD)-mediated Galectin-7-small interfering (si)RNA with the homing of BMSCs for AMI. The rat model of AMI was established, followed by identification of BMSCs. Rats with AMI received BMSC transplantation, BMSC transplantation + UTMD + siRNA negative control, or BMSC transplantation + UTMD + Galectin-7-siRNA. The cardiac function, hemodynamics indexes, degree of myocardial fiber injury and expression of apoptosis-related proteins in myocardial tissues of rats were detected. The homing of BMSCs was observed, and the indexes of myocardial microenvironment and the TGF-β/Smads pathway-related proteins in myocardial tissues were determined. AMI rats treated with UTMD-mediated Galectin-7-siRNA exhibited improved cardiac function and hemodynamics-related indices, decreased myocardial fiber injury and apoptotic cells, as well as enhanced homing ability of BMSCs, improved myocardial microenvironment, and suppressed TGF-β1/Smads pathway activation. In conclusion, the present study demonstrated that UTMD-mediated Galectin-7-siRNA treatment could enhance the homing ability of BMSCs, thus alleviating AMI in rats.

Research methodology for in vivo measurements of resting energy expenditure, daily body temperature, metabolic heat and non-viral tissue-specific gene therapy in baboons

A large number of studies have shown that the baboon is one of the most commonly used non-human primate (NHP) research model for the study of immunometabolic complex traits such as type 2 diabetes (T2D), insulin resistance (IR), adipose tissue dysfunction (ATD), dyslipidemia, obesity (OB) and cardiovascular disease (CVD). This paper reports on innovative technologies and advanced research strategies for energetics and translational medicine with this NHP model. This includes the following: measuring resting energy expenditure (REE) with the mobile indirect calorimeter Breezing®; monitoring daily body temperature using subcutaneously implanted data loggers; quantifying metabolic heat with veterinary infrared thermography (IRT) imaging, and non-viral non-invasive, tissue-specific ultrasound-targeted microbubble destruction (UTMD) gene-based therapy. These methods are of broad utility; for example, they may facilitate the engineering of ectopic overexpression of brown adipose tissue (BAT) mUCP-1 via UTMD-gene therapy into baboon SKM to achieve weight loss, hypophagia and immunometabolic improvement. These methods will be valuable to basic and translational research, and human clinical trials, in the areas of metabolism, cardiovascular health, and immunometabolic and infectious diseases.

Myocardium-targeted transplantation of PHD2 shRNA-modified bone mesenchymal stem cells through ultrasound-targeted microbubble destruction protects the heart from acute myocardial infarction

Ultrasound-targeted microbubble destruction (UTMD) is a promising approach to facilitate the precise delivery of bone marrow stem cells (BMSCs) to the ischemic myocardium. However, stem cell therapy for ischemic myocardium is challenging due to the poor survival of transplanted stem cells under severe ischemic conditions. In this study, we investigated whether myocardium-targeted transplantation of prolyl hydroxylase domain protein 2 (PHD2) shRNA-modified BMSCs by UTMD increases the viability of grafted cells, and enhances their cardioprotective effects in acute myocardial infarction. Methods: BMSCs were transduced with lentiviral PHD2 shRNA, and a novel microbubble formulation was prepared by a thin-film hydration method. In rats, BMSCs with or without PHD2 shRNA modification were transplanted by UTMD after inducing acute myocardium infarction. Effects of PHD2 shRNA on BMSC survival, myocardial apoptosis, angiogenesis, and cardiac function were evaluated. In vitro, anti-apoptotic effects and its mechanisms of PHD2 silencing on BMSC and BMSC-conditioned medium on H9C2 cell were detected. Results: PHD2 shRNA-modified BMSC transplantation by UTMD resulted in increased BMSC survival, reduced myocardial apoptosis, reduced infarct size, increased vascular density, and improved cardiac function compared to the control vector-modified BMSC transplantation by UTMD. PHD2 silencing increased BMSC survival through a HIF-1α-dependent mechanism. The decrease in cardiomyocyte apoptosis by conditioned medium from PHD2 shRNA-treated BMSCs was due to an increase in the expression of insulin-like growth factor (IGF)-1. Conclusions: The delivery of PHD2 shRNA-modified BMSCs by UTMD promoted grafted cell homing and activity, and increased myocardial angiogenesis in the infarcted heart, leading to improved cardiac function. This combination may provide a promising strategy for enhancing the effectiveness of stem cell therapy after acute myocardial infarction.

Applications of Ultrasound to Stimulate Therapeutic Revascularization

Many pathological conditions are characterized or caused by the presence of an insufficient or aberrant local vasculature. Thus, therapeutic approaches aimed at modulating the caliber and/or density of the vasculature by controlling angiogenesis and arteriogenesis have been under development for many years. As our understanding of the underlying cellular and molecular mechanisms of these vascular growth processes continues to grow, so too do the available targets for therapeutic intervention. Nonetheless, the tools needed to implement such therapies have often had inherent weaknesses (i.e., invasiveness, expense, poor targeting, and control) that preclude successful outcomes. Approximately 20 years ago, the potential for using ultrasound as a new tool for therapeutically manipulating angiogenesis and arteriogenesis began to emerge. Indeed, the ability of ultrasound, especially when used in combination with contrast agent microbubbles, to mechanically manipulate the microvasculature has opened several doors for exploration. In turn, multiple studies on the influence of ultrasound-mediated bioeffects on vascular growth and the use of ultrasound for the targeted stimulation of blood vessel growth via drug and gene delivery have been performed and published over the years. In this review article, we first discuss the basic principles of therapeutic ultrasound for stimulating angiogenesis and arteriogenesis. We then follow this with a comprehensive cataloging of studies that have used ultrasound for stimulating revascularization to date. Finally, we offer a brief perspective on the future of such approaches, in the context of both further research development and possible clinical translation.

A combination of ultrasound-targeted microbubble destruction with transplantation of bone marrow mesenchymal stem cells promotes recovery of acute liver injury

Background

Bone marrow mesenchymal stem cells (BMSCs) can provide an additional source of therapeutic stem cells for regeneration of liver cells during acute liver injury (ALI). However, the insufficient hepatic homing by the transplanted BMSCs limits their applications. Ultrasound-targeted microbubble destruction (UTMD) has been reported to promote the homing of transplanted stem cells into the ischemic myocardium. In this study, we investigated whether UTMD promotes the hepatic homing of BMSCs in ALI rats and evaluated the therapeutic effect.

Methods

BMSCs were isolated from the femurs and tibias of Sprague-Dawley (SD) rats. The isolated BMSCs were stably transfected with a lentivirus expressing enhanced green fluorescent protein (EGFP) that can be visualized and quantified in vivo after transplantation. Both tumor necrosis factor α (TNF-α) and stromal cell-derived factor 1 (SDF-1) were used to verify the appropriate ultrasound parameters. The ALI rats were divided into four groups: control, BMSCs, UTMD, and UTMD + BMSCs. The protein and mRNA expression levels of SDF-1, intercellular cell adhesion molecule (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), hepatocyte growth factor (HGF), and monocyte chemotactic protein 1 (MCP-1) in the exposed livers were analyzed at 48 h after treatment. ALI recovery was determined by serum biochemical parameters and histology.

Results

The isolated rat BMSCs demonstrated a good proliferation potential that was both osteogenic and adipogenic in differentiation and expressed cluster of differentiation (CD) 29 and CD90, but not CD45 or CD11b/c. After BMSC and/or UTMD treatment, the number of GFP-labeled BMSCs in the UTMD + BMSCs group was significantly higher than that of the BMSCs group (9.8 ± 2.3 vs. 5.2 ± 1.1/per high-power field). Furthermore, the expression of GFP mRNA was performed for evaluation of the homing rate of BMSCs in injury sites as well. In addition, the expression levels of SDF-1, ICAM-1, VCAM-1, HGF, and MCP-1 were higher (p < 0.01) in UTMD+BMSCs group. The serum levels of biomarkers were significantly lower in the UTMD + BMSCs group, and the apoptotic rate of hepatocytes in the UTMD + BMSCs group was markedly lower than that of the BMSCs group (all p < 0.05). The hepatic pathology was significantly alleviated in the UTMD + BMSCs group.

Conclusions

UTMD treatment efficiently induced a favorable microenvironment for cell engraftment, resulting in improvement of hepatic homing of BMSCs, which was probably mediated through upregulation of the expression of adhesion molecules and cytokines. UTMD treatment appeared to be an effective and noninvasive approach to achieve better efficacy of BMSC-based therapy for repairing a severely injured liver.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1098-4) contains supplementary material, which is available to authorized users.

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.

The future of collateral artery research

In the event of obstructive coronary artery disease, collateral arteries have been deemed an alternative blood source to preserve myocardial tissue perfusion and function. Monocytes play an important role in modulating this process, by local secretion of growth factors and extracellular matrix degrading enzymes. Extensive efforts have focused on developing compounds for augmenting the growth of collateral vessels (arteriogenesis). Nonetheless, clinical trials investigating the therapeutic potential of these compounds resulted in disappointing outcomes. Previous studies focused on developing compounds that stimulated collateral vessel growth by enhancing monocyte survival and activity. The limited success of these compounds in clinical studies, led to a paradigm shift in arteriogenesis research. Recent studies have shown genetic heterogeneity between CAD patients with sufficient and insufficient collateral vessels. The genetic predispositions in patients with poorly developed collateral vessels include overexpression of arteriogenesis inhibiting signaling pathways. New directions of arteriogenesis research focus on attempting to block such inhibitory pathways to ultimately promote arteriogenesis. Methods to detect collateral vessel growth are also critical in realizing the therapeutic potential of newly developed compounds. Traditional invasive measurements of intracoronary derived collateral flow index remain the gold standard in quantifying functional capacity of collateral vessels. However, advancements made in hybrid diagnostic imaging modalities will also prove to be advantageous in detecting the effects of pro-arteriogenic compounds.

An overview of the influence of therapeutic ultrasound exposures on the vasculature: high intensity ultrasound and microbubble-mediated bioeffects

It is well established that the interaction of ultrasound with soft tissues can induce a wide range of bioeffects. One of the most important and complex of these interactions in the context of therapeutic ultrasound is with the vasculature. Potential vascular effects range from enhancing microvascular permeability to inducing vascular damage and vessel occlusion. While aspects of these effects are broadly understood, the development of improved approaches to exploit these effects and gain a more detailed mechanistic understanding is ongoing and largely anchored in preclinical research. Here a general overview of this established yet rapidly evolving topic is provided, with a particular emphasis on effects arising from high-intensity focused ultrasound and microbubble-mediated exposures.

New progress in angiogenesis therapy of cardiovascular disease by ultrasound targeted microbubble destruction

Angiogenesis plays a vital part in the pathogenesis and treatment of cardiovascular disease and has become one of the hotspots that are being discussed in the past decades. At present, the promising angiogenesis therapies are gene therapy and stem cell therapy. Besides, a series of studies have shown that the ultrasound targeted microbubble destruction (UTMD) was a novel gene delivery system, due to its advantages of noninvasiveness, low immunogenicity and toxicity, repeatability and temporal and spatial target specificity; UTMD has also been used for angiogenesis therapy of cardiovascular disease. In this review, we mainly discuss the combination of UTMD and gene therapy or stem cell therapy which is applied in angiogenesis therapy in recent researches, and outline the future challenges and good prospects of these approaches.

Bone marrow mononuclear cells exert long-term neuroprotection in a rat model of ischemic stroke by promoting arteriogenesis and angiogenesis

Transplanted bone marrow-derived mononuclear cells (BMMNCs) can promote arteriogenesis and angiogenesis by incorporating into vascular walls and differentiating into smooth muscle cells (SMCs) and endothelial cells (ECs). Here, we explored whether BMMNCs can enhance arteriogenesis and angiogenesis and promote long-term functional recovery in a rat model of permanent middle cerebral artery occlusion (pMCAO). Sprague-Dawley rats were injected with vehicle or 1×10(7) BMMNCs labeled with BrdU via femoral vein 24 h after induction of pMCAO. Functional deficits were assessed weekly through day 42 after pMCAO, and infarct volume was assessed on day 7. We visualized the angioarchitecture by latex perfusion on days 14 and 42. BMMNC transplantation significantly reduced infarct volume and neurologic functional deficits compared with untreated or vehicle-treated ischemic groups. In BMMNC-treated rats, BrdU-positive cells were widely distributed in the infarct boundary zone, were incorporated into vessel walls, and enhanced the growth of leptomeningeal anastomoses, the circle of Willis, and basilar arteries. BMMNCs were shown to differentiate into SMCs and ECs from day 14 after stroke and preserved vascular repair function for at least 6 weeks. Our data indicate that BMMNCs can significantly enhance arteriogenesis and angiogenesis, reduce infarct volume, and promote long-term functional recovery after pMCAO in rats.

Ultrasound stimulation restores impaired neovascularization-related capacities of human circulating angiogenic cells

AIMS

Unsatisfactory effects of therapeutic angiogenesis in critical limb ischaemia may be ascribed to use of circulating angiogenic cells (CACs) derived from atherosclerotic patients with impaired neovascularization-related capacities. We tested whether ultrasound cell stimulation can restore the impaired capacities.

METHODS AND RESULTS

During culture of human peripheral blood-derived mononuclear cells for 4 days to achieve CACs, we stimulated the cells in culture daily with low-intensity pulsed ultrasound stimulation (LIPUS). Application of LIPUS to cells in culture derived from healthy volunteers augmented the generation and migration capacities of CACs, increased concentrations of angiopoietin 2 and nitrogen oxides in the culture medium, and increased the expression of phosphorylated-Akt and endothelial nitric oxide synthase in CACs on western blotting. Application of LIPUS to cells in culture derived from atherosclerotic patients also augmented the generation and migration capacities of CACs. Although neovascularization in the ischaemic hindlimb of athymic nude mice was impaired after intramuscular injection of CACs derived from atherosclerotic patients compared with that using CACs derived from healthy volunteers, LIPUS of the cells in culture derived from atherosclerotic patients restored the neovascularization capacities.

CONCLUSION

Therapeutic angiogenesis with LIPUS-pre-treated CACs may be a new strategy to rescue critical limb ischaemia in atherosclerotic patients.

Targeted delivery of bone mesenchymal stem cells by ultrasound destruction of microbubbles promotes kidney recovery in acute kidney injury

The aim of the present study was to explore whether ultrasound microbubble destruction augments site-targeted engraftment of bone marrow mesenchymal stem cells (BM-MSCs) to kidney tissue and promotes recovery of the kidney in acute kidney injury (AKI) in rats. AKI was induced by the subcutaneous injection of mercuric chloride (HgCl₂). Forty Sprague-Dawley (SD) rats were randomly divided into the following groups after the establishment of rat models of AKI (n = 10): (1) Model group alone (control group); (2) 1.0 W/cm² ultrasound (US) + microbubble (MB) (US/MB group); (3) MSCs group; and (4) 1.0 W/cm² US+MB + MSCs group (US/MB + MSCs group). The number of 4',6-diamidino-2-phenylindole (DAPI) labelled MSCs was evaluated by fluorescence microscopy and real-time polymerase chain reaction (RT-PCR) and Western blotting and histological examination were performed 7 days after MSCs transplantation. It was observed via fluorescence microscopy that the number of DAPI-labelled MSCs in the kidney for the US/MB + MSCs group was significantly more than the MSCs group (p < 0.05). The results from RT-PCR revealed that the US/MB and US/MB + MSCs groups markedly increased the level of inter-cellular adhesion molecule 1 (ICAM-1) messenger ribonucleic acid (mRNA) compared with the control group and the MSCs group (p < 0.05). Western blot analysis showed that the expression of hepatocyte growth factor (HGF) and epidermal growth factor (EGF) in the US/MB + MSCs group were markedly increased compared with the all other groups (p < 0.01). The extent of tubular necrosis and dilation was significantly milder in the US/MB + MSCs group (acoustic exposure conditions: 5s at 1 MHz and 1.0 W/cm² with a 5s pause, totalling 60 s) than the all other groups (p < 0.05). Microbubble destruction by 1.0 W/cm² ultrasound can promote both the homing of BM-MSCs to kidney tissue and the recovery of the kidney in AKI in rats.

Enhanced homing of mesenchymal stem cells to the ischemic myocardium by ultrasound-targeted microbubble destruction

In recent years, ultrasound-targeted microbubble destruction (UTMD) has been utilised for the targeted delivery of stem cells. We tested the effects of the myocardial micro-environment changes induced by UTMD on promoting the homing of mesenchymal stem cells (MSCs) to the ischemic myocardium. Dogs were randomly divided into two groups and treated with or without UTMD after the establishment of myocardial infarction models. 4,6-diamino-2-phenyl indole (DAPI) labelled MSCs were transplanted via coronary injections 2 weeks after myocardial infarction in both groups. The results from real-time PCR and western blot analyses indicated that the expression of various cytokines in UTMD-treated dogs was much higher than that observed in non-treated dogs. Histopathological findings demonstrate that ultrasound at a frequency of 1MHz and an intensity of 1.0W/cm(2) provoked inflammatory reactions with mild myocardial damage. Myocardial microenvironment changes caused by UTMD may promote the homing of MSCs to the ischemic myocardium. This non-invasive technique may be a promising method for cardiac cell transplantation therapy.

Ultrasound- and liposome microbubble-mediated targeted gene transfer to cardiomyocytes in vivo accompanied by polyethylenimine

OBJECTIVES

Gene transfer to cardiomyocytes in vivo has received much research attention in the last decade but remains a substantial hurdle. Gene transfer using ultrasound-targeted microbubble destruction is a promising tool for gene therapy. Little data have shown the feasibility and optimization of this method for primary myocardial disease. In this study, we sought to determine the feasibility and efficiency of in vivo gene transfer to the myocardium mediated by ultrasound-targeted microbubble destruction accompanied by polyethylenimine.

METHODS

Three plasmids (luciferase reporter, red fluorescent protein reporter, and enhanced green fluorescent protein reporter) were used in this study. The ultrasound parameters were also optimized. A solution containing phosphate-buffered saline, a plasmid, plasmid complex, or polyethylenimine/plasmid, and liposome microbubbles was injected via a tail vein with (study) or without (control) transthoracic ultrasound irradiation. The efficiency of reporter gene transfer was determined by detection of luciferase activity or microscopy, and histologic investigations of the tissue specimens were performed.

RESULTS

Ultrasound-targeted microbubble destruction significantly increased luciferase activity in vivo compared to plasmids and microbubbles alone (P < .001). More importantly, the increase in transgene expression was significantly related to ultrasound-targeted microbubble destruction in the presence of polyethylenimine (P < .001). In addition, fluorescein expression was present in all sections that received ultrasound-targeted microbubble destruction. The fluorescent reporter genes and luciferase plasmid all had similar results. Regardless of ultrasound exposure, expression in other organs was close to a background level except for the liver and lung. Hematoxylin-eosin staining showed no notable myocardial injury or death in control and treated mice.

CONCLUSIONS

An atraumatic targeted gene delivery technique based on ultrasound-targeted microbubble destruction and polyethylenimine has been developed to transfect cardiomyocytes in vivo. If a suitable target gene is added, the novel technique could be highly effective in many kinds of heart disease.

Covalently linking poly(lactic-co-glycolic acid) nanoparticles to microbubbles before intravenous injection improves their ultrasound-targeted delivery to skeletal muscle

Intravenously injected nanoparticles can be delivered to skeletal muscle through capillary pores created by the activation of microbubbles with ultrasound; however, strategies that utilize coinjections of free microbubbles and nanoparticles are limited by nanoparticle dilution in the bloodstream. Here, improvement in the delivery of fluorescently labeled ≈150 nm poly(lactic-co-glycolic acid) nanoparticles to skeletal muscle is attempted by covalently linking them to albumin-shelled microbubbles in a composite agent formulation. Studies are performed using an experimental model of peripheral arterial disease, wherein the right and left femoral arteries of BalbC mice are surgically ligated. Four days after arterial ligation, composite agents, coinjected microbubbles and nanoparticles, or nanoparticles alone are administered intravenously and 1 MHz pulsed ultrasound was applied to the left hindlimb. Nanoparticle delivery was assessed at 0, 1, 4, and 24 h post-treatment by fluorescence-mediated tomography. Within the coinjection group, both microbubbles and ultrasound are found to be required for nanoparticle delivery to skeletal muscle. Within the composite agent group, nanoparticle delivery is found to be enhanced 8- to 18-fold over 'no ultrasound' controls, depending on the time of measurement. A maximum of 7.2% of the initial nanoparticle dose per gram of tissue was delivered at 1 hr in the composite agent group, which was significantly greater than in the coinjection group (3.6%). It is concluded that covalently linking 150 nm-diameter poly(lactic-co-glycolic acid) nanoparticles to microbubbles before intravenous injection does improve their delivery to skeletal muscle.

"Smart" liposomal nanocontainers in biology and medicine

The perspectives of using liposomes for delivery of drugs to desired parts of the human body have been intensively investigated for more than 30 years. During this time many inventions have been suggested and different kinds of liposomal devices developed, and a number of them have reached the stages of preclinical or clinical trials. The latest techniques can be used to develop biocompatible nano-sized liposomal containers having some abilities of artificial intellect, such as the presence of sensory and responsive units. However, only a few have been clinically approved. Further improvements in this area depend on our knowledge of the interactions of drugs with the lipid bilayer of liposomes. Further studies on liposomal transport through the human body, their targeting of cells requiring therapeutic treatment, and finally, the development of techniques for controlled drug delivery to desired acceptors on cell surfaces or in cytoplasm are still required.

Focused ultrasound and microbubbles for enhanced extravasation

The permeability of blood vessels for albumin can be altered by using ultrasound and polymer or lipid-shelled microbubbles. The region in which the microbubbles were destroyed with focused ultrasound was quantified in gel phantoms as a function of pressure, number of cycles and type of microbubble. At 2MPa the destruction took place in a fairly wide area for a lipid-shelled agent, while for polymer-shelled agents at this setting, distinct destruction spots with a radius of only 1mm were obtained. When microbubbles with a thicker shell were used, the pressure above which the bubbles were destroyed shifts to higher values. In vivo both lipid and polymer microbubbles increased the extravasation of the albumin binding dye Evans Blue, especially in muscle leading to about 6-8% of the injected dose to extravasate per gram muscle tissue 30 min after start of the treatment, while no Evans Blue could be detected in muscle in the absence of microbubbles. Variation in the time between ultrasound treatment and Evans Blue injection, demonstrated that the time window for promoting extravasation is at least an hour at the settings used. In MC38 tumors, extravasation already occurred without ultrasound and only a trend towards enhancement with about a factor of 2 could be established with a maximum percentage injected dose per gram of 3%. Ultrasound mediated microbubble destruction especially enhances the extravasation in the highly vascularized outer part of the MC38 tumor and adjacent muscle and would, therefore, be most useful for release of, for instance, anti-angiogenic drugs.

Microbubbles as ultrasound triggered drug carriers

Originally developed as contrast agents for ultrasound imaging and diagnostics, in the past years, microbubbles have made their way back from the patients' bedside to the researcher's laboratory. Microbubbles are currently believed to have great potential as carriers for drugs, small molecules, nucleic acids, and proteins. This review provides insight into this intriguing new frontier from the perspective of the pharmaceutical scientist. First, basic aspects on the application of ultrasound-targeted microbubble destruction for drug delivery will be presented. Next, we will review the recently applied approaches for manufacturing and drug-loading microbubbles. Important quality issues and characterization techniques for advanced microbubble formulation will be discussed. Finally, we will provide an assessment of the prospects for microbubbles in drug and gene therapy, illustrating the problems and requirements for their future development.

Focused ultrasound-induced stimulation of microbubbles augments site-targeted engraftment of mesenchymal stem cells after acute myocardial infarction

Intravascular transplantation of bone marrow-derived mesenchymal stem cells (MSCs) is a promising therapeutic approach after acute myocardial infarction. Efficacy and targeting of myocardial cell engraftment are crucial variables determining the therapeutic value of MSC transplantation. Highly focused ultrasound-mediated stimulation of microbubbles (hf-UMS) allows locoregional pre-treatment of target tissue. In a "proof of concept" study, we investigated augmentation of site-targeted MSC engraftment with hf-UMS. We further evaluated the ability of transplanted MSCs to transmigrate across the endothelial barrier into non-ischemic and post-ischemic myocardium in vivo. After acute myocardial ischemia and reperfusion, rats received hf-UMS focused on the anterior left-ventricular wall followed by intravascular transplantation of MSCs. Global and regional myocardial engraftment of MSCs was quantified by means of confocal laser-scanning microscopy; endothelial adhesion, transendothelial migration and invasion of basement membrane were distinguished. Targeted myocardium exhibited higher amount of transplanted MSCs vs. non-targeted tissue. The rate of transendothelial migration was lowest in non-ischemic (41.2+/-2%) compared to post-ischemic myocardium (53+/-5.7%, p<0.01). Hf-UMS significantly increased the transmigration rate to 50+/-6.1% (p<0.05) and 64+/-8.9% (p<0.05), respectively. Additionally, myocardial segments exposed to hf-UMS revealed an onset of protease activity. Signs of undesired biological effects, such as induction of apoptosis and/or myocardial necrosis were not observed. This study provides the first evidence of the migration of MSCs across the myocardial endothelium in vivo. Hf-UMS not only improves myocardial engraftment of MSCs but also allows locoregional targeting of post-ischemic myocardium.

Optical microscopic findings of the behavior of perflubutane microbubbles outside and inside Kupffer cells during diagnostic ultrasound examination

PURPOSE

To investigate the behavior of perflubutane microbubbles outside and inside Kupffer cells during diagnostic ultrasound (US) examination, and to determine the thresholds of the acoustic pressure of different kinds of behavior.

METHODS

Acoustic behavior of perflubutane microbubbles inside and outside Kupffer cells in an acoustic field induced by a clinical US transducer and equipment was optically observed in vitro. The acoustic pressure was measured simultaneously by a calibrated hydrophone and an oscilloscope.

RESULTS

The acoustic behavior of microbubbles was optically categorized as stabilization, oscillation, transposition, shrinkage, and destruction. The mechanical index (MI) displayed on the US equipment correlated well with the acoustic pressure at the level of microbubbles measured hydrophonically. At a frame rate of 15 Hz with a frequency of 3.5 MHz and pulse repetition frequency of 3 KHz, the thresholds in term of MI for free microbubbles to begin oscillation, reach best oscillation, transposition, shrinkage, and destruction were 0.21, 0.44, 0.53, 0.75, and 1.03, respectively. Although adherent and phagocytosed microbubbles showed more stability enduring insonation compared with free microbubbles, the thresholds of shrinkage and destruction were MI 1.03 and 1.18 for adherent microbubbles, and 1.18 and 1.37 for phagocytosed microbubbles, respectively. Neither oscillation nor transposition of microbubbles inside Kupffer cells was observed microscopically. No cell damage because of microbubbles destruction was found in the present study.

CONCLUSION

Perflubutane microbubbles outside and inside Kupffer cells respond to external US insonation with same parameters of a clinical contrast-enhanced US study according to the acoustic pressure. Free microbubbles behave as stabilization, oscillation, transposition, shrinkage, and destruction under insonation. The adherent and phagocytosed microbubbles are more stable under insonation than free microbubbles, but still respond showing shrinkage and destruction when MI is over 1.03.

Randomized study of mononuclear bone marrow cell transplantation in patients with coronary surgery

BACKGROUND

Mononuclear bone marrow cell (MN-BMC) transplantation has great clinical potential to promote myocardiogenesis and angiogenesis. This randomized study was designed to assess the feasibility and safety of MN-BMC transplantation during coronary artery bypass grafting (CABG) in patients with ischemic heart failure.

METHODS

Thirty-six patients were prospectively enrolled and randomized to a MN-BMC group (n = 18) and a control group (n = 18). A mean number of 6.59 x 10(8) +/- 5.12 x 10(8) MN-BMC were injected into the infarcted and marginal areas during CABG in the MN-BMC group. The patients in the control group underwent CABG alone. All patients were followed up to 6 months.

RESULTS

There was one death in the MN-BMC group and no death in the control group. Two patients developed ventricular arrhythmia in the MN-BMC group. Compared with baseline and the control group, therapeutic effects of MN-BMC transplantation were observed over time. Heart function (New York Heart Association) was significantly improved and angina pectoris was alleviated in the MN-BMC group. Left ventricular ejection fraction in the MN-BMC group was greater than the control group. The thickness and motion velocity of the infarcted wall were significantly increased in the MN-BMC group. More pronounced perfusion improvements of ischemic regions and LV were observed in the MN-BMC group. There was one late death in the MN-BMC group. No procedure-related complications occurred.

CONCLUSIONS

MN-BMC transplantation improves cardiac function and regional perfusion in ischemic heart failure patients during CABG. A large cohort with long-term follow-up is needed to further evaluate the safety of MN-BMC transplantation.

Targeted delivery of nanoparticles bearing fibroblast growth factor-2 by ultrasonic microbubble destruction for therapeutic arteriogenesis

Therapeutic strategies in which recombinant growth factors are injected to stimulate arteriogenesis in patients suffering from occlusive vascular disease stand to benefit from improved targeting, less invasiveness, better growth-factor stability, and more sustained growth-factor release. A microbubble contrast-agent-based system facilitates nanoparticle deposition in tissues that are targeted by 1-MHz ultrasound. This system can then be used to deliver poly(D,L-lactic-co-glycolic acid) nanoparticles containing fibroblast growth factor-2 to mouse adductor muscles in a model of hind-limb arterial insufficiency. Two weeks after treatment, significant increases in both the caliber and total number of collateral arterioles are observed, indicating that the delivery of nanoparticles bearing fibroblast growth factor-2 by ultrasonic microbubble destruction may represent an effective and minimally invasive strategy for the targeted stimulation of therapeutic arteriogenesis.

Acoustic attenuation by contrast agent microbubbles in superficial tissue markedly diminishes petechiae bioeffects in deep tissue

OBJECTIVE

To measure how ultrasound attenuation by contrast agent microbubbles (MBs) in superficial tissue affects petechiae creation in underlying deep tissue.

MATERIALS AND METHODS

Studies using Sprague-Dawley rats were approved by the Animal Care and Use Committee. MBs were injected intravenously, and 12 ultrasound pulses (100 sinusoids of 1 MHz ultrasound per pulse) were applied through the skin overlying the hindlimb adductors at intervals of 10 or 60 seconds. In some groups, the skin was resected and immediately returned without re-establishing vascular connections. Muscle petechiae were counted.

RESULTS

Applying ultrasound through unperfused skin after bolus and continuous intravenous MB injection yielded, respectively, 30-fold and 3.5-fold more petechiae than for perfused skin. Surprisingly, petechiae/mm2 decreased with a higher MB dosage [0.12 +/- 0.05 (1 x 10 MBs/g) vs. 0.04 +/- 0.02 (3 x 10 MBs/g)] when ultrasound was applied through perfused skin. In contrast, petechiae/mm2 was approximately proportional to MB dosage for unperfused skin [0.17 +/- 0.10(5) (1 x 10 MBs/g) vs. 0.42 + 0.14 (3 x 10(5) MBs/g)]. In comparison to MB-free controls, MB solutions in this concentration range reduced the peak-negative pressure of ultrasound by 65% to 85%.

CONCLUSIONS

Acoustic attenuation by MBs in skin markedly reduces petechiae creation in deep muscle. Petechiae inhibition is dependent on [MB]2.1 and, therefore, dominates the otherwise proportional relationship between petechiae and [MB] in muscle. The drop of peak-negative pressure below a critical microvessel rupturing threshold is the probable mechanism for petechiae inhibition. These results indicate that high MB doses could, paradoxically, reduce the potential for petechiae creation and may have important bearing on the design of contrast ultrasound-based therapeutics.

Therapeutic opportunities in biological responses of ultrasound

The therapeutic benefits of several existing ultrasound-based therapies such as facilitated drug delivery, tumor ablation and thrombolysis derive largely from physical or mechanical effects. In contrast, ultrasound can also trigger various time-dependent biochemical responses in the exposed biological milieu. Several biological responses to ultrasound exposure have been previously described in the literature but only a handful of these provide therapeutic opportunities. These include the use of ultrasound for healing of soft tissues and bones, the use of ultrasound for inducing non-necrotic tumor atrophy as well as for potentiation of chemotherapeutic drugs, activation of the immune system, angiogenesis and suppression of phagocytosis. A review of these therapeutic opportunities is presented with particular emphasis on their mechanisms. Overall, this review presents the increasing importance of ultrasound's role as a biological sensitizer enabling novel therapeutic strategies.

Bone marrow cells recruited through the neuropilin-1 receptor promote arterial formation at the sites of adult neoangiogenesis in mice

Experimental and clinical evidence indicate that bone marrow cells participate in the process of new blood vessel formation. However, the molecular mechanisms underlying their recruitment and their exact role are still elusive. Here, we show that bone marrow cells are recruited to the sites of neoangiogenesis through the neuropilin-1 (NP-1) receptor and that they are essential for the maturation of the activated endothelium and the formation of arteries in mice. By exploiting adeno-associated virus vector-mediated, long-term in vivo gene expression, we show that the 165-aa isoform of VEGF, which both activates the endothelium and recruits NP-1+ myeloid cells, is a powerful arteriogenic agent. In contrast, neither the shortest VEGF121 isoform, which does not bind NP-1 and thus does not recruit bone marrow cells, nor semaphorin 3A, which attracts cells but inhibits endothelial activation, are capable of sustaining arterial formation. Bone marrow myeloid cells are not arteriogenic per se nor are they directly incorporated in the newly formed vasculature, but they contribute to arterial formation through a paracrine effect ensuing in the activation and proliferation of tissue-resident smooth muscle cells.

Microbubbles in ultrasound-triggered drug and gene delivery

Ultrasound contrast agents, in the form of gas-filled microbubbles, are becoming popular in perfusion monitoring; they are employed as molecular imaging agents. Microbubbles are manufactured from biocompatible materials, they can be injected intravenously, and some are approved for clinical use. Microbubbles can be destroyed by ultrasound irradiation. This destruction phenomenon can be applied to targeted drug delivery and enhancement of drug action. The ultrasonic field can be focused at the target tissues and organs; thus, selectivity of the treatment can be improved, reducing undesirable side effects. Microbubbles enhance ultrasound energy deposition in the tissues and serve as cavitation nuclei, increasing intracellular drug delivery. DNA delivery and successful tissue transfection are observed in the areas of the body where ultrasound is applied after intravascular administration of microbubbles and plasmid DNA. Accelerated blood clot dissolution in the areas of insonation by cooperative action of thrombolytic agents and microbubbles is demonstrated in several clinical trials.

Ultrasonic microbubble destruction stimulates therapeutic arteriogenesis via the CD18-dependent recruitment of bone marrow-derived cells

OBJECTIVE

We have previously shown that, under certain conditions, ultrasonic microbubble destruction creates arteriogenesis and angiogenesis in skeletal muscle. Here, we tested whether this neovascularization response enhances hyperemia in a rat model of arterial insufficiency and is dependent on the recruitment of bone marrow-derived cells (BMDCs) to treated tissues via a beta2 integrin (CD18)-dependent mechanism.

METHODS AND RESULTS

Sprague-Dawley rats, C57BL/6 wild-type mice, and C57BL/6 chimeric mice engrafted with BMDCs from either GFP+ or CD18-/- mice received bilateral femoral artery ligations. Microbubbles (MBs) were intravenously injected, and one gracilis muscle was exposed to pulsed 1 MHz ultrasound (US). Rat hindlimbs exhibited significant increases in adenosine-induced hyperemia and arteriogenesis compared to contralateral controls at 14 and 28 days posttreatment. US-MB-treated wild-type C57BL/6 mice exhibited significant arteriogenesis, angiogenesis, and CD11b+ monocyte recruitment; however, these responses were all completely blocked in CD18-/- chimeric mice. The number of BMDCs increased in US-MB-treated muscles of GFP+ chimeric mice; however, GFP+ BMDCs did not incorporate into microvessels as vascular cells.

CONCLUSIONS

In skeletal muscle affected by arterial occlusion, arteriogenesis and hyperemia can be significantly enhanced by ultrasonic MB destruction. This response depends on the recruitment, but not vascular incorporation, of BMDCs via a CD18-dependent mechanism.

Arteriogenesis: basic mechanisms and therapeutic stimulation

Pharmacological attempts to stimulate the growth of collateral arteries (arteriogenesis) are evolving towards a new treatment option for patients with vascular occlusive diseases. This enlargement of small pre-existing anastomoses towards large conductance arteries takes place independent of local oxygen tension and is driven by changes in luminal shear stress and infiltration of circulating cells. With the increasing knowledge regarding the distinct differences between capillary sprouting (angiogenesis) and arteriogenesis, several cytokines and growth factors have been demonstrated to stimulate the growth of arterial blood vessels in preclinical models of vascular disease. However, the translation towards clinical practice remains difficult and first in-man trials show limited success. Intensive research especially regarding new drug delivery platforms and the potentially serious side effects of pro-arteriogenic therapeutics is warranted before stimulation of arteriogenesis could become a significant treatment option for vascular occlusive diseases. This review focuses on the recent advances in the field of collateral artery growth. In addition, possible means to overcome the hurdles that have hampered the clinical implementation of pro-arteriogenic therapies will be discussed.

Therapeutic Arteriogenesis by Ultrasound-Mediated VEGF 165 Plasmid Gene Delivery to Chronically Ischemic Skeletal Muscle

Current methods of gene delivery for therapeutic angiogenesis are invasive, requiring either intraarterial or intramuscular administration. A noninvasive method of gene delivery has been developed using ultrasound-mediated destruction of intravenously administered DNA-bearing carrier microbubbles during their microcirculatory transit. Here we show that chronic ischemia could be markedly improved by ultrasound-mediated destruction of microbubbles bearing vascular endothelial growth factor-165 (VEGF(165)) plasmid DNA. Using a model of severe chronic hindlimb ischemia in rats, we demonstrated that ultrasound mediated VEGF(165)/green fluorescent protein (GFP) plasmid delivery resulted in a significant improvement in microvascular blood flow by contrast-enhanced ultrasound, and an increased vessel density by fluorescent microangiography, with minimal changes in control groups. The improvement in tissue perfusion was attributed predominantly to increases in noncapillary blood volume or arteriogenesis, with perfusion peaking at 14 days after delivery, followed by a partial regression of neovascularization at 6 weeks. Transfection was localized predominantly to the vascular endothelium of arterioles in treated ischemic muscle. RT-PCR confirmed the presence of VEGF(165)/GFP mRNA within treated ischemic muscle, being highest at day 3 postdelivery, and subsequently decreasing, becoming almost undetectable by 6 weeks. We found a modulation of endogenous growth factor expression in VEGF-treated ischemic muscle, consistent with a biologic effect of ultrasound mediated gene delivery. The results of our study demonstrate the utility of ultrasonic destruction of plasmid-bearing microbubbles to induce therapeutic arteriogenesis in the setting of severe chronic ischemia.

Gene therapy progress and prospects: Ultrasound for gene transfer

Ultrasound exposure (USE) in the presence of microbubbles (MCB) (e.g. contrast agents used to enhance ultrasound imaging) increases plasmid transfection efficiency in vitro by several orders of magnitude. Formation of short-lived pores in the plasma membrane ('sonoporation'), up to 100 nm in effective diameter lasting a few seconds, is implicated as the dominant mechanism, associated with acoustic cavitation. Ultrasound enhanced gene transfer (UEGT) has also been successfully achieved in vivo, with reports of spatially restricted and therapeutically relevant levels of transgene expression. Loading MCB with nucleic acids and/or disease-targeting ligands may further improve the efficiency and specificity of UEGT such that clinical testing becomes a realistic prospect.

Ultrasound-induced cavitation: applications in drug and gene delivery

Ultrasound, which has been conventionally used for diagnostics until recently, is now being extensively used for drug and gene delivery. This transformation has come about primarily due to ultrasound-mediated acoustic cavitation - particularly transient cavitation. Acoustic cavitation has been used to facilitate the delivery of small molecules, as well as macromolecules, including proteins and DNA. Controlled generation of cavitation has also been used for targeting drugs to diseased tissues, including skin, brain, eyes and endothelium. Ultrasound has also been employed for the treatment of several diseases, including thromboembolism, arteriosclerosis and cancer. This review provides a detailed account of mechanisms, current status and future prospects of ultrasonic cavitation in drug and gene delivery applications.