Echographic and physical characterization of albumin-stabilized nanobubbles

Intracranial Gene Delivery Mediated by Albumin-Based Nanobubbles and Low-Frequency Ultrasound

Research in the field of high-intensity focused ultrasound (HIFU) for intracranial gene therapy has greatly progressed over the years. However, limitations of conventional HIFU still remain. That is, genes are required to cross the blood-brain barrier (BBB) in order to reach the neurological disordered lesion. In this study, we introduce a novel direct intracranial gene delivery method, bypassing the BBB using human serum albumin-based nanobubbles (NBs) injected through a less invasive intrathecal route via lumbar puncture, followed by intracranial irradiation with low-frequency ultrasound (LoFreqUS). Focusing on both plasmid DNA (pDNA) and messenger RNA (mRNA), our approach utilizes LoFreqUS for deeper tissue acoustic penetration and enhancing gene transfer efficiency. This drug delivery method could be dubbed as the "Spinal Back-Door Approach", an alternative to the "front door" BBB opening method. Experiments showed that NBs effectively responded to LoFreqUS, significantly improving gene transfer in vitro using U-87 MG cell lines. In vivo experiments in mice demonstrated significantly increased gene expression with pDNA; however, we were unable to obtain conclusive results using mRNA. This novel technique, combining albumin-based NBs and LoFreqUS offers a promising, efficient, targeted, and non-invasive solution for central nervous system gene therapy, potentially transforming the treatment landscape for neurological disorders.

LB, Endo H, Itaka K, Tachibana K. Efficient mRNA Delivery with Lyophilized Human Serum Albumin-Based Nanobubbles

In this study, we developed an efficient mRNA delivery vehicle by optimizing a lyophilization method for preserving human serum albumin-based nanobubbles (HSA-NBs), bypassing the need for artificial stabilizers. The morphology of the lyophilized material was verified using scanning electron microscopy, and the concentration, size, and mass of regenerated HSA-NBs were verified using flow cytometry, nanoparticle tracking analysis, and resonance mass measurements, and compared to those before lyophilization. The study also evaluated the response of HSA-NBs to 1 MHz ultrasound irradiation and their ultrasound (US) contrast effect. The functionality of the regenerated HSA-NBs was confirmed by an increased expression of intracellularly transferred Gluc mRNA, with increasing intensity of US irradiation. The results indicated that HSA-NBs retained their structural and functional integrity markedly, post-lyophilization. These findings support the potential of lyophilized HSA-NBs, as efficient imaging, and drug delivery systems for various medical applications.

Nanobubble technologies: Applications in therapy from molecular to cellular level

Nanobubbles are gaseous entities suspended in bulk liquids that have widespread beneficial usage in many industries. Nanobubbles are already proving to be versatile in furthering the effectiveness of disease treatment on cellular and molecular levels. They are functionalized with biocompatible and stealth surfaces to aid in the delivery of drugs. At the same time, nanobubbles serve as imaging agents due to the echogenic properties of the gas core, which can also be utilized for controlled and targeted delivery. This review provides an overview of the biomedical applications of nanobubbles, covering their preparation and characterization methods, discussing where the research is currently focused, and how they will help shape the future of biomedicine.

Influence of Nanobubble Size Distribution on Ultrasound-Mediated Plasmid DNA and Messenger RNA Gene Delivery

The use of nanobubbles (NBs) for ultrasound-mediated gene therapy has recently attracted much attention. However, few studies have evaluated the effect of different NB size distribution to the efficiency of gene delivery into cells. In this study, various size of albumin stabilized sub-micron bubbles were examined in an in vitro ultrasound (1 MHz) irradiation setup in the aim to compare and optimize gene transfer efficiency. Results with pDNA showed that gene transfer efficiency in the presence of NB size of 254.7 ± 3.8 nm was 2.5 fold greater than those with 187.3 ± 4.8 nm. Similarly, carrier-free mRNA transfer efficiency increased in the same conditions. It is suggested that NB size greater than 200 nm contributed more to the delivery of genes into the cytoplasm with ultrasound. Although further experiments are needed to understand the underlying mechanism for this phenomenon, the present results offer valuable information in optimizing of NB for future ultrasound-mediate gene therapy.

Perfluoropentane-filled chitosan poly-acrylic acid nanobubbles with high stability for long-term ultrasound imaging in vivo

Reducing the size of ultrasound contrast agents (UCAs) will decrease the intensity of the ultrasound echogenic signals and reduce the stability of the bubbles. Therefore, it is a challenge to design nanobubbles that are less than 200 nm in size and that have both good imaging abilities and high stability for long-term imaging in vivo. In this work, we successfully prepared perfluoropentane-filled chitosan poly-acrylic acid (PFP-CS-PAA) nanobubbles with a size of about 100 nm via a direct simple core-template-free strategy. In vitro tests demonstrated that the nanobubbles showed satisfactory imaging capabilities in non-linear harmonic imaging mode and had significantly better stability than commercial Sonovue® lipid microbubbles. It was valuable to discover that the prepared PFP-CS-PAA nanobubbles could exhibit good imaging quality in rat livers for 10 min after intravenous injection. Also, the PFP-CS-PAA nanobubbles could maintain imaging capabilities in nude mouse tumors for 7 days after intratumoral injection, which indicated that these nanobubbles could keep their stability for a long time in vivo. To the best of our knowledge, the ultrasound imaging persistence time in vivo was the longest of currently reported polymer nanobubbles that are smaller than 200 nm. This new nanosized UCA with high stability has great potential for long-term ultrasound imaging in vivo. Tumor cellular uptake and histological analysis revealed that PFP-CS-PAA nanobubbles could be taken up into tumor cells, but no intracellular uptake was observed in the case of Sonovue®. Animal fluorescence imaging in vivo demonstrated that PFP-CS-PAA nanobubbles could be effectively cleared after intravenous injection within 168 h. MTT assays indicated that PFP-CS-PAA nanobubbles had appropriate biocompatibility. Abnormal levels of blood urea nitrogen were detected after the intravenous administration of PFP-CS-PAA nanobubbles to rats, and body-weight gain was inhibited for up to 6 d, but, after that, body weights recovered their tendency to increase.

Nanobubble Mediated Gene Delivery in Conjunction With a Hand-Held Ultrasound Scanner

Recent research has revealed that nanobubbles (NBs) can be an effective tool for gene transfection in conjunction with therapeutic ultrasound (US). However, an approach to apply commercially available hand-held diagnostic US scanners for this purpose has not been evaluated as of now. In the present study, we first compared in vitro, the efficiency of gene transfer (pCMV-Luciferase) with lipid-based and albumin-based NBs irradiated by therapeutic US (1MHz, 5.0 W/cm²) in oral squamous carcinoma cell line HSC-2. Secondly, we similarly examined if gene transfer in mice is possible using a clinical hand-held US scanner (2.3MHz, MI 1.0). Results showed that lipid-based NBs induced more gene transfection compared to albumin-based NBs, in vitro. Furthermore, significant gene transfer was also obtained in mice liver with lipid-based NBs. Sub-micro sized bubbles proved to be a powerful gene transfer reagent in combination with conventional hand-held ultrasonic diagnostic device.