Transient Disruption Of Blood-brain Barrier Research Articles

Intraosseous administration into the skull: Potential blood-brain barrier bypassing route for brain drug delivery.

Progress in treating central nervous system (CNS) disorders is retarded owing to a limited understanding of brain disease pathology. Additionally, the blood-brain barrier (BBB) limits molecular entry into the brain. Many approaches for brain drug delivery to overcome the BBB, such as BBB permeability enhancement, transient BBB disruption, and direct surgical administration have been explored with limited success. Recent research has shown that direct vascular channels exist between the skull bone marrow and the meninges, allowing myeloid and lymphoid cells to migrate. We hypothesized that these direct channels may also allow brain drug delivery from the skull bone marrow to the brain. In this study, for the first time we propose intraosseous administration of drugs into the skull (intracalvariosseous [ICO]) as a novel approach for brain drug delivery via BBB bypassing routes. We tested the feasibility of the approach by applying nine representative compounds over thinned mouse skulls to simulate ICO and measuring the compound entry level in the brain compared to that after systemic administration. Surprisingly, we found that the skull is not completely impermeable to drug penetration into the brain and the tested compounds reached the brain tissue several tens-to-hundred times higher by ICO than systemic application. These findings suggest a role for the BBB bypassing route from skull to brain, apart from the systemic route, in the drug entry into the brain after ICO. This approach should be applicable to other CNS drugs and even BBB impermeable drugs. Overall ICO provides an innovative and advantageous pathway for effective treatment of brain diseases.

The Bradykinin B2 Receptor Agonist (NG291) Causes Rapid Onset of Transient Blood-Brain Barrier Disruption Without Evidence of Early Brain Injury.

Background: The blood–brain barrier (BBB) describes the brain’s highly specialized capillaries, which form a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, by preventing the entry of potentially harmful circulating molecules into the brain. However, this specialized function is challenging for the development of CNS therapeutics. Several strategies to facilitate drug delivery into the brain parenchyma via disruption of the BBB have been proposed. Bradykinin has proven effective in disrupting mechanisms across the blood–tumor barrier. Unfortunately, bradykinin has limited therapeutic value because of its short half-life and the undesirable biological activity elicited by its active metabolites.Objective: To evaluate NG291, a stable bradykinin analog, with selective agonist activity on the bradykinin-B2 receptor and its ability to disrupt the BBB transiently.Methods: Sprague Dawley rats and CD-1 mice were subjected to NG291 treatment (either 50 or 100 μg/kg, intravenously). Time and dose-dependent BBB disruption were evaluated by histological analysis of Evans blue (EB) extravasation. Transcellular and paracellular BBB leakage were assessed by infiltration of 99mTc-albumin (66.5 KDa) and 14C-sucrose (340 Da) radiolabeled probes into the brains of CD-1 mice treated with NG291. NG291 influence on P-glycoprotein (P-gp) efflux pump activity was evaluated by quantifying the brain accumulation of 3H-verapamil, a known P-gp substrate, in CD-1 mice.Results: NG291-mediated BBB disruption was localized, dose-dependent, and reversible as measured by EB extravasation. 99mTc-albumin leakage was significantly increased by 50 μg/kg of NG291, whereas 100 μg/kg of NG291 significantly augmented both 14C-sucrose and 99mTc-albumin leakage. NG291 enhanced P-gp efflux transporter activity and was unable to increase brain uptake of the P-gp substrate pralidoxime. NG291 did not evoke significant short-term neurotoxicity, as it did not increase brain water content, the number of Fluoro-Jade C positive cells, or astrocyte activation.Conclusion: Our findings strongly suggest that NG291 increases BBB permeability by two different mechanisms in a dose-dependent manner and increases P-gp efflux transport. This increased permeability may facilitate the penetration into the brain of therapeutic candidates that are not P-gp substrates.

Status Quo and Trends of Intra-Arterial Therapy for Brain Tumors: A Bibliometric and Clinical Trials Analysis.

Intra-arterial drug delivery circumvents the first-pass effect and is believed to increase both efficacy and tolerability of primary and metastatic brain tumor therapy. The aim of this update is to report on pertinent articles and clinical trials to better understand the research landscape to date and future directions. Elsevier’s Scopus and ClinicalTrials.gov databases were reviewed in August 2021 for all possible articles and clinical trials of intra-arterial drug injection as a treatment strategy for brain tumors. Entries were screened against predefined selection criteria and various parameters were summarized. Twenty clinical trials and 271 articles satisfied all inclusion criteria. In terms of articles, 201 (74%) were primarily clinical and 70 (26%) were basic science, published in a total of 120 different journals. Median values were: publication year, 1986 (range, 1962–2021); citation count, 15 (range, 0–607); number of authors, 5 (range, 1–18). Pertaining to clinical trials, 9 (45%) were phase 1 trials, with median expected start and completion years in 2011 (range, 1998–2019) and 2022 (range, 2008–2025), respectively. Only one (5%) trial has reported results to date. Glioma was the most common tumor indication reported in both articles (68%) and trials (75%). There were 215 (79%) articles investigating chemotherapy, while 13 (65%) trials evaluated targeted therapy. Transient blood–brain barrier disruption was the commonest strategy for articles (27%) and trials (60%) to optimize intra-arterial therapy. Articles and trials predominately originated in the United States (50% and 90%, respectively). In this bibliometric and clinical trials analysis, we discuss the current state and trends of intra-arterial therapy for brain tumors. Most articles were clinical, and traditional anti-cancer agents and drug delivery strategies were commonly studied. This was reflected in clinical trials, of which only a single study had reported outcomes. We anticipate future efforts to involve novel therapeutic and procedural strategies based on recent advances in the field.

Non-invasive gene delivery across the blood-brain barrier: present and future perspectives.

Non-invasive gene delivery across the blood-brain barrier: present and future perspectives.

Electroporation-Based Therapy for Brain Tumors: A Review.

Electroporation-based therapy (EBT), as a high-voltage-pulse technology has been prevalent with favorable clinical outcomes in the treatment of various solid tumors. This review paper aims to promote the clinical translation of EBT for brain tumors. First, we briefly introduced the mechanism of pore formation in a cell membrane activated by external electric fields using a single cell model. Then, we summarized and discussed the current in vitro and in vivo preclinical studies, in terms of (1) the safety and effectiveness of EBT for brain tumors in animal models, and (2) the blood-brain barrier (BBB) disruption induced by EBT. Two therapeutic effects could be achieved in EBT for brain tumors simultaneously, i.e., the tumor ablation induced by irreversible electroporation (IRE) and transient BBB disruption induced by reversible electroporation (RE). The BBB disruption could potentially improve the uptake of antitumor drugs thereby enhancing brain tumor treatment. The challenges that hinder the application of EBT in the treatment of human brain tumors are discussed in the review paper as well.

Removal of a compressive mass causes a transient disruption of blood-brain barrier but a long-term recovery of spiny stellate neurons in the rat somatosensory cortex.

In the cranial cavity, a space-occupying mass such as epidural hematoma usually leads to compression of brain. Removal of a large compressive mass under the cranial vault is critical to the patients. The purpose of this study was to examine whether and to what extent epidural decompression of the rat primary somatosensory cortex affects the underlying microvessels, spiny stellate neurons and their afferent fibers. Rats received epidural decompression with preceding 1-week compression by implantation of a bead. The thickness of cortex was measured using brain coronal sections. The permeability of blood-brain barrier (BBB) was assessed by Evans Blue and immunoglobulin G extravasation. The dendrites and dendritic spines of the spiny stellate neurons were revealed by Golgi-Cox staining and analyzed. In addition, the thalamocortical afferent (TCA) fibers in the cortex were illustrated using anterograde tracing and examined. The cortex gradually regained its thickness over time and became comparable to the sham group at 3 days after decompression. Although the diameter of cortical microvessels were unaltered, a transient disruption of the BBB was observed at 6 hours and 1 day after decompression. Nevertheless, no brain edema was detected. In contrast, the dendrites and dendritic spines of the spiny stellate neurons and the TCA fibers were markedly restored from 2 weeks to 3 months after decompression. Epidural decompression caused a breakdown of the BBB, which was early-occurring and short-lasting. In contrast, epidural decompression facilitated a late-onset and prolonged recovery of the spiny stellate neurons and their afferent fibers.

The Bradykinin B2 Receptor Agonist NG291 Causes Rapid, Transient Blood‐Brain Barrier Disruption Without Evidence of Persistent Brain Injury: Implications for Drug Delivery to the Brain.

The blood brain barrier (BBB) is a term used to describe the highly specialized capillaries of the brain which forms a dynamic interface that maintains central nervous system (CNS) homeostasis. The BBB supports the CNS, in part, through its barrier functions which prevent entry of potentially harmful circulating molecules into the brain. However, the barrier activities of the BBB are also an obstacle to the delivery of therapeutics to the brain. One strategy to facilitate the delivery of therapeutics into the brain is to transiently induce BBB disruption. Bradykinins are one class of molecule produced endogenously and contribute to transient BBB disruption through agonist activity on the bradykinin B2 receptor (B2R).Unfortunately, the endogenous peptide bradykinin is of little therapeutic value because of its short half‐life and because it also activates the bradykinin B1 receptor that generates an exaggerated inflammatory response. We have been studying NG291, a physiologically stable bradykinin analogue that has selective agonist activity on B2R, and its ability to disrupt the BBB. Sprague Dawley (SD) rats and CD‐1 mice were subjected to NG291 treatment (either 50μg/Kg or 100μg/Kg, IV). BBB disruption was measured by Evans blue extravasation in SD rats in a time and dose dependent fashion. Disruption was evaluated in mice using the large and small sized radioactive tracers 99mTc‐Albumin (66.5KDa) and 14C‐Sucrose (340Da), respectively. We evaluated the potential harm of NG291 administration in rats via changes in brain water content and detection of cellular death via Fluoro‐Jade C staining. Evans blue studies in rats confirmed that NG291 is disrupting the BBB in a time and dose dependent fashion with the BBB regaining function 2hr after 50μg/Kg and 4hr after 100μg/Kg of NG291 administration. In mice, both albumin and sucrose tissue/serum ratio were significantly increased within 15 minutes of NG291 injection vs vehicle controls. We have observed no increased cell death nor change in water content in groups treated with NG291 when compared to saline injected controls. We conclude that NG291 has the potential to acutely disrupt the BBB, generating a window where potential CNS therapies can be more effectively delivered to the brain. This has the potential to speed up drug development process, increase the number of CNS therapies that reach the market, and help those in dire need of such treatments.

THER-04. THE USE OF AN ADENOSINE A2 AGONIST TO IMPROVE THE PREVENTION AND TREATMENT OF BRAIN METASTASES

As systemic therapies for cancer become increasingly effective, there is generally a rise in the incidence of brain metastases as a site of first recurrence. This occurs because most antineoplastic agents do not reach the brain in therapeutic concentrations. Many approaches have been studied to improve drug distribution to the central nervous system (CNS) such as intra-arterial administration, osmotic blood-brain barrier (BBB) disruption, focused ultrasound, convection-enhanced delivery, development of CNS penetrant pro-drugs, and the use of vasoactive peptides to transiently disrupt the BBB. However, none of these has improved the prevention or treatment of CNS metastases. Regadenoson is an adenosine A2 agonist that is FDA approved for use in cardiac stress tests. In animals, it has been shown to transiently increase BBB permeability allowing high molecular weight dextran and chemotherapy to enter brain in higher concentrations. A clinical study designed to determine if regadenoson will perform similarly in humans has been CTEP approved and will soon be accruing patients through the Adult Brain Tumor Consortium. If the results are encouraging, future studies will focus on administering regadenoson concurrently with systemically administered chemotherapy in an effort to reduce the incidence of CNS metastases and to improve CNS drug delivery in patients with known brain metastases. This presentation will focus on the available pre-clinical and clinical data supporting this approach and the potential advantages and risks associated with transient BBB disruption in this setting.

Safety and Feasibility of Repeated and Transient Blood-Brain Barrier Disruption by Pulsed Ultrasound in Patients with Recurrent Glioblastoma.

The blood-brain barrier (BBB) limits the efficacy of drug therapies for glioblastoma (GBM). Preclinical data indicate that low-intensity pulsed ultrasound (LIPU) can transiently disrupt the BBB and increase intracerebral drug concentrations. A first-in-man, single-arm, single-center trial (NCT02253212) was initiated to investigate the transient disruption of the BBB in patients with recurrent GBM. Patients were implanted with a 1-MHz, 11.5-mm diameter cranial ultrasound device (SonoCloud-1, CarThera). The device was activated monthly to transiently disrupt the BBB before intravenous carboplatin chemotherapy. Between 2014 and 2016, 21 patients were registered for the study and implanted with the SonoCloud-1; 19 patients received at least one sonication. In 65 ultrasound sessions, BBB disruption was visible on T1w MRI for 52 sonications. Treatment-related adverse events observed were transient and manageable: a transient edema at H1 and at D15. No carboplatin-related neurotoxicity was observed. Patients with no or poor BBB disruption (n = 8) visible on MRI had a median progression-free survival (PFS) of 2.73 months, and a median overall survival (OS) of 8.64 months. Patients with clear BBB disruption (n = 11) had a median PFS of 4.11 months, and a median OS of 12.94 months. SonoCloud-1 treatments were well tolerated and may increase the effectiveness of systemic drug therapies, such as carboplatin, in the brain without inducing neurotoxicity.See related commentary by Sonabend and Stupp, p. 3750.

Transient blood–brain barrier disruption is induced by low pulsed electrical fields in vitro: an analysis of permeability and trans-endothelial electric resistivity

The blood–brain barrier (BBB) is limiting transcellular and paracellular movement of molecules and cells, controls molecular traffic, and keeps out toxins. However, this protective function is the major hurdle for treating brain diseases such as brain tumors, Parkinson’s disease, Alzheimer’s disease, etc. It was previously demonstrated that high pulsed electrical fields (PEFs) can disrupt the BBB by inducing electroporation (EP) which increases the permeability of the transcellular route. Our goal was to study the effects of low PEFs, well below the threshold of EP on the integrity and function of the BBB. Ten low voltage pulses (5–100 V) were applied to a human in vitro BBB model. Changes in permeability to small molecules (NaF) were studied as well as changes in impedance spectrum and trans-endothelial electric resistivity. Viability and EP were evaluated by Presto-Blue and endogenous Lactate dehydrogenase release assays. The effect on tight junction and adherent junction protein was also studied. The results of low voltage experiments were compared to high voltage experiments (200–1400 V). A significant increase in permeability was found at voltages as low as 10 V despite EP only occurring from 100 V. The changes in permeability as a function of applied voltage were fitted to an inverse-exponential function, suggesting a plateau effect. Staining of VE-cadherin showed specific changes in protein expression. The results indicate that low PEFs can transiently disrupt the BBB by affecting the paracellular route, although the mechanism remains unclear.

Spreading depolarizations trigger caveolin-1-dependent endothelial transcytosis.

Cortical spreading depolarizations (CSDs) are intense and ubiquitous depolarization waves relevant for the pathophysiology of migraine and brain injury. CSDs disrupt the blood-brain barrier (BBB), but the mechanisms are unknown. A total of six CSDs were evoked over 1 hour by topical application of 300 mM of KCl or optogenetically with 470 nm (blue) LED over the right hemisphere in anesthetized mice (C57BL/6 J wild type, Thy1-ChR2-YFP line 18, and cav-1-/- ). BBB disruption was assessed by Evans blue (2% EB, 3 ml/kg, intra-arterial) or dextran (200 mg/kg, fluorescein, 70,000 MW, intra-arterial) extravasation in parietotemporal cortex at 3 to 24 hours after CSD. Endothelial cell ultrastructure was examined using transmission electron microscopy 0 to 24 hours after the same CSD protocol in order to assess vesicular trafficking, endothelial tight junctions, and pericyte integrity. Mice were treated with vehicle, isoform nonselective rho-associated kinase (ROCK) inhibitor fasudil (10 mg/kg, intraperitoneally 30 minutes before CSD), or ROCK-2 selective inhibitor KD025 (200 mg/kg, per oral twice-daily for 5 doses before CSD). We show that CSD-induced BBB opening to water and large molecules is mediated by increased endothelial transcytosis starting between 3 and 6 hours and lasting approximately 24 hours. Endothelial tight junctions, pericytes, and basement membrane remain preserved after CSDs. Moreover, we show that CSD-induced BBB disruption is exclusively caveolin-1-dependent and requires rho-kinase 2 activity. Importantly, hyperoxia failed to prevent CSD-induced BBB breakdown, suggesting that the latter is independent of tissue hypoxia. Our data elucidate the mechanisms by which CSDs lead to transient BBB disruption, with diagnostic and therapeutic implications for migraine and brain injury.

Ultrasound and Microbubble-Mediated Blood-Brain Barrier Disruption for Targeted Delivery of Therapeutics to theBrain.

Ultrasound and microbubble-mediated disruption of the Blood-Brain barrier is a noninvasive and targetable technique that permits the investigation of pharmacological interventions in the brain and CNS. This technique provides an alternative to direct injection of agents into the brain parenchyma or chemical disruption of the Blood-Brain barrier. Here, we detail one protocol for inducing transient Blood-Brain barrier disruption in a rodent model using a commercially available microbubble contrast agent (Definity).

Transient Blood-Brain Barrier Disruption Induced by Cerebral Concussion

Received August 6, 2015 Revised November 3, 2015 Accepted November 3, 2015 Address for correspondence: Hyun Young Park, MD, PhD Department of Neurology, Wonkwang University School of Medicine, 895 Muwang-ro, Iksan 54538, Korea Tel: +82-63-859-1410 Fax: +82-63-842-7379 E-mail: hyppark@hanmail.net 63세 여자가 머리를 바닥에 부딪힌 후 피질경유혼합실어증 (transcortical mixed aphasia)과 우측 편마비(Medical Research Council grade IV)가 발생하였다. 수상 직후 의식소실이나 발작

Intracarotid Infusion of Mesenchymal Stem Cells in an Animal Model of Parkinson's Disease, Focusing on Cell Distribution and Neuroprotective and Behavioral Effects.

Mesenchymal stem cells (MSCs) have been proposed as a potential therapeutic tool for Parkinson's disease (PD) and systemic administration of these cells has been tested in preclinical and clinical studies. However, no information on survival and actual capacity of MSCs to reach the brain has been provided. In this study, we evaluated homing of intraarterially infused rat MSCs (rMSCs) in the brain of rats bearing a 6-hydroxydopamine (6-OHDA)-induced lesion of the nigrostriatal tract, to establish whether the toxin-induced damage is sufficient to grant MSC passage across the blood-brain barrier (BBB) or if a transient BBB disruption is necessary. The rMSC distribution in peripheral organs and the effects of cell infusion on neurodegenerative process and motor deficits were also investigated. rMSCs were infused 14 days after 6-OHDA injection. A hyperosmolar solution of mannitol was used to transiently permeabilize the BBB. Behavioral impairment was assessed by adjusting step test and response to apomorphine. Animals were sacrificed 7 and 28 days after cell infusion. Our work shows that appreciable delivery of rMSCs to the brain of 6-OHDA-lesioned animals can be obtained only after mannitol pretreatment. A notable percentage of infused cells accumulated in peripheral organs. Infusion of rMSCs did not modify the progression of 6-OHDA-induced damage or the motor impairment at the stepping test, but induced progressive normalization of the pathological response (contralateral turning) to apomorphine administration. These findings suggest that many aspects should be further investigated before considering any translation of MSC systemic administration into the clinical setting for PD treatment. This study demonstrates that mesenchymal stem cells infused through the carotid artery do not efficiently cross the blood-brain barrier in rats with a Parkinson's disease-like degeneration of nigrostriatal neurons, unless a permeabilizing agent (e.g., mannitol) is used. The infusion did not reduce the neuronal damage and associated motor impairment, but abolished the motor abnormalities these animals typically show when challenged with a dopaminergic agonist. Therefore, although arterially infused mesenchymal stem cells did not show neurorestorative effects in this study's Parkinson's disease model, they appeared to normalize the pathological responsiveness of striatal neurons to dopaminergic stimulation. This capability should be further explored in future studies.

Transient Blood Brain Barrier Disruption Induced by Oleic Acid is Mediated by Nitric Oxide

The blood brain barrier (BBB) maintains cerebral microenvironmental homeostasis. Transient disruption of the BBB after brain fat embolism in clinical cases and animal models has been reported but the precise mechanism underlying this occurrence is unclear. In the present study, we investigated BBB alterations in rats treated oleic acid (OA) delivered intra-arterially. Following OA treatment, transient brain edema, extravasation of Evans blue and Fluorescein isothiocyanate (FITC)-labeled dextran, and loss of laminin in the affected brain area were observed. Activation of matrix metalloproteinase (MMP)-2, -3, and -13 was found in the cerebral vessels 2 h after OA administration. Expression of intercellular adhesion molecule (ICAM)-1 in the vessels and neutrophil infiltration into the brain tissue was also observed. Inducible nitric oxide synthase (iNOS) was expressed in the neutrophils and nitrotyrosine was produced mainly in the vessels. Inhibitor of iNOS activity suppressed the loss of laminin, leakage of FITC-labeled dextran and Evans blue, and activation of MMP-2 and -13. Protein level of aquaporin (AQ)-4 was increased after OA administration but was not affected by treatment with iNOS inhibitor. In conclusion, we suggest that nitric oxide (NO) contributes to OA-induced MMP activation, BBB disruption and the development of transient brain edema.

Combined ultrasound and MR imaging to guide focused ultrasound therapies in the brain

Several emerging therapies with potential for use in the brain, harness effects produced by acoustic cavitation—the interaction between ultrasound and microbubbles either generated during sonication or introduced into the vasculature. Systems developed for transcranial MRI-guided focused ultrasound (MRgFUS) thermal ablation can enable their clinical translation, but methods for real-time monitoring and control are currently lacking. Acoustic emissions produced during sonication can provide information about the location, strength and type of the microbubble oscillations within the ultrasound field, and they can be mapped in real-time using passive imaging approaches. Here, we tested whether such mapping can be achieved transcranially within a clinical brain MRgFUS system. We integrated an ultrasound imaging array into the hemisphere transducer of the MRgFUS device. Passive cavitation maps were obtained during sonications combined with a circulating microbubble agent at 20 targets in the cingulate cortex in three macaques. The maps were compared with MRI-evident tissue effects. The system successfully mapped microbubble activity during both stable and inertial cavitation, which was correlated with MRI-evident transient blood–brain barrier disruption and vascular damage, respectively. The location of this activity was coincident with the resulting tissue changes within the expected resolution limits of the system. While preliminary, these data clearly demonstrate, for the first time, that it is possible to construct maps of stable and inertial cavitation transcranially, in a large animal model, and under clinically relevant conditions. Further, these results suggest that this hybrid ultrasound/MRI approach can provide comprehensive guidance for targeted drug delivery via blood–brain barrier disruption and other emerging ultrasound treatments, facilitating their clinical translation. We anticipate that it will also prove to be an important research tool that will further the development of a broad range of microbubble-enhanced therapies.

Effect of surface charge and magnetic field on iron oxide nanoparticle permeability in a cell culture model of the blood brain barrier (BBB)

Surface charge and applied magnetic fields affect cellular uptake of iron oxide nanoparticles (IONPs). However, their effects on permeability of IONPs across the BBB remain unexplored. The aim of this study was to determine the impact of IONP surface charge on permeability in a cell culture model of the BBB in the presence and absence of a magnetic field. Permeability of positively (AmS‐) and negatively charged (TMSPEDT)‐IONPs was evaluated in confluent bEnd.3 monolayers grown on polycarbonate membrane inserts (3 μm pore). Our results show neither IONPs were not transported across the monolayer even in presence of magnetic field. When tight junctions were disrupted using D‐mannitol, 44% and 28% of TMSPEDT‐IONPs were found across the monolayer in presence and absence of magnetic field, respectively. Under the same conditions, there was only 10% permeability of the AmS‐IONPs detected. In conclusion, negatively charged IONPs have a more favorable permeability profile in brain endothelial cells via paracellular route following osmotic disruption. Use of TMSPEDT‐IONPs during transient disruption of BBB, may improve nanoparticle based drug delivery to the brain. Support provided by Manitoba Medical Services Foundation, Thorlakson Foundation and NSERC.

MRI Study on Reversible and Irreversible Electroporation Induced Blood Brain Barrier Disruption

Electroporation, is known to induce cell membrane permeabilization in the reversible (RE) mode and cell death in the irreversible (IRE) mode. Using an experimental system designed to produce a continuum of IRE followed by RE around a single electrode we used MRI to study the effects of electroporation on the brain. Fifty-four rats were injected with Gd-DOTA and treated with a G25 electrode implanted 5.5 mm deep into the striata. MRI was acquired immediately after treatment, 10 min, 20 min, 30 min, and up to three weeks following the treatment using: T1W, T2W, Gradient echo (GE), serial SPGR (DCE-MRI) with flip angles ranging over 5–25°, and diffusion-weighted MRI (DWMRI). Blood brain barrier (BBB) disruption was depicted as clear enhancement on T1W images. The average signal intensity in the regions of T1-enhancement, representing BBB disruption, increased from 1887±83 (arbitrary units) immediately post treatment to 2246±94 20 min post treatment, then reached a plateau towards the 30 min scan where it reached 2289±87. DWMRI at 30 min showed no significant effects. Early treatment effects and late irreversible damage were clearly depicted on T2W. The enhancing volume on T2W has increased by an average of 2.27±0.27 in the first 24–48 hours post treatment, suggesting an inflammatory tissue response. The permanent tissue damage, depicted as an enhancing region on T2W, 3 weeks post treatment, decreased to an average of 50±10% of the T2W enhancing volumes on the day of the treatment which was 33±5% of the BBB disruption volume. Permanent tissue damage was significantly smaller than the volume of BBB disruption, suggesting, that BBB disruption is associated with RE while tissue damage with IRE. These results demonstrate the feasibility of applying reversible and irreversible electroporation for transient BBB disruption or permanent damage, respectively, and applying MRI for planning/monitoring disruption volume/shape by optimizing electrode positions and treatment parameters.

On ultrasound-induced microbubble oscillation in a capillary blood vessel and its implications for the blood–brain barrier

The complex interaction between an ultrasound-driven microbubble and an enclosing capillary microvessel is investigated by means of a coupled, multi-domain numerical model using the finite volume formulation. This system is of interest in the study of transient blood–brain barrier disruption (BBBD) for drug delivery applications. The compliant vessel structure is incorporated explicitly as a distinct domain described by a dedicated physical model. Red blood cells (RBCs) are taken into account as elastic solids in the blood plasma. We report the temporal and spatial development of transmural pressure (Ptm) and wall shear stress (WSS) at the luminal endothelial interface, both of which are candidates for the yet unknown mediator of BBBD. The explicit introduction of RBCs shapes the Ptm and WSS distributions and their derivatives markedly. While the peak values of these mechanical wall parameters are not affected considerably by the presence of RBCs, a pronounced increase in their spatial gradients is observed compared to a configuration with blood plasma alone. The novelty of our work lies in the explicit treatment of the vessel wall, and in the modelling of blood as a composite fluid, which we show to be relevant for the mechanical processes at the endothelium.

Ultrasound Enhanced Delivery of Molecular Imaging and Therapeutic Agents in Alzheimer's Disease Mouse Models

Alzheimer's disease is a neurodegenerative disorder typified by the accumulation of a small protein, beta-amyloid, which aggregates and is the primary component of amyloid plaques. Many new therapeutic and diagnostic agents for reducing amyloid plaques have limited efficacy in vivo because of poor transport across the blood-brain barrier. Here we demonstrate that low-intensity focused ultrasound with a microbubble contrast agent may be used to transiently disrupt the blood-brain barrier, allowing non-invasive, localized delivery of imaging fluorophores and immunotherapeutics directly to amyloid plaques. We administered intravenous Trypan blue, an amyloid staining red fluorophore, and anti-amyloid antibodies, concurrently with focused ultrasound therapy in plaque-bearing, transgenic mouse models of Alzheimer's disease with amyloid pathology. MRI guidance permitted selective treatment and monitoring of plaque-heavy anatomical regions, such as the hippocampus. Treated brain regions exhibited 16.5±5.4-fold increase in Trypan blue fluorescence and 2.7±1.2-fold increase in anti-amyloid antibodies that localized to amyloid plaques. Ultrasound-enhanced delivery was consistently reproduced in two different transgenic strains (APPswe:PSEN1dE9, PDAPP), across a large age range (9–26 months), with and without MR guidance, and with little or no tissue damage. Ultrasound-mediated, transient blood-brain barrier disruption allows the delivery of both therapeutic and molecular imaging agents in Alzheimer's mouse models, which should aid pre-clinical drug screening and imaging probe development. Furthermore, this technique may be used to deliver a wide variety of small and large molecules to the brain for imaging and therapy in other neurodegenerative diseases.