Ultrasonic Characteristics and Cellular Properties of Anabaena Gas Vesicles

Sound field and water quality in reservoirs using ultrasound as a management strategy to control cyanobacteria blooms

Ultrasound is an emerging technology for managing cyanobacteria harmful algal blooms (cHABs). This study characterized the sound field and water quality spatially at five field sites. Based on data from multiple sampling locations within a reservoir, the ultrasound signal attenuates exponentially with distance and the attenuation coefficient in the reservoirs is about ten times greater than pure water. The sound attenuation coefficients did not vary with frequency bandwidth or with turbidity, phycocyanin, temperature, or wind speed. Only chlorophyll-a had a positive relationship with the attenuation coefficient in the low frequency bandwidth. No statistically significant variation in the sound level was found when varying the measurement depth and ultrasound source depth, indicating that the sound field is even at the measured depths and ultrasound transducer configurations. Water quality paired with sound levels and compared to control reservoirs without ultrasound did not reveal significant differences in any of the reservoirs tested, suggesting there is no effect of ultrasound in the evaluated reservoirs. This field evaluation of ultrasound confirmed previous work indicating that cavitation, gas vesicle collapse, and critical structural resonance are unlikely to affect cHABs at the sound pressures and frequencies measured in the field.

Precise modulation of cell activity using sono-responsive nano-transducers

Ultrasound, as a form of mechanical energy, possesses a distinctive ability to deeply penetrate tissues, allowing for non-invasive manipulation of cellular activities. Utilizing nanomaterials in conjunction with ultrasound has enabled simple, efficient, spatiotemporally controllable, and minimally invasive regulation of cellular activities with ultrasound-generated electric, optical, acoustic, or chemical stimuli at the localized nanomaterials interface. This technology allows for precise and localized regulation of cellular activities, which is essential for studying and understanding complex biological processes, and also provides new opportunities for research, diagnostics, and therapeutics in the fields of biology and medicine. In this article, we review the state-of-the-art and ongoing developments in nanomaterials-enabled ultrasound cellular modulation, highlighting potential applications and advancements achieved through the integration of sono-responsive nanomaterials with ultrasound.

A Bioengineered Cathepsin B-sensitive Gas Vesicle Nanosystem That Responds With Increased Gray-level Intensity of Ultrasound Biomicroscopic Images

OBJECTIVE

This work aimed to promote the interaction of a modified gas vesicle (GV) with cathepsin B (CTSB) protease and analysed their backscattered signal by ultrasound (US).

METHODS

We modified the sequence of the gene coding for GvpC to contain a CTSB cleavage and expressed the protein in an Escherichia coli recombinant system. The protein was purified and added to GVs preparations in which the original GvpC was removed (ΔGV), constituting the modified GV (GV*). Western blot testing was used to compare GVs with GvpC and engineered GvpC at starting (T0) and after 24 h (T24) reacting with CTSB. A 21 MHz US B-mode and non-linear contrast mode (5% total power) imaged US phantoms having samples of GVwt, ΔGV (stripped GV), GV* and CTSB + GV*. Also, a 21 MHz US B-mode imaged US phantoms having a tumour cell line extracellular fraction (TCEF) and the TCEF + GV* sample. A 100% total US power was applied to collapse the GV structure.

RESULTS

On Western blotting, we detected a decrease in engineered GvpC levels 24 h after the incubation of GV* with CTSB, compared with the concentration at T0, suggesting that CTSB cleaved the engineered GvpC. Regions-of-interest over image of phantom cross-sections were determined and the B-mode image mean grey-level intensity resulted in a significant (p < 0.05) increase comparing CTSB + GV* with PBS (control), GVwt, ΔGV and GV*. Non-linear mode image grey-level intensity from CTSB + GV* increased by 11.79, 7.86 and 14.75 dB from samples containing GVwt, ΔGV and GV*, respectively. GV preparations incubated with TCEF and the TCEF + GV* sample showed an increase of 81% in signal compared with TCEF + GVwt.

CONCLUSION

The increased US backscattered signal intensity suggests GVs as a potential biosensor for protease activity, possibly aiding the detection of protease-rich tissue regions.

Advances in the application of gas vesicles in medical imaging and disease treatment

The gas vesicle (GV) is like a hollow nanoparticle consisting of an internal gas and a protein shell, which mainly consists of hydrophobic gas vesicle protein A (GvpA) and GvpC attached to the surface. GVs, first discovered in cyanobacteria, are mainly produced by photosynthetic bacteria (PSB) and halophilic archaea. After being modified and engineered, GVs can be utilized as contrast agents, delivery carriers, and immunological boosters for disease prevention, diagnosis, and treatment with good results due to their tiny size, strong stability and non-toxicity advantages. Many diagnostic and therapeutic approaches based on GV are currently under development. In this review, we discuss the source, function, physical and chemical properties of GV, focus on the current application progress of GV, and put forward the possible application prospect and development direction of GV in the future.

Nanobubble-actuated ultrasound neuromodulation for selectively shaping behavior in mice

Ultrasound is an acoustic wave which can noninvasively penetrate the skull to deep brain regions, enabling neuromodulation. However, conventional ultrasound's spatial resolution is diffraction-limited and low-precision. Here, we report acoustic nanobubble-mediated ultrasound stimulation capable of localizing ultrasound's effects to only the desired brain region in male mice. By varying the delivery site of nanobubbles, ultrasound could activate specific regions of the mouse motor cortex, evoking EMG signaling and limb movement, and could also, separately, activate one of two nearby deep brain regions to elicit distinct behaviors (freezing or rotation). Sonicated neurons displayed reversible, low-latency calcium responses and increased c-Fos expression in the sub-millimeter-scale region with nanobubbles present. Ultrasound stimulation of the relevant region also modified depression-like behavior in a mouse model. We also provide evidence of a role for mechanosensitive ion channels. Altogether, our treatment scheme allows spatially-targetable, repeatable and temporally-precise activation of deep brain circuits for neuromodulation without needing genetic modification.

Ultrasound-nanovesicles interplay for theranostics

Nanovesicles (NVs) are widely used in the treatment and diagnosis of diseases due to their excellent vascular permeability, good biocompatibility, high loading capacity, and easy functionalization. However, their yield and in vivo penetration depth limitations and their complex preparation processes still constrain their application and development. Ultrasound, as a fundamental external stimulus with deep tissue penetration, concentrated energy sources, and good safety, has been proven to be a patient-friendly and highly efficient strategy to overcome the restrictions of traditional clinical medicine. Recent research has shown that ultrasound can drive the generation of NVs, increase their yield, simplify their preparation process, and provide direct therapeutic effects and intelligent control to enhance the therapeutic effect of NVs. In addition, NVs, as excellent drug carriers, can enhance the targeting efficiency of ultrasound-based sonodynamic therapy or sonogenetic regulation and improve the accuracy of ultrasound imaging. This review provides a detailed introduction to the classification, generation, and modification strategies of NVs, emphasizing the impact of ultrasound on the formation of NVs and summarizing the enhanced treatment and diagnostic effects of NVs combined with ultrasound for various diseases.

Tracking adoptive natural killer cells via ultrasound imaging assisted with nanobubbles

The recent years has witnessed an exponential growth in the field of natural killer (NK) cell-based immunotherapy for cancer treatment. As a prerequisite to precise evaluations and on-demand interventions, the noninvasive tracking of adoptive NK cells plays a crucial role not only in post-treatment monitoring, but also in offering opportunities for preclinical studies on therapy optimizations. Here, we describe an NK cell tracking strategy for cancer immunotherapy based on ultrasound imaging modality. Nanosized ultrasound contrast agents, gas vesicles (GVs), were surface-functionalized to label NK cells. Unlike traditional microbubble contrast agents, nanosized GVs with their unique thermodynamical stability enable the detection of labeled NK cells under nonlinear contrast-enhanced ultrasound (nCEUS), without a noticeable impact on cellular viability or migration. By such labeling, we were able to monitor the trafficking of systematically infused NK cells to a subcutaneous tumor model. Upon co-treatment with interleukin (IL)-2, we observed a rapid enhancement in NK cell trafficking at the tumor site as early as 3 h post-infusion. Altogether, we show that the proposed ultrasound-based tracking strategy is able to capture the dynamical changes of cell trafficking in NK cell-based immunotherapy, providing referencing information for early-phase monotherapy evaluation, as well as understanding the effects of modulatory co-treatment. STATEMENT OF SIGNIFICANCE: In cellular immunotherapies, the post-infusion monitoring of the living therapeutics has been challenging. Several popular imaging modalities have been explored the monitoring of the adoptive immune cells, evaluating their trafficking and accumulation in the tumor. Here we demonstrated, for the first time, the ultrasound imaging-based immune cell tracking strategy. We showed that the acoustic labeling of adoptive immune cells was feasible with nanosized ultrasound contrast agents, overcoming the size and stability limitations of traditional microbubbles, enabling dynamical tracking of adoptive natural killer cells in both monotherapy and synergic treatment with cytokines. This article introduced the cost-effective and ubiquitous ultrasound imaging modality into the field of cellular immunotherapies, with broad prospectives in early assessment and on-demand image-guided interventions.

Gas-filled protein nanostructures as cavitation nuclei for molecule-specific sonodynamic therapy

Sonodynamic therapy (SDT) is a promising alternative for cancer therapy, understood to exert cytotoxicity through cavitation and subsequent production of large amounts of reactive oxygen species (ROS). Gas-filled protein nanostructures (gas vesicles or GVs) produced by cyanobacteria have a hollow structure similar to microbubbles and have demonstrated comparable enhancement of ultrasound imaging contrast. We thus hypothesized that GVs may act as stable nuclei for inertial cavitation to enhance SDT with improved enhanced permeability and retention (EPR) effects due to their nanometer scale. The function of GVs to mediate cavitation, ROS production, and cell-targeted toxicity under SDT was determined. In solution, we found that GVs successfully increased cavitation and enhanced ROS production in a dose- and time-dependent manner. Then, GV surfaces were modified (FGVs) to specifically target CD44⁺ cells and accumulate preferentially at the tumor site. In vitro sonodynamic therapy (SDT) showed ROS production and tumor cell toxicity substantially elevated in the presence of FGVs, and the addition of FGVs was found to enhance cavitation and subsequently inhibit tumor growth and exert greater damage to tumors under SDT in vivo. Our results thus demonstrate that FGVs can function as stable, nanosized, nuclei for spatially accurate and cell-targeted SDT. STATEMENT OF SIGNIFICANCE: The initiation of inertial cavitation is critical for ROS generation and subsequent cellular toxicity in SDT. Thus, precise control of the occurrence of cavitation is a key factor in increasing SDT's therapeutic efficacy. We explored nanometer-sized gas vesicles (GVs) as a new class of cavitation nuclei for molecule-specific sonodynamic therapy. Our results showed that GV-mediated SDT treatment enabled targeted disruption of specific cells expressing a known surface marker within the area of insonation, providing a spatially specific and targeted SDT treatment.

Acoustic scattering by gas-bearing cyanobacterium Microcystis: Modeling and in situ biomass assessment

Cyanobacterial harmful algal blooms (HABs) are increasing in a growing number of aquatic ecosystems around the world due to eutrophication and climatic change over the past few decades. Quantitative monitoring of HABs remains a challenge because their distributions are spatially heterogeneous and temporally variable. Most of the standard biological sampling methods are labor intensive and time consuming. In this paper, we present an efficient acoustic method to assess the biomass (biovolume) concentration of the cyanobacterium Microcystis in aquatic ecosystems. Acoustic backscattering vertical profiles from a gas-bearing Microcystis population were measured with echosounders at three frequencies (70, 120, and 333 kHz) in Lake Kinneret (case study). Concurrently, the volume concentration of Microcystis colonies and cyanobacteria-related Chlorophyll a were evaluated. We developed a partially coherent acoustic scattering model to quantify the cyanobacterium biomass based on depth-dependent acoustic backscattering signals. We also evaluated empirical regression models to obtain the Microcystis biomass from acoustically measured volume backscattering strength, S_v. It is demonstrated that both methods can convert the S_v to Microcystis biovolume concentrations reasonably well. Pro and cons of these methods are discussed. The results suggest that the presented methods may have a potential to be used for broader applications to monitor and quantify the gas-containing plankton in large aquatic ecosystems.

Precise Ultrasound Neuromodulation in a Deep Brain Region Using Nano Gas Vesicles as Actuators

Ultrasound is a promising new modality for non-invasive neuromodulation. Applied transcranially, it can be focused down to the millimeter or centimeter range. The ability to improve the treatment's spatial resolution to a targeted brain region could help to improve its effectiveness, depending upon the application. The present paper details a neurostimulation scheme using gas-filled nanostructures, gas vesicles (GVs), as actuators for improving the efficacy and precision of ultrasound stimuli. Sonicated primary neurons display dose-dependent, repeatable Ca²⁺ responses, closely synced to stimuli, and increased nuclear expression of the activation marker c-Fos in the presence of GVs. GV-mediated ultrasound triggered rapid and reversible Ca²⁺ responses in vivo and could selectively evoke neuronal activation in a deep-seated brain region. Further investigation indicate that mechanosensitive ion channels are important mediators of this effect. GVs themselves and the treatment scheme are also found not to induce significant cytotoxicity, apoptosis, or membrane poration in treated cells. Altogether, this study demonstrates a simple and effective method to achieve enhanced and better-targeted neurostimulation with non-invasive low-intensity ultrasound.

Applications of Bacterial Degrons and Degraders - Toward Targeted Protein Degradation in Bacteria

A repertoire of proteolysis-targeting signals known as degrons is a necessary component of protein homeostasis in every living cell. In bacteria, degrons can be used in place of chemical genetics approaches to interrogate and control protein function. Here, we provide a comprehensive review of synthetic applications of degrons in targeted proteolysis in bacteria. We describe recent advances ranging from large screens employing tunable degradation systems and orthogonal degrons, to sophisticated tools and sensors for imaging. Based on the success of proteolysis-targeting chimeras as an emerging paradigm in cancer drug discovery, we discuss perspectives on using bacterial degraders for studying protein function and as novel antimicrobials.

Protein nanoparticles in molecular, cellular, and tissue imaging

The quest to develop ideal nanoparticles capable of molecular, cellular, and tissue level imaging is ongoing. Since certain imaging probes and nanoparticles face drawbacks such as low aqueous solubility, increased ROS generation leading to DNA damage, apoptosis, and high cellular/organ toxicities, the development of versatile and biocompatible nanocarriers becomes necessary. Protein nanoparticles (PNPs) are one such promising class of nanocarriers that possess most of the desirable properties of an ideal nanocarrier for bioimaging applications. PNPs demonstrate high aqueous solubility, minimal cytotoxicity, and multi-cargo loading capacity. They are also amenable to surface-functionalization, as well as modulation of their hydrophobicity and hydrophilicity. The use of PNPs for bioimaging applications has made rapid advancements in the past two decades. Being comparatively less explored, the field opens up a plethora of opportunities and focus areas to engineer ideal bioimaging protein nanocarriers. The use of PNPs as carriers of their natural ligands as well as other heavy metals and fluorescent probes, along with drug molecules for combined theranostic applications has been reported. In addition, surface functionalization to impart specificity of targeting the PNPs has been shown to reduce nonspecific cellular interactions, thus reducing systemic toxicity. PNPs have been explored for their application in imaging of numerous cancers, cardiovascular diseases as well as imaging of the brain using near infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), X-ray computed tomography (CT), positron emission tomography (PET), single-photon emission computed tomography (SPECT), ultrasound (US), and photoacoustic (PA) imaging. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

The Advent of Biomolecular Ultrasound Imaging

Ultrasound imaging is one of the most widely used modalities in clinical practice, revealing human prenatal development but also arterial function in the adult brain. Ultrasound waves travel deep within soft biological tissues and provide information about the motion and mechanical properties of internal organs. A drawback of ultrasound imaging is its limited ability to detect molecular targets due to a lack of cell-type specific acoustic contrast. To date, this limitation has been addressed by targeting synthetic ultrasound contrast agents to molecular targets. This molecular ultrasound imaging approach has proved to be successful but is restricted to the vascular space. Here, we introduce the nascent field of biomolecular ultrasound imaging, a molecular imaging approach that relies on genetically encoded acoustic biomolecules to interface ultrasound waves with cellular processes. We review ultrasound imaging applications bridging wave physics and chemical engineering with potential for deep brain imaging.

Bloom-forming toxic cyanobacterium Microcystis: Quantification and monitoring with a high-frequency echosounder

Harmful cyanobacterial blooms pose a serious environmental threat to freshwater lakes and reservoirs. Investigating the dynamics of toxic bloom-forming cyanobacterial genus Microcystis is a challenging task due to its huge spatiotemporal heterogeneity. The hydroacoustic technology allows for rapid scanning of the water column synoptically and has a significant potential for rapid, non-invasive in situ quantification of aquatic organisms. The aim of this work is to develop a reliable cost-effective method for the accurate quantification of the biomass (B) of gas-bearing cyanobacterium Microcystis in water bodies using a high-frequency scientific echosounder. First, we showed that gas-bearing Microcystis colonies are much stronger backscatterers than gas-free phytoplanktonic algae. Then, in the tank experiments, we found a strong logarithmic relationship between the volume backscattering coefficient (s_v) and Microcystis B proxies, such as Microcystis-bound chlorophyll a (Chl a_Micro) and particle volume concentration. The s_v/B ratio remained unchanged over a wide range of B concentrations when the same source of Microcystis material was used. Our measurements in Lake Dianchi (China) also revealed strong logarithmic relationship between s_v and Chl a_Micro. The biomass-calibrated echosounder was used to study the diurnal variability of Microcystis B in the lake. We found a sharp increase in the cyanobacterium B and s_v/Chl a_Micro ratio near the water surface during the daytime and more uniform distribution of these parameters during the nighttime. We argue that the variations in B and s_v/Chl a_Micro ratio could be associated with temporal changes in thermal stratification and turbulent mixing. Our data suggest that the s_v/Chl a_Micro ratio positively correlates with (i) the percentage of larger colonies in population and/or (ii) the content of free gas in cells. The last properties allow Microcystis colonies to attain rapid floating, which enables them to concentrate at the water surface at conducive ambient conditions. The s_v/Chl a_Micro ratio can be a new important variable reflecting the ability of Microcystis colonies to migrate vertically. Monitoring of this ratio may help to determine the early warning threshold for Microcystis scum formation. The proposed acoustic technology for in situ quantification of Microcystis biomass can be a powerful tool for accurate monitoring and assessment of this cyanobacterium at high spatiotemporal resolution in water bodies.

Biogenic nanobubbles for effective oxygen delivery and enhanced photodynamic therapy of cancer

Tumor hypoxia is believed to be a factor limiting successful outcomes of oxygen-consuming cancer therapy, thereby reducing patient survival. A key strategy to overcome tumor hypoxia is to increase the prevalence of oxygen at the tumor site. Oxygen-containing microbubbles/nanobubbles have been developed to supply oxygen and enhance the effects of therapies such as radiotherapy and photodynamic therapy. However, the application of these bubbles is constrained by their poor stability, requiring major workarounds to increase their half-lives. In this study, we explore the potential of biogenic gas vesicles (GVs) as a new kind of oxygen carrier to alleviate tumor hypoxia. GVs, which are naturally formed, gas-filled, protein-shelled compartments, were modified on the surface of their protein shells by a layer of liposome. A substantial improvement of oxygen concentration was observed in hypoxic solution, in hypoxic cells, as well as in subcutaneous tumors when lipid-GVs(O₂) were added/tail-injected. Significant enhancement of tumor cell apoptosis and necrosis was also observed during photodynamic therapy (PDT) in the presence of lipid-GVs(O₂) both in vitro and in vivo. Lipid-GVs(O₂) alone induced no obvious change in cell viability in vitro or any apparent pathological abnormalities after mice were tail-injected with them. In all, lipid-GVs exhibited promising performance for intravenous gas delivery, enhanced PDT efficacy and low toxicity, a quality that may be applied to alleviate hypoxia in cancers, as well as hypoxia-related clinical treatments. STATEMENT OF SIGNIFICANCE: The development of stable oxygen-filled micro/nanobubbles capable of delivering oxygen to tumor sites is a major hurdle to enhancing the efficacy of cancer therapy. Currently, micro/nanobubbles are limited by their instability when oxygen is encapsulated, creating a large pressure gradient and surface tension. To improve stability, we modified the surfaces of GVs, a biogenic stable nanoscale hollow structure, as a new class of oxygen carriers. Lipid-coated GVs were found to be stable in solution and effective O₂ carriers. This will overcome the limitations of coalescence, short circulation time of synthetic bubbles during application. Our surface-modified GVs demonstrated low toxicity in vitro cell in vivo, while also being able to overcome hypoxia-associated therapy resistance when combined with photodynamic therapy.

Surface-modified GVs as nanosized contrast agents for molecular ultrasound imaging of tumor

Nanobubbles, as a kind of new ultrasound contrast agent (UCAs), have shown promise to penetrate tumor vasculature to allow for targeted imaging. However, their inherent physical instability is an ongoing concern that could weaken their imaging ability with ultrasound. Gas vesicles (GVs), which are genetically encoded, naturally stable nanostructures, have been developed as the first ultrasonic biomolecular reporters which showed strong contrast enhancement. However, further development of tumor imaging with GVs is limited by the quick clearance of GVs by the reticuloendothelial system (RES). Here, we developed PEGylated HA-GVs (PH-GVs) for in-tumor molecular ultrasound imaging by integrating polyethylene glycol (PEG) and hyaluronic acid (HA) in GV shells. PH-GVs were observed to accumulate around CD44-positive cells (SCC7) but not be internalized by macrophage cell line RAW 264.7. Green fluorescence from PH-GVs was found around cell nuclei in the tumor site after 6 h and the signal was sustained over 48 h following tail injection, demonstrating PH-GVs' ability to escape the clearance from the RES and to penetrate tumor vasculature through enhanced permeability and retention (EPR) effects. Further, PH-GVs produced strong ultrasound contrast in the tumor site in vivo, with no obvious side-effects detected following intravenous injection. Thus, we demonstrate the potential of PH-GVs as novel, nanosized and targeted UCAs for efficient and specific molecular tumor imaging, paving the way for the application of GVs in precise and personalized medicine.