Focused ultrasound-induced blood brain-barrier opening enhanced vascular permeability for GDNF delivery in Huntington's disease mouse model

Gene therapy for CNS disorders: modalities, delivery and translational challenges

Gene therapy is emerging as a powerful tool to modulate abnormal gene expression, a hallmark of most CNS disorders. The transformative potentials of recently approved gene therapies for the treatment of spinal muscular atrophy (SMA), amyotrophic lateral sclerosis (ALS) and active cerebral adrenoleukodystrophy are encouraging further development of this approach. However, most attempts to translate gene therapy to the clinic have failed to make it to market. There is an urgent need not only to tailor the genes that are targeted to the pathology of interest but to also address delivery challenges and thereby maximize the utility of genetic tools. In this Review, we provide an overview of gene therapy modalities for CNS diseases, emphasizing the interconnectedness of different delivery strategies and routes of administration. Important gaps in understanding that could accelerate the clinical translatability of CNS genetic interventions are addressed, and we present lessons learned from failed clinical trials that may guide the future development of gene therapies for the treatment and management of CNS disorders.

Recent advances of focused ultrasound induced blood-brain barrier opening for clinical applications of neurodegenerative diseases

With the aging population on the rise, neurodegenerative disorders have taken center stage as a significant health concern. The blood-brain barrier (BBB) plays an important role to maintain the stability of central nervous system, yet it poses a formidable obstacle to delivering drugs for neurodegenerative disease therapy. Various methods have been devised to confront this challenge, each carrying its own set of limitations. One particularly promising noninvasive approach involves the utilization of focused ultrasound (FUS) combined with contrast agents-microbubbles (MBs) to achieve transient and reversible BBB opening. This review provides a comprehensive exploration of the fundamental mechanisms behind FUS/MBs-mediated BBB opening and spotlights recent breakthroughs in its application for neurodegenerative diseases. Furthermore, it addresses the current challenges and presents future perspectives in this field.

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.

Blood-cerebrospinal fluid barrier opening by modified single pulse transcranial focused shockwave

Transcranial focused shockwave (FSW) is a novel noninvasive brain stimulation that can open blood-brain barriers (BBB) and blood-cerebrospinal fluid barriers (BCSFB) with a single low-energy (energy flux density 0.03 mJ/mm²) pulse and low-dose microbubbles (2 × 10⁶/kg). Similar to focused ultrasound, FSW deliver highly precise stimulation of discrete brain regions with adjustable focal lengths that essentially covers the whole brain. By opening the BCSFB, it allows for rapid widespread drug delivery to the whole brain by cerebrospinal fluid (CSF) circulation. Although no definite adverse effect or permeant injury was noted in our previous study, microscopic hemorrhage was infrequently observed. Safety concerns remain the major obstacle to further application of FSW in brain. To enhance its applicability, a modified single pulse FSW technique was established that present 100% opening rate but much less risk of adverse effect than previous methods. By moving the targeting area 2.5 mm more superficially on the left lateral ventricle as compared with the previous methods, the microscopic hemorrhage rate was reduced to zero. We systemically examine the safety profiles of the modified FSW-BCSFB opening regarding abnormal behavior and brain injury or hemorrhage 72 hr after 0, 1, and 10 pulses of FSW-treatment. Animal behavior, physiological monitor, and brain MRI were examined and recorded. Brain section histology was examined for hemorrhage, apoptosis, inflammation, oxidative stress related immunohistochemistry and biomarkers. The single pulse FSW group demonstrated no mortality or gross/microscopic hemorrhage (N = 30), and no observable changes in all examined outcomes, while 10 pulses of FSW was found to be associated with microscopic and temporary RBC extravasation (N = 6/30), and abnormal immunohistochemistry biomarkers which showed a trend of recovery at 72 hrs. The results suggest that single pulse low-energy FSW-BCSFB opening is effective, safe and poses minimal risk of injury to brain tissue (Sprague Dawley, SD rats).

ROS-generating alginate-coated gold nanorods as biocompatible nanosonosensitisers for effective sonodynamic therapy of cancer

Sonodynamic therapy (SDT) emerges as a promising non-invasive alternative for eradicating malignant tumours. However, its therapeutic efficacy remains limited due to the lack of sonosensitisers with high potency and biosafety. Previously, gold nanorods (AuNRs) have been extensively studied for their applications in photodynamic or photothermal cancer therapy, but their sonosensitising properties are largely unexplored. Here, we reported the applicability of alginate-coated AuNRs (AuNRs^ALG) with improved biocompatibility profiles as promising nanosonosensitisers for SDT for the first time. AuNRs^ALG were found stable under ultrasound irradiation (1.0 W/cm², 5 min) and maintained structural integrity for 3 cycles of irradiation. The exposure of the AuNRs^ALG to ultrasound irradiation (1.0 W/cm², 5 min) was shown to enhance the cavitation effect significantly and generate a 3 to 8-fold higher amount of singlet oxygen (¹O₂) than other reported commercial titanium dioxide nanosonosensitisers. AuNRs^ALG exerted dose-dependent sonotoxicity on human MDA-MB-231 breast cancer cells in vitro, with ∼ 81% cancer cell killing efficacy at a sub-nanomolar level (IC₅₀ was 0.68 nM) predominantly through apoptosis. The protein expression analysis showed significant DNA damage and downregulation of anti-apoptotic Bcl-2, suggesting AuNRs^ALG induced cell death through the mitochondrial pathway. The addition of mannitol, a reactive oxygen species (ROS) scavenger, inhibited cancer-killing effect of AuNRs^ALG-mediated SDT, further verifying that the sonotoxicity of AuNRs^ALG is driven by the production of ROS. Overall, these results highlight the potential application of AuNRs^ALG as an effective nanosonosensitising agent in clinical settings.

Intercellular Calcium Waves and Permeability Change Induced by Vertically Deployed Surface Acoustic Waves in a Human Cerebral Microvascular Endothelial Cell Line (hCMEC/D3) Monolayer

OBJECTIVE

The ultrasound-mediated blood-brain barrier (BBB) opening with microbubbles has been widely employed, while recent studies also indicate the possibility that ultrasound alone can open the BBB through a direct mechanical effect. However, the exact mechanisms through which ultrasound interacts with the BBB and whether it can directly trigger intracellular signaling and a permeability change in the BBB endothelium remain unclear.

METHODS

Vertically deployed surface acoustic waves (VD-SAWs) were applied on a human cerebral microvascular endothelial cell line (hCMEC/D3) monolayer using a 33-MHz interdigital transducer that exerts shear stress-predominant stimulation. The intracellular calcium response was measured by fluorescence imaging, and the permeability of the hCMEC/D3 monolayer was assessed by transendothelial electrical resistance (TEER).

DISCUSSION

At a certain intensity threshold, VD-SAWs induced an intracellular calcium surge that propagated to adjacent cells as intercellular calcium waves. VD-SAWs induced a TEER decrease in a pulse repetition frequency-dependent manner, thereby suggesting possible involvement of the mechanosensitive ion channels.

CONCLUSION

The unique VD-SAW system enables more physiological mechanical stimulation of the endothelium monolayer. Moreover, it can be easily combined with other measurement devices, providing a useful platform for further mechanistic studies on ultrasound-mediated BBB opening.

Recent Trend of Ultrasound-Mediated Nanoparticle Delivery for Brain Imaging and Treatment

In view of the fact that the blood-brain barrier (BBB) prevents the transport of imaging probes and therapeutic agents to the brain and thus hinders the diagnosis and treatment of brain-related disorders, methods of circumventing this problem (e.g., ultrasound-mediated nanoparticle delivery) have drawn much attention. Among the related techniques, focused ultrasound (FUS) is a favorite means of enhancing drug delivery via transient BBB opening. Photoacoustic brain imaging relies on the conversion of light into heat and the detection of ultrasound signals from contrast agents, offering the benefits of high resolution and large penetration depth. The extensive versatility and adjustable physicochemical properties of nanoparticles make them promising therapeutic agents and imaging probes, allowing for successful brain imaging and treatment through the combined action of ultrasound and nanoparticulate agents. FUS-induced BBB opening enables nanoparticle-based drug delivery systems to efficiently access the brain. Moreover, photoacoustic brain imaging using nanoparticle-based contrast agents effectively visualizes brain morphologies or diseases. Herein, we review the progress in the simultaneous use of nanoparticles and ultrasound in brain research, revealing the potential of ultrasound-mediated nanoparticle delivery for the effective diagnosis and treatment of brain disorders.

Nucleic acid therapies for CNS diseases: Pathophysiology, targets, barriers, and delivery strategies

Nucleic acid therapeutics have emerged as one of the very advanced and efficacious treatment approaches for debilitating health conditions, including those diseases affecting the central nervous system (CNS). Precise targeting with an optimal control over gene regulation confers long-lasting benefits through the administration of nucleic acid payloads via viral, non-viral, and engineered vectors. The current review majorly focuses on the development and clinical translational potential of non-viral vectors for treating CNS diseases with a focus on their specific design and targeting approaches. These carriers must be able to surmount the various intracellular and extracellular barriers, to ensure successful neuronal transfection and ultimately attain higher therapeutic efficacies. Additionally, the specific challenges associated with CNS administration also include the presence of blood-brain barrier (BBB), the complex pathophysiological and biochemical changes associated with different disease conditions and the existence of non-dividing cells. The advantages offered by lipid-based or polymeric systems, engineered proteins, particle-based systems coupled with various approaches of neuronal targeting have been discussed in the context of a variety of CNS diseases. The possibilities of rapid yet highly efficient gene modifications rendered by the breakthrough methodologies for gene editing and gene manipulation have also opened vast avenues of research in neuroscience and CNS disease therapy. The current review also underscores the extensive scientific efforts to optimize specialized, efficacious yet non-invasive and safer administration approaches to overcome the therapeutic delivery challenges specifically posed by the CNS transport barriers and the overall obstacles to clinical translation.

Blood-brain barrier (BBB)-on-a-chip: a promising breakthrough in brain disease research

The blood-brain barrier (BBB) represents a key challenge in developing brain-penetrating therapeutic molecules. BBB dysfunction is also associated with the onset and progression of various brain diseases. The BBB-on-a-chip (μBBB), an organ-on-chip technology, has emerged as a powerful in vitro platform that closely mimics the human BBB microenvironments. While the μBBB technology has seen wide application in the study of brain cancer, its utility in other brain disease models ("μBBB+") is less appreciated. Based on the advances of the μBBB technology and the evolution of in vitro models for brain diseases over the last decade, we propose the concept of a "μBBB+" system and summarize its major promising applications in pathological studies, personalized medical research, drug development, and multi-organ-on-chip approaches. We believe that such a sophisticated "μBBB+" system is a highly tunable and promising in vitro platform for further advancement of the understanding of brain diseases.

Delivering the Promise of Gene Therapy with Nanomedicines in Treating Central Nervous System Diseases

Central Nervous System (CNS) diseases, such as Alzheimer's diseases (AD), Parkinson's Diseases (PD), brain tumors, Huntington's disease (HD), and stroke, still remain difficult to treat by the conventional molecular drugs. In recent years, various gene therapies have come into the spotlight as versatile therapeutics providing the potential to prevent and treat these diseases. Despite the significant progress that has undoubtedly been achieved in terms of the design and modification of genetic modulators with desired potency and minimized unwanted immune responses, the efficient and safe in vivo delivery of gene therapies still poses major translational challenges. Various non-viral nanomedicines have been recently explored to circumvent this limitation. In this review, an overview of gene therapies for CNS diseases is provided and describes recent advances in the development of nanomedicines, including their unique characteristics, chemical modifications, bioconjugations, and the specific applications that those nanomedicines are harnessed to deliver gene therapies.

Ultrasound combined with glial cell line-derived neurotrophic factor-loaded microbubbles for the targeted treatment of drug addiction

Drug addiction is a serious problem globally, recently exacerbated by the COVID-19 pandemic. Glial cell-derived neurotrophic factor (GDNF) is considered a potentially effective strategy for the treatment of addiction. Previous animal experiments have proven that GDNF has a good therapeutic effect on drug addiction, but its clinical application is limited due to its poor blood-brain barrier (BBB) permeability. Low-frequency focused ultrasound, combined with microbubbles, is a non-invasive and reversible technique for locally-targeted BBB opening. In the present study, magnetic resonance imaging-guided low-frequency focused ultrasound, combined with GDNF microbubbles, was used to target BBB opening in the ventral tegmental area (VTA) region. The effects of GDNF on morphine-induced conditioned place preference (CPP) and acute withdrawal symptoms in rats after a partially opened BBB were evaluated by behavioral observation. Western blot was used to detect changes in tyrosine hydroxylase (TH) expression levels in the VTA region after different treatments, and high performance liquid chromatography was used to detect the changes in monoamine neurotransmitter content. The results showed that ultrasound combined with GDNF microbubbles targeted and opened the BBB in the VTA region, and significantly increased GDNF content, destroyed morphine-induced CPP, and reduced the withdrawal symptoms of morphine addiction in rats. Furthermore, the up-regulation of TH expression and the increase of norepinephrine and dopamine content induced by morphine were significantly reversed, and the increase of 5-hydroxytryptamine content was partially reversed. Therefore, ultrasound combined with GDNF microbubbles to target and open the BBB can effectively increase the content of central GDNF, thus playing a therapeutic role in morphine addiction. Our study provides a new approach to locally open the BBB and target delivery of neurotrophic factors, such as GDNF, to treat brain diseases like addiction.

Ultrasound-assisted brain delivery of nanomedicines for brain tumor therapy: advance and prospect

Nowadays, brain tumors are challenging problems, and the key of therapy is ensuring therapeutic drugs cross the blood-brain barrier (BBB) effectively. Although the efficiency of drug transport across the BBB can be increased by innovating and modifying nanomedicines, they exert insufficient therapeutic effects on brain tumors due to the complex environment of the brain. It is worth noting that ultrasound combined with the cavitation effect of microbubbles can assist BBB opening and enhance brain delivery of nanomedicines. This ultrasound-assisted brain delivery (UABD) technology with related nanomedicines (UABD nanomedicines) can safely open the BBB, facilitate the entry of drugs into the brain, and enhance the therapeutic effect on brain tumors. UABD nanomedicines, as the main component of UABD technology, have great potential in clinical application and have been an important area of interest in the field of brain tumor therapy. However, research on UABD nanomedicines is still in its early stages despite the fact that they have been associated with many disciplines, including material science, brain science, ultrasound, biology, and medicine. Some aspects of UABD theory and technology remain unclear, especially the mechanisms of BBB opening, relationship between materials of nanomedicines and UABD technology, cavitation and UABD nanomedicines design theories. This review introduces the research status of UABD nanomedicines, investigates their properties and applications of brain tumor therapy, discusses the advantages and drawbacks of UABD nanomedicines for the treatment of brain tumors, and offers their prospects. We hope to encourage researchers from various fields to participate in this area and collaborate on developing UABD nanomedicines into powerful tools for brain tumor therapy.

Focused Ultrasound-Induced Blood–Brain Barrier Opening Enhanced α-Synuclein Expression in Mice for Modeling Parkinson’s Disease

Parkinson’s disease (PD) is characterized by α-synuclein (αSNCA) aggregation in dopaminergic neurons. Gradual accumulation of αSNCA aggregates in substantia nigra (SN) diminishes the normal functioning of soluble αSNCA, leading to a loss of dopamine (DA) neurons. In this study, we developed focused ultrasound-targeted microbubble destruction (UTMD)-mediated PD model that could generate the disease phenotype via αSNCA CNS gene delivery. The formation of neuronal aggregates was analyzed with immunostaining. To evaluate the DA cell loss, we used tyrosine hydroxylase immunostaining and HPLC analysis on DA and its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This loss of DA was associated with a dose-dependent impairment in motor function, as assessed by the rotarod motor assessment. We demonstrate that UTMD-induced SNCA expression initiates αSNCA aggregation and results in a 50% loss of DA in SN. UTMD-related dose-dependent neuronal loss was identified, and it correlates with the degree of impairment of motor function. In comparison to chemical neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated and conventional intracerebral (IC)-injected animal models of PD, the UTMD-mediated αSNCA-based mouse model offers the advantage of mimicking the rapid development of the PD phenotype. The PD models that we created using UTMD also prove valuable in assessing specific aspects of PD pathogenesis and can serve as a useful PD model for the development of new therapeutic strategies.

A review of bioeffects induced by focused ultrasound combined with microbubbles on the neurovascular unit

Focused ultrasound combined with circulating microbubbles (FUS+MB) can transiently enhance blood-brain barrier (BBB) permeability at targeted brain locations. Its great promise in improving drug delivery to the brain is reflected by a rapidly growing number of clinical trials using FUS+MB to treat various brain diseases. As the clinical applications of FUS+MB continue to expand, it is critical to have a better understanding of the molecular and cellular effects induced by FUS+MB to enhance the efficacy of current treatment and enable the discovery of new therapeutic strategies. Existing studies primarily focus on FUS+MB-induced effects on brain endothelial cells, the major cellular component of BBB. However, bioeffects induced by FUS+MB expand beyond the BBB to cells surrounding blood vessels, including astrocytes, microglia, and neurons. Together these cell types comprise the neurovascular unit (NVU). In this review, we examine cell-type-specific bioeffects of FUS+MB on different NVU components, including enhanced permeability in endothelial cells, activation of astrocytes and microglia, as well as increased intraneuron protein metabolism and neuronal activity. Finally, we discuss knowledge gaps that must be addressed to further advance clinical applications of FUS+MB.

Liposome delivery to the brain with rapid short-pulses of focused ultrasound and microbubbles

Liposomes are clinically used drug carriers designed to improve the delivery of drugs to specific tissues while minimising systemic distribution. However, liposomes are unable to cross the blood-brain barrier (BBB) and enter the brain, mostly due to their large size (ca. 100 nm). A noninvasive and localised method of delivering liposomes across the BBB is to intravenously inject microbubbles and apply long pulses of ultrasound (pulse length: >1 ms) to a targeted brain region. Recently, we have shown that applying rapid short pulses (RaSP) (pulse length: 5 μs) can deliver drugs with an improved efficacy and safety profile. However, this was tested with a relatively smaller 3-kDa molecule (dextran). In this study, we examine whether RaSP can deliver liposomes to the murine brain in vivo. Fluorescent DiD-PEGylated liposomes were synthesized and injected intravenously alongside microbubbles. The left hippocampus of mice was then sonicated with either a RaSP sequence (5 μs at 1.25 kHz in groups of 10 ms at 0.5 Hz) or a long pulse sequence (10 ms at 0.5 Hz), with each pulse having a 1-MHz centre frequency (0.35 and 0.53 MPa). The delivery and distribution of the fluorescently-labelled liposomes were assessed by fluorescence imaging of the brain sections. The safety profile of the sonicated brains was assessed by histological staining. RaSP was shown to locally deliver liposomes across the BBB at 0.53 MPa with a more diffused and safer profile compared to the long pulse ultrasound sequence. Cellular uptake of liposomes was observed in neurons and microglia, while no uptake within astrocytes was observed in both RaSP and long pulse-treated brains. This study shows that RaSP allows a targeted and safe delivery of liposomal drugs into the murine brain with potential to deliver drugs into neuronal and glial targets.

Ultrasonic particles: An approach for targeted gene delivery

Gene therapy has been widely investigated for the treatment of genetic, acquired, and infectious diseases. Pioneering work utilized viral vectors; however, these are suspected of causing serious adverse events, resulting in the termination of several clinical trials. Non-viral vectors, such as lipid nanoparticles, have attracted significant interest, mainly due to their successful use in vaccines in the current COVID-19 pandemic. Although they allow safe delivery, they come with the disadvantage of off-target delivery. The application of ultrasound to ultrasound-sensitive particles allows for a direct, site-specific transfer of genetic materials into the organ/site of interest. This process, termed ultrasound-targeted gene delivery (UTGD), also increases cell membrane permeability and enhances gene uptake. This review focuses on the advances in ultrasound and the development of ultrasonic particles for UTGD across a range of diseases. Furthermore, we discuss the limitations and future perspectives of UTGD.

Cavitation-facilitated transmembrane permeability enhancement induced by acoustically vaporized nanodroplets

Ultrasound-facilitated transmembrane permeability enhancement has attracted broad attention in the treatment of central nervous system (CNS) diseases, by delivering gene/drugs into the deep site of brain tissues with a safer and more effective way. Although the feasibility of using acoustically vaporized nanodroplets to open the blood-brain-barrier (BBB) has previously been reported, the relevant physical mechanisms and impact factors are not well known. In the current study, a nitrocellulose (NC) membrane was used to mimic the multi-layered pore structure of BBB. The cavitation activity and the penetration ability of phase-changed nanodroplets were systemically evaluated at different concentration levels, and compared with the results obtained for SonoVue microbubbles. Passive cavitation detection showed that less intensified but more sustained inertial cavitation (IC) activity would be generated by vaporized nanodroplets than microbubbles. As the results, with a sufficiently high concentration (∼5 × 10⁸/mL), phase-changed nanodroplets were more effective than microbubbles in enabling a fluorescent tracer agent (FITC, 150 kDa) to penetrate deeper and more homogeneously through the NC membrane, and a positive correlation was observed between accumulated IC dose and the amount of penetrated FITC. In vivo studies further confirmed acoustically vaporized nanodroplets performed better than microbubbles by opening the BBB in rats' brains. These results indicated that phase-changed nanodroplets can be used as a safe, efficient and durable agent to achieve satisfactory cavitation-mediated permeability enhancement effect in biomedical applications.

Current knowledge and challenges associated with targeted delivery of neurotrophic factors into the central nervous system: focus on available approaches

During the last decades, numerous basic and clinical studies have been conducted to assess the delivery efficiency of therapeutic agents into the brain and spinal cord parenchyma using several administration routes. Among conventional and in-progress administrative routes, the eligibility of stem cells, viral vectors, and biomaterial systems have been shown in the delivery of NTFs. Despite these manifold advances, the close association between the delivery system and regeneration outcome remains unclear. Herein, we aimed to discuss recent progress in the delivery of these factors and the pros and cons related to each modality.

A single low-energy shockwave pulse opens blood-cerebrospinal fluid barriers and facilitates gastrodin delivery to alleviate epilepsy

The blood-cerebrospinal fluid barrier (BCSFB) is another gatekeeper between systemic circulation and the central nervous system (CNS), mainly present at the boundary between choroid plexuses and the ventricular system. This study demonstrates BCSFB opening in rats by single pulse of low-energy focused shockwave (FSW, energy flux density 0.03 mJ/mm², 2 × 10⁶ microbubbles/kg) treatment at lateral ventricle, resulting in significantly elevated cerebrospinal fluid (CSF) concentrations of systemically-administered gastrodin (GTD) (4 times vs. control within 3 hrs) that remained detectable for 24 hrs. The FSW-GTD group had significantly lower Racine's scale (<4) and zero mortality (n = 30) after lithium-pilocarpine-induced epilepsy. Electrophysiological recordings showed decreased epileptiform discharges, and brain section histology revealed reduced inflammation, oxidative stress and apoptosis, when compared with groups without FSW (Racine's scale: 4 ∼ 5; mortality: 26.67 ∼ 36.67%). FSW-mediated BCSFB opening provides a promising alternative for controlled-delivery of therapeutics into the CNS, offering rapid and widespread medication distribution. The technique could by applied in the development of novel therapies for various CNS diseases.

Early Detection and Reversal of Cell Apoptosis Induced by Focused Ultrasound-Mediated Blood-Brain Barrier Opening

Focused ultrasound (FUS) combined with microbubbles (MBs) has recently emerged as a potential approach to open the blood-brain barrier (BBB) for delivering drugs into the brain. However, appropriate approaches are still lacking to monitor the sublethal damage during FUS-mediated BBB opening in vivo, especially the early stage cell apoptotic events. Here, we developed a kind of nanoprobe-loaded MBs (AV-ICG-NPs@MBs) which can monitor the apoptotic cells that occur during FUS-mediated BBB opening through encapsulating the annexin V-targeted nanoprobes AV-ICG-NPs into the cavity of lipid-PLGA hybrid MBs. When irradiated by FUS, AV-ICG-NPs@MBs in the cerebral blood vessels would produce cavitation, favoring the BBB opening. Meanwhile, AV-ICG-NPs@MBs would be destroyed and release their AV-ICG-NPs payload. These released AV-ICG-NPs can be further delivered into the brain via the destructed BBB and bind with the phosphatidylserine externalized on the membrane of apoptotic cells if this occurs, leading to the prolonged detention of fluorescent signals in the brain. Furthermore, we also provided an effective strategy to inhibit or reverse the possible damage to the brain from a FUS-mediated BBB opening technology, through developing AV-ICG-NPs/GAS@MBs that encapsulate the antioxidant gastrodin (GAS) into AV-ICG-NPs@MBs. Accompanied by FUS irradiation and bubble cavitation, GAS was released and delivered into the brain, where they scavenged the oxygen free radicals produced from cavitation, leading to significantly lower fluorescence signals in the brain due to the absence of externalized phosphatidylserine. In conclusion, our study provides an approach to monitor and inhibit cell apoptotic events during FUS-mediated BBB opening.

Ultrasonic technologies in imaging and drug delivery

Ultrasonic technologies show great promise for diagnostic imaging and drug delivery in theranostic applications. The development of functional and molecular ultrasound imaging is based on the technical breakthrough of high frame-rate ultrasound. The evolution of shear wave elastography, high-frequency ultrasound imaging, ultrasound contrast imaging, and super-resolution blood flow imaging are described in this review. Recently, the therapeutic potential of the interaction of ultrasound with microbubble cavitation or droplet vaporization has become recognized. Microbubbles and phase-change droplets not only provide effective contrast media, but also show great therapeutic potential. Interaction with ultrasound induces unique and distinguishable biophysical features in microbubbles and droplets that promote drug loading and delivery. In particular, this approach demonstrates potential for central nervous system applications. Here, we systemically review the technological developments of theranostic ultrasound including novel ultrasound imaging techniques, the synergetic use of ultrasound with microbubbles and droplets, and microbubble/droplet drug-loading strategies for anticancer applications and disease modulation. These advancements have transformed ultrasound from a purely diagnostic utility into a promising theranostic tool.

Systemic manifestation and contribution of peripheral tissues to Huntington's disease pathogenesis

Huntington disease (HD) is an autosomal dominant neurodegenerative disease that is caused by expansion of cytosine/adenosine/guanine repeats in the huntingtin (HTT) gene, which leads to a toxic, aggregation-prone, mutant HTT-polyQ protein. Beyond the well-established mechanisms of HD progression in the central nervous system, growing evidence indicates that also peripheral tissues are affected in HD and that systemic signaling originating from peripheral tissues can influence the progression of HD in the brain. Herein, we review the systemic manifestation of HD in peripheral tissues, and the impact of systemic signaling on HD pathogenesis. Mutant HTT induces a body wasting syndrome (cachexia) primarily via its activity in skeletal muscle, bone, adipose tissue, and heart. Additional whole-organism effects induced by mutant HTT include decline in systemic metabolic homeostasis, which stems from derangement of pancreas, liver, gut, hypothalamic-pituitary-adrenal axis, and circadian functions. In addition to spreading via the bloodstream and a leaky blood brain barrier, HTT-polyQ may travel long distance via its uptake by neurons and its axonal transport from the peripheral to the central nervous system. Lastly, signaling factors that are produced and/or secreted in response to therapeutic interventions such as exercise or in response to mutant HTT activity in peripheral tissues may impact HD. In summary, these studies indicate that HD is a systemic disease that is influenced by intertissue signaling and by the action of pathogenic HTT in peripheral tissues. We propose that treatment strategies for HD should include the amelioration of HD symptoms in peripheral tissues. Moreover, harnessing signaling between peripheral tissues and the brain may provide a means for reducing HD progression in the central nervous system.

Focused Ultrasound Combined with Microbubbles in Central Nervous System Applications

The blood–brain barrier (BBB) protects the central nervous system (CNS) from invasive pathogens and maintains the homeostasis of the brain. Penetrating the BBB has been a major challenge in the delivery of therapeutic agents for treating CNS diseases. Through a physical acoustic cavitation effect, focused ultrasound (FUS) combined with microbubbles achieves the local detachment of tight junctions of capillary endothelial cells without inducing neuronal damage. The bioavailability of therapeutic agents is increased only in the area targeted by FUS energy. FUS with circulating microbubbles is currently the only method for inducing precise, transient, reversible, and noninvasive BBB opening (BBBO). Over the past decade, FUS-induced BBBO (FUS-BBBO) has been preclinically confirmed to not only enhance the penetration of therapeutic agents in the CNS, but also modulate focal immunity and neuronal activity. Several recent clinical human trials have demonstrated both the feasibility and potential advantages of using FUS-BBBO in diseased patients. The promising results support adding FUS-BBBO as a multimodal therapeutic strategy in modern CNS disease management. This review article explores this technology by describing its physical mechanisms and the preclinical findings, including biological effects, therapeutic concepts, and translational design of human medical devices, and summarizes completed and ongoing clinical trials.

Ternary Complexes of pDNA, Neuron-Binding Peptide, and PEGylated Polyethyleneimine for Brain Delivery with Nano-Bubbles and Ultrasound

In brain-targeted delivery, the transport of drugs or genes across the blood-brain barrier (BBB) is a major obstacle. Recent reports found that focused ultrasound (FUS) with microbubbles enables transient BBB opening and improvement of drug or gene delivery. We previously developed nano-sized bubbles (NBs), which were prepared based on polyethylene glycol (PEG)-modified liposomes containing echo-contrast gas, and showed that our NBs with FUS could also induce BBB opening. The aim of this study was to enhance the efficiency of delivery of pDNA into neuronal cells following transportation across the BBB using neuron-binding peptides. This study used the RVG-R9 peptide, which is a chimeric peptide synthesized by peptides derived from rabies virus glycoprotein and nonamer arginine residues. The RVG peptide is known to interact specifically with the nicotinic acetylcholine receptor in neuronal cells. To enhance the stability of the RVG-R9/pDNA complex in vivo, PEGylated polyethyleneimine (PEG-PEI) was also used. The ternary complexes composed of RVG-R9, PEG-PEI, and pDNA could interact with mouse neuroblastoma cells and deliver pDNA into the cells. Furthermore, for the in vivo experiments using NBs and FUS, gene expression was observed in the FUS-exposed brain hemispheres. These results suggest that this systemic gene delivery system could be useful for gene delivery across the BBB.

Innovative Applications of MR-Guided Focused Ultrasound for Neurological Disorders

Magnetic resonance-guided focused ultrasound (MRgFUS) is a cutting-edge technology that is changing the practice of movement disorders surgery. Given the noninvasive and innovative nature of this technology, there is great interest in expanding the use of MRgFUS to additional diseases and applications. Current approved applications target the motor thalamus to treat tremor, but clinical trials are exploring or plan to study noninvasive lesions with MRgFUS to ablate tumor cells in the brain as well as novel targets for movement disorders and brain regions associated with pain and epilepsy. Although there are additional potential indications for lesioning, the ability to improve function by destroying parts of the brain is still limited. However, MRgFUS can also be applied to a brain target after intravenous delivery of microbubbles to create cavitations and focally open the blood-brain barrier (BBB). This has already proven to be safe and technically feasible in human patients with Alzheimer's disease, and this action alone has potential to clear extracellular pathology associated with this and other neurodegenerative disorders. This also provides a foundation for noninvasive intravenous delivery of therapeutic molecules to precise brain targets after transient disruption of the BBB. Certain chemotherapies for brain tumors, immunotherapies, gene, and cell therapies are all examples of therapeutic or even restorative agents that normally will not enter the brain without direct infusion but which have been shown in preclinical studies to effectively traverse the BBB after transient disruption with MRgFUS. Here we will review these novel applications of MRgFUS to provide an overview of the extraordinary potential of this technology to expand future neurosurgical treatments of brain diseases.

Nanotechnology in neurosurgery: a systematic review

BACKGROUND

The application of nanotechnology in medicine encompasses an interdisciplinary field of sciences for the diagnosis, treatment, and monitoring of medical conditions. This study aims to systematically review and summarize the advances of nanotechnology applicable to neurosurgery.

METHODS

We performed a PubMed advanced search of reports exploring the advances of nanotechnology and nanomedicine relating to diagnosis, treatment, or both, in neurosurgery, for the last decade. The search was performed according to PRISMA guidelines, and the following data were extracted from each paper: title; authors; article type; PMID; DOI; year of publication; in vitro, in vivo model; nanomedical, nanotechnological material; nanofield; neurosurgical field; the application of the system; and main conclusions of the study.

RESULTS

A total of 78 original studies were included in this review. The results were organized into the following categories: functional neurosurgery, head trauma, neurodegenerative diseases, neuro-oncology, spinal surgery and peripheral nerves, vascular neurosurgery, and studies that apply to more than one field. A further categorization applied in terms of nanomedical field such as neuroimaging, neuro-nanotechnology, neuroregeneration, theranostics, and neuro-nanotherapy.

CONCLUSION

In reviewing the literature, significant advances in imaging and treatment of central nervous system diseases are underway and are expected to reach clinical practice in the next decade by the application of the rapidly evolving nanotechnology techniques.

Focused Ultrasound in Neuroscience. State of the Art and Future Perspectives

Transcranial MR-guided Focused ultrasound (tcMRgFUS) is a surgical procedure that adopts focused ultrasounds beam towards a specific therapeutic target through the intact skull. The convergence of focused ultrasound beams onto the target produces tissue effects through released energy. Regarding neurosurgical applications, tcMRgFUS has been successfully adopted as a non-invasive procedure for ablative purposes such as thalamotomy, pallidotomy, and subthalamotomy for movement disorders. Several studies confirmed the effectiveness of tcMRgFUS in the treatment of several neurological conditions, ranging from motor disorders to psychiatric disorders. Moreover, using low-frequencies tcMRgFUS systems temporarily disrupts the blood-brain barrier, making this procedure suitable in neuro-oncology and neurodegenerative disease for controlled drug delivery. Nowadays, tcMRgFUS represents one of the most promising and fascinating technologies in neuroscience. Since it is an emerging technology, tcMRgFUS is still the subject of countless disparate studies, even if its effectiveness has been already proven in many experimental and therapeutic fields. Therefore, although many studies have been carried out, many others are still needed to increase the degree of knowledge of the innumerable potentials of tcMRgFUS and thus expand the future fields of application of this technology.

Current Status and Challenges Associated with CNS-Targeted Gene Delivery across the BBB

The era of the aging society has arrived, and this is accompanied by an increase in the absolute numbers of patients with neurological disorders, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Such neurological disorders are serious costly diseases that have a significant impact on society, both globally and socially. Gene therapy has great promise for the treatment of neurological disorders, but only a few gene therapy drugs are currently available. Delivery to the brain is the biggest hurdle in developing new drugs for the central nervous system (CNS) diseases and this is especially true in the case of gene delivery. Nanotechnologies such as viral and non-viral vectors allow efficient brain-targeted gene delivery systems to be created. The purpose of this review is to provide a comprehensive review of the current status of the development of successful drug delivery to the CNS for the treatment of CNS-related disorders especially by gene therapy. We mainly address three aspects of this situation: (1) blood-brain barrier (BBB) functions; (2) adeno-associated viral (AAV) vectors, currently the most advanced gene delivery vector; (3) non-viral brain targeting by non-invasive methods.

Microbubbles and Nanobubbles with Ultrasound for Systemic Gene Delivery

The regulation of gene expression is a promising therapeutic approach for many intractable diseases. However, its use in clinical applications requires the efficient delivery of nucleic acids to target tissues, which is a major challenge. Recently, various delivery systems employing physical energy, such as ultrasound, magnetic force, electric force, and light, have been developed. Ultrasound-mediated delivery has particularly attracted interest due to its safety and low costs. Its delivery effects are also enhanced when combined with microbubbles or nanobubbles that entrap an ultrasound contrast gas. Furthermore, ultrasound-mediated nucleic acid delivery could be performed only in ultrasound exposed areas. In this review, we summarize the ultrasound-mediated nucleic acid systemic delivery system, using microbubbles or nanobubbles, and discuss its possibilities as a therapeutic tool.

Activation of Piezo1 by ultrasonic stimulation and its effect on the permeability of human umbilical vein endothelial cells

The acoustic radiation forces produced by ultrasonic stimulation induce shear stress on objects in the acoustic field. Piezo1, a mechanosensitive ion channel protein that is expressed on the plasma membranes of vertebrate cells, can sense shear stress and transduce it into downstream signaling. In this study, we examined the sensitivity of Piezo1 to ultrasonic stimulation and assessed its downstream biological functions in human umbilical vein endothelial cells (HUVECs). Ultrasonic stimulation using a stimulation power of 0.2 W and a frequency of 1 MHz for 10 s did not induce cell damage. However, ultrasonic stimulation induced an influx of calcium ions, which increased with an increase in the stimulation duration. Knockdown of Piezo1 protein decreased the influx of calcium ions during ultrasonic stimulation, which demonstrated that Piezo1 may be activated by the shear stress produced by ultrasonic stimulation. The influx of calcium ions in response to ultrasonic stimulation could be modulated by the Piezo1 protein level. Additionally, ultrasonic stimulation reduced the levels of downstream factors such as MLCK and ATP, which are involved in the Ca²⁺/CaM/MLCK pathway, by suppressing Piezo1. As the Ca²⁺/CaM/MLCK pathway influences the permeability of the cell membrane, the internalization of FITC-Dextran into cells under ultrasonic stimulation was validated. Ultrasonic stimulation was demonstrated to promote the increase in cell permeability, and the suppression of Piezo1 was shown to induce the decrease in cell permeability. Therefore, this study shows that ultrasonic stimulation may modulate the permeability of the membrane of HUVECs by modulating the expression of Piezo1 protein.

Preclinical Nanomedicines for Polyglutamine-Based Neurodegenerative Diseases

Polyglutamine (polyQ) diseases, such as Huntington's disease and several types of spinocerebellar ataxias, are dominantly inherited progressive neurodegenerative disorders and characterized by the presence of expanded CAG trinucleotide repeats in the respective disease locus of the patient genomes. Patients with polyQ diseases currently need to rely on symptom-relieving treatments because disease-modifying therapeutic interventions remain scarce. Many disease-modifying therapeutic agents are now under clinical testing for treating polyQ diseases, but their delivery to the brain is often too invasive (e.g., intracranial injection) or inefficient, owing to in vivo degradation and clearance by physiological barriers (e.g., oral and intravenous administration). Nanoparticles provide a feasible solution for improving drug delivery to the brain, as evidenced by an increasing number of preclinical studies that document the efficacy of nanomedicines for polyQ diseases over the past 5-6 years. In this review, we present the pathogenic mechanisms of polyQ diseases, the common animal models of polyQ diseases for evaluating the efficacy of nanomedicines, and the common administration routes for delivering nanoparticles to the brain. Next, we summarize the recent preclinical applications of nanomedicines for treating polyQ diseases and improving neurological conditions in vivo, placing emphasis on antisense oligonucleotides, small peptide inhibitors, and small molecules as the disease-modifying agents. We conclude with our perspectives of the burgeoning field of "nanomedicines for polyQ diseases", including the use of inorganic nanoparticles and potential drugs as next-generation nanomedicines, development of higher-order animal models of polyQ diseases, and importance of "brain-nano" interactions.

Helicid Reverses Lipopolysaccharide-Induced Inflammation and Promotes GDNF Levels in C6 Glioma Cells through Modulation of Prepronociceptin

Helicid suppresses inflammatory factors and protects nerve cells in the hippocampus of rats with depression, but the mechanisms underlying its protective effects are unclear at present. In this investigation, we conducted gene silencing, Helicid intervention and rescue experiments to explore the protective actions of PNOC, the prepronociceptin gene known to regulate inflammatory processes, and Helicid on a C6 cell model of inflammation induced by LPS. Collective data from Western blots, ELISA, immunofluorescence and flow cytometry experiments showed that PNOC silencing or administration of Helicid led to reduced inflammatory factor levels, oxidative stress and expression of glial fibrillary acidic protein (GFAP), along with increased glial cell lines-derived neurotrophic factor (GDNF) expression. Furthermore, expression of p-Akt in the Akt signaling pathway was increased. Interestingly, overexpression of PNOC in the Helicid treatment group partially reversed the Helicid-induced changes in the above biochemical indexes. Our collective results provide strong evidence of Helicid-mediated regulation of the Akt signaling pathway through PNOC to improve cell inflammation and oxidative stress.

Current insights on lipid nanocarrier-assisted drug delivery in the treatment of neurodegenerative diseases

The central nervous system (CNS) is vulnerable to pathologic processes that lead to the development of neurodegenerative disorders like Alzheimer's, Parkinson's and Huntington's diseases, Multiple sclerosis or Amyotrophic lateral sclerosis. These are chronic and progressive pathologies characterized by the loss of neurons and the formation of misfolded proteins. Additionally, neurodegenerative diseases are accompanied by a structural and functional dysfunction of the blood-brain barrier (BBB). Although serving as a protection for the CNS, the existence of physiological barriers, especially the BBB, limits the access of several therapeutic agents to the brain, constituting a major hindrance in neurotherapeutics advancement. In this regard, nanotechnology-based approaches have arisen as a promising strategy to not only improve drug targeting to the brain, but also to increase bioavailability. Lipid nanocarriers such as liposomes, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), microemulsions and nanoemulsions, have already proven their potential for enhancing brain transport, crossing more easily into the CNS and allowing the administration of medicines that could benefit the treatment of neurological pathologies. Given the socioeconomic impact of such conditions and the advent of nanotechnology that inevitably leads to more effective and superior therapeutics for their management, it is imperative to constantly update on the current knowledge of these topics. Herein, we provide insight on the BBB and the pathophysiology of the main neurodegenerative disorders. Moreover, this review seeks to highlight the several approaches that can be used to improve the delivery of therapeutic agents to the CNS, while also offering an extensive overview of the latest efforts regarding the use of lipid-based nanocarriers in the management of neurodegenerative diseases.

Recent Advances in the Use of Focused Ultrasound for Magnetic Resonance Image-Guided Therapeutic Nanoparticle Delivery to the Central Nervous System

Targeting systemically-administered drugs and genes to specific regions of the central nervous system (CNS) remains a challenge. With applications extending into numerous disorders and cancers, there is an obvious need for approaches that facilitate the delivery of therapeutics across the impervious blood-brain barrier (BBB). Focused ultrasound (FUS) is an emerging treatment method that leverages acoustic energy to oscillate simultaneously administered contrast agent microbubbles. This FUS-mediated technique temporarily disrupts the BBB, allowing ordinarily impenetrable agents to diffuse and/or convect into the CNS. Under magnetic resonance image guidance, FUS and microbubbles enable regional targeting—limiting the large, and potentially toxic, dosage that is often characteristic of systemically-administered therapies. Subsequent to delivery across the BBB, therapeutics face yet another challenge: penetrating the electrostatically-charged, mesh-like brain parenchyma. Non-bioadhesive, encapsulated nanoparticles can help overcome this additional barrier to promote widespread treatment in selected target areas. Furthermore, nanoparticles offer significant advantages over conventional systemically-administered therapeutics. Surface modifications of nanoparticles can be engineered to enhance targeted cellular uptake, and nanoparticle formulations can be tailored to control many pharmacokinetic properties such as rate of drug liberation, distribution, and excretion. For instance, nanoparticles loaded with gene plasmids foster relatively stable transfection, thus obviating the need for multiple, successive treatments. As the formulations and applications of these nanoparticles can vary greatly, this review article provides an overview of FUS coupled with polymeric or lipid-based nanoparticles currently utilized for drug delivery, diagnosis, and assessment of function in the CNS.