Functional Activity and Endothelial-Lining Integrity of Ex Vivo Arteries Exposed to Ultrasound-Mediated Microbubble Destruction

The exact phenomenon and early signaling events of the endothelial cytoskeleton response to ultrasound

Low-intensity ultrasound can be applied for medical imaging and disease treatment in clinical and experimental studies. However, the biological effects of ultrasound on blood vessels, especially endothelial cells (ECs) are still unclear. In this study, the laws of endothelial cytoskeleton changes under ultrasound induction are investigated. ECs are exposed to low-intensity ultrasound, and the cytoskeletal morphology is analyzed by a filamentous (F)-actin staining technique. We further analyze the characteristics of cytoskeleton rupture using indirect immunofluorescence techniques and cytoskeleton electron microscopy. Finally, the biological effects induced by ultrasound at the tissue level are investigated in an ex vivo blood-vessel model. Significant changes in cytoskeletal structure are detected when induced by ultrasound, including cytoskeletal rupture, blebbing and apoptosis. Moreover, a temporal threshold of ECs injury under different ultrasonic intensities is established. This study illustrates a pattern of significant changes in the cytoskeletal structure of ECs induced by ultrasound. The finding serves as a guide for selecting a safe threshold for clinical ultrasound applications.

Caveolin Delivered by Ultrasound-Mediated Microbubble Destruction Prevents Endothelial Cell Proliferation

Introduction

The nitric oxide synthase (eNOS) is an important regulator of vascular homeostasis. eNOS is modulated by intracellular mechanisms that include protein-protein interaction with Caveolin-1 (Cav). Cav binds to and impairs eNOS activation reducing vascular permeability and angiogenesis. Blocking of eNOS by Cav has been proposed as therapeutic antiangiogenic approach. However, the efficient and controlled delivery of the peptide requires to be solved.

Methods

The effect of antennapedia (AP)-Cav loaded into microbubbles (MBs) and delivered by ultrasound-mediated microbubble destruction (UMMD) into brain endothelial cells (bEnd.3 cells) was evaluated on NO production using DAF2-DA, cell migration assessed by the wound healing assay, cell proliferation with BrdU, and ex-vivo angiogenesis in rat aortic rings.

Results

An enhanced inhibitory effect of AP-Cav was observed on cells treated with UMMD. MBs and ultrasound disruption delivery of AP-Cav increased acetylcholine-induced NO release, wound healing, cell proliferation, and angiogenesis inhibition on bEnd.3 cells, compared to free AP-Cav administration.

Conclusion

We demonstrated that the delivery of Cav via AP-Cav-loaded MBs and UMMD may be an administration method for Cav that would increase its therapeutic potential by enhancing efficacy and cellular specificity.

Targeted Microbubbles for Drug, Gene, and Cell Delivery in Therapy and Immunotherapy

Microbubbles are 1-10 μm diameter gas-filled acoustically-active particles, typically stabilized by a phospholipid monolayer shell. Microbubbles can be engineered through bioconjugation of a ligand, drug and/or cell. Since their inception a few decades ago, several targeted microbubble (tMB) formulations have been developed as ultrasound imaging probes and ultrasound-responsive carriers to promote the local delivery and uptake of a wide variety of drugs, genes, and cells in different therapeutic applications. The aim of this review is to summarize the state-of-the-art of current tMB formulations and their ultrasound-targeted delivery applications. We provide an overview of different carriers used to increase drug loading capacity and different targeting strategies that can be used to enhance local delivery, potentiate therapeutic efficacy, and minimize side effects. Additionally, future directions are proposed to improve the tMB performance in diagnostic and therapeutic applications.

Use of Nitric Oxide Donor-Loaded Microbubble Destruction by Ultrasound in Thrombus Treatment

In the presence of a vascular thrombus, the recovery of blood flow and vascular recanalization are very important to prevent tissue damage. An alternative procedure to thrombolysis is required for patients who are unable to receive surgery or thrombolytic drugs due to other physical conditions. Recently, the performance of thrombolysis combined with microbubbles has become an attractive and effective therapeutic procedure. Indeed, in a recent study, we demonstrated that, upon exposure to ultrasound, liposomes loaded with nitric oxide release agonists conjugated to microbubbles; therefore, there is potential to release the agonist in a controlled manner into specific tissues. This means that the effect of the agonist is potentiated, decreasing interactions with other tissues, and reducing the dose required to induce nitric-oxide-dependent vasodilation. In the present study, we hypothesized that a liposome microbubble delivery system can be used as a hydrophilic agonist carrier for the nitric oxide donor spermine NONOate, to elicit femoral vasodilation and clot degradation. Therefore, we used spermine-NONOate-loaded microbubbles to evaluate the effect of ultrasound-mediated microbubble disruption (UMMD) on thromboembolic femoral artery recanalization. We prepared spermine NONOate-loaded microbubbles and tested their effect on ex vivo preparations, hypothesizing that ultrasound-induced microbubble disruption is associated with the vasorelaxation of aortic rings. Thrombolysis was demonstrated in aorta blood-flow recovery after disruption by spermine NONOate-loaded microbubbles via ultrasound application in the region where the thrombus is located. Our study provides an option for the clinical translation of NO donors to therapeutic applications.

Localized Delivery of Caveolin-1 Peptide Assisted by Ultrasound-Mediated Microbubble Destruction Potentiates the Inhibition of Nitric Oxide-Dependent Vasodilation Response

In the endothelium, nitric oxide synthase (eNOS) is the enzyme that generates nitric oxide, a key molecule involved in a variety of biological functions and cancer-related events. Therefore, selective inhibition of eNOS represents an attractive therapeutic approach for NO-related diseases and anticancer therapy. Ultrasound-mediated microbubble destruction (UMMD) conjugated with cell-permeable peptides has been investigated as a drug delivery system for effective delivery of anticancer molecules. We investigated the feasibility of loading antennapedia-caveolin-1 peptide (AP-Cav), a specific eNOS inhibitor, onto microbubbles to be delivered by UMMD in rat aortic endothelium. AP-Cav-loaded microbubbles (AP-Cav-MBs) and US parameters were characterized. Aortas were treated with UMMD for 30 s with 1.3 × 10⁸ MBs/mL AP-Cav (8 μM)-MBs at 100-Hz pulse repetition frequency, 0.5-MPa acoustic pressure, 0.5 mechanical index and 10% duty cycle. NO-dependent vascular responses were assessed using an isolated organ system, 21 h post-treatment. Maximal relaxation response was inhibited 61.8% ± 1.6% in aortas treated with UMMD-AP-Cav-MBs, while in aortas treated with previously disrupted AP-Cav-MBs and then US, the inhibition was 31.6% ± 1.6%. The vascular contractile response was not affected. The impact of UMMD was evaluated in aortas treated with free AP-Cav; 30 μM of free AP-Cav was necessary to reach an inhibition response similar to that obtained with UMMD-AP-Cav-MBs. In conclusion, UMMD enhances the delivery and potentiates the effect of AP-Cav in the endothelial layer of rat aorta segments.

Release of vascular agonists from liposome-microbubble conjugate by ultrasound-mediated microbubble destruction: effect on vascular function

The endothelium is a single cell layer of the vessel wall and a key regulator of blood flow in vascular beds. Local and systemic pathologies have been associated with alterations in endothelial function. However, targeting the endothelium with vasoconstrictor or vasodilator drugs is often accompanied by systemic effects. Here, we evaluated a liposome-microbubble delivery system as a vascular hydrophilic agonist carrier. Phenylephrine (Phe) or acetylcholine (Ach)-loaded liposomes were conjugated to microbubbles. The drug release was triggered by ultrasound (US), and the vascular response was assessed in rat aortic rings using an isolated organ chamber. Aortic rings incubated with Phe-liposome-microbubble conjugate, exposed to US showed a marked contractile response (0.79 ± 0.04 g) compared to empty liposomes conjugated to microbubbles, aortic rings exposed only to US, and Phe-liposome-microbubble conjugate without US exposure that elicited a minimal or no response. Expressed as %, contractile responses were 85.24 ± 4.31% and 12.62 ± 3.23% for Phe-Chol-liposome-microbubble conjugate and empty Chol-liposome-microbubble conjugate exposed to US, respectively. Addition of 1 × 10^-5 M Ach to pre-contracted aortic rings decreased the contraction response from 1 to 0.21 g. The addition of Ach-liposome conjugate and exposure to US decreased the contraction response to 0.32 g. Additionally, the ED50 values for Phe and Ach released by US from liposome-microbubble conjugates were 3.6 × 10^-8 M ± 2.8 × 10^-9 M for Phe and 2.0 × 10^-8 M ± 1.8 × 10^-9 M. In conclusion, we evaluated a hybrid delivery system that consisted of loaded liposomes conjugated to microbubbles to deliver and release vascular agonists using UMMD.