Transient Blood-brain Barrier Opening Research Articles

In vivo imaging of sterile microglial activation in rat brain after disrupting the blood-brain barrier with pulsed focused ultrasound: [18F]DPA-714 PET study

BackgroundMagnetic resonance imaging (MRI)-guided pulsed focused ultrasound combined with the infusion of microbubbles (pFUS+MB) induces transient blood-brain barrier opening (BBBO) in targeted regions. pFUS+MB, through the facilitation of neurotherapeutics’ delivery, has been advocated as an adjuvant treatment for neurodegenerative diseases and malignancies. Sterile neuroinflammation has been recently described following pFUS+MB BBBO. In this study, we used PET imaging with [18F]-DPA714, a biomarker of translocator protein (TSPO), to assess for neuroinflammatory changes following single and multiple pFUS+MB sessions.MethodsThree groups of Sprague-Dawley female rats received MRI-guided pFUS+MB (Optison™; 5–8 × 107 MB/rat) treatments to the left frontal cortex and right hippocampus. Group A rats were sonicated once. Group B rats were sonicated twice and group C rats were sonicated six times on weekly basis. Passive cavitation detection feedback (PCD) controlled the peak negative pressure during sonication. We performed T1-weighted scans immediately after sonication to assess efficiency of BBBO and T2*-weighted scans to evaluate for hypointense voxels. [18F]DPA-714 PET/CT scans were acquired after the BBB had closed, 24 h after sonication in group A and within an average of 10 days from the last sonication in groups B and C. Ratios of T1 enhancement, T2* values, and [18F]DPA-714 percent injected dose/cc (%ID/cc) values in the targeted areas to the contralateral brain were calculated. Histological assessment for microglial activation/astrocytosis was performed.ResultsIn all groups, [18F]DPA-714 binding was increased at the sonicated compared to non-sonicated brain (%ID/cc ratios > 1). Immunohistopathology showed increased staining for microglial and astrocytic markers in the sonicated frontal cortex compared to contralateral brain and to a lesser extent in the sonicated hippocampus. Using MRI, we documented BBB disruption immediately after sonication with resolution of BBBO 24 h later. We found more T2* hypointense voxels with increasing number of sonications. In a longitudinal group of animals imaged after two and after six sonications, there was no cumulative increase of neuroinflammation on PET.ConclusionUsing [18F]DPA-714 PET, we documented in vivo neuroinflammatory changes in association with pFUS+MB. Our protocol (utilizing PCD feedback to minimize damage) resulted in neuroinflammation visualized 24 h post one sonication. Our findings were supported by immunohistochemistry showing microglial activation and astrocytosis. Experimental sonication parameters intended for BBB disruption should be evaluated for neuroinflammatory sequelae prior to implementation in clinical trials.

Moving toward Noninvasive, Focused Ultrasound Therapeutic Delivery of Drugs in the Brain: Prolonged Opening of Blood-Brain Barrier May Not Be Needed.

Moving toward Noninvasive, Focused Ultrasound Therapeutic Delivery of Drugs in the Brain: Prolonged Opening of Blood-Brain Barrier May Not Be Needed.

Blood-Brain Barrier Opening in Primary Brain Tumors with Non-invasive MR-Guided Focused Ultrasound: A Clinical Safety and Feasibility Study

The blood-brain barrier (BBB) has long limited therapeutic access to brain tumor and peritumoral tissue. In animals, MR-guided focused ultrasound (MRgFUS) with intravenously injected microbubbles can temporarily and repeatedly disrupt the BBB in a targeted fashion, without open surgery. Our objective is to demonstrate safety and feasibility of MRgFUS BBB opening with systemically administered chemotherapy in patients with glioma in a phase I, single-arm, open-label study. Five patients with previously confirmed or suspected high-grade glioma based on imaging underwent the MRgFUS in conjunction with administration of chemotherapy (n = 1 liposomal doxorubicin, n = 4 temozolomide) one day prior to their scheduled surgical resection. Samples of “sonicated” and “unsonicated” tissue were measured for the chemotherapy by liquid-chromatography-mass spectrometry. Complete follow-up was three months. The procedure was well-tolerated, with no adverse clinical or radiologic events related to the procedure. The BBB within the target volume showed radiographic evidence of opening with an immediate 15–50% increased contrast enhancement on T1-weighted MRI, and resolution approximately 20 hours after. Biochemical analysis of sonicated versus unsonicated tissue suggest chemotherapy delivery is feasible. In this study, we demonstrated transient BBB opening in tumor and peritumor tissue using non-invasive low-intensity MRgFUS with systemically administered chemotherapy was safe and feasible. The characterization of therapeutic delivery and clinical response to this treatment paradigm requires further investigation.

Mechanisms of enhanced antiglioma efficacy of polysorbate 80-modified paclitaxel-loaded PLGA nanoparticles by focused ultrasound.

The presence of blood‐brain barrier (BBB) greatly limits the availability of drugs and their efficacy against glioma. Focused ultrasound (FUS) can induce transient and local BBB opening for enhanced drug delivery. Here, we developed polysorbate 80‐modified paclitaxel‐loaded PLGA nanoparticles (PS‐80‐PTX‐NPs, PPNP) and examined the enhanced local delivery into the brain for glioma treatment by combining with FUS. Our result showed PPNP had good stability, fast drug release rate and significant toxicity to glioma cells. Combined with FUS, PPNP showed a stronger BBB permeation efficiency both in the in vitro and in vivo BBB models. Mechanism studies revealed the disrupted tight junction, reduced P‐glycoprotein expression and ApoE‐dependent PS‐80 permeation collectively contribute to the enhanced drug delivery, resulting in significantly stronger antitumour efficacy and longer survival time in the tumour‐bearing mice. Our study provided a new strategy to efficiently and locally deliver drugs into the brain to treat glioma.

Reversible opening of the blood-brain barrier by claudin-5-binding variants of Clostridium perfringens enterotoxin's claudin-binding domain

The blood-brain barrier (BBB) prevents entry of neurotoxic substances but also that of drugs into the brain. Here, the paracellular barrier is formed by tight junctions (TJs) with claudin-5 (Cldn5) being the main sealing constituent. Transient BBB opening by targeting Cldn5 could improve paracellular drug delivery. The non-toxic C-terminal domain of Clostridium perfringens enterotoxin (cCPE) binds to a subset of claudins, e.g., Cldn3, -4. Structure-based mutagenesis was used to generate Cldn5-binding variants (cCPE-Y306W/S313H and cCPE-N218Q/Y306W/S313H). These cCPE-variants were tested for transient TJ opening using multiple in vitro BBB models: Primary porcine brain endothelial cells, coculture of primary rat brain endothelial cells with astrocytes and mouse cerebEND cells. cCPE-Y306W/S313H and cCPE-N218Q/Y306W/S313H but neither cCPE-wt nor cCPE-Y306A/L315A (not binding to claudins) decreased transendothelial electrical resistance in a concentration-dependent and reversible manner. Furthermore, permeability of carboxyfluorescein (with size of CNS drugs) was increased. cCPE-Y306W/S313H but neither cCPE-wt nor cCPE-Y306A/L315A bound to Cldn5-expressing brain endothelial cells. However, freeze-fracture EM showed that cCPE-Y306W/S313H did not cause drastic TJ breakdown. In sum, Cldn5-binding cCPE-variants enabled mild and transient opening of brain endothelial TJs. Using reliable in vitro BBB models, the results demonstrate that cCPE-based biologics designed to bind Cldn5 improve paracellular drug delivery across the BBB.

Establishing sheep as an experimental species to validate ultrasound-mediated blood-brain barrier opening for potential therapeutic interventions

Rationale: Treating diseases of the brain such as Alzheimer's disease (AD) is challenging as the blood-brain barrier (BBB) effectively restricts access of a large number of potentially useful drugs. A potential solution to this problem is presented by therapeutic ultrasound, a novel treatment modality that can achieve transient BBB opening in species including rodents, facilitated by biologically inert microbubbles that are routinely used in a clinical setting for contrast enhancement. However, in translating rodent studies to the human brain, the presence of a thick cancellous skull that both absorbs and distorts ultrasound presents a challenge. A larger animal model that is more similar to humans is therefore required in order to establish a suitable protocol and to test devices. Here we investigated whether sheep provide such a model.Methods: In a stepwise manner, we used a total of 12 sheep to establish a sonication protocol using a spherically focused transducer. This was assisted by ex vivo simulations based on CT scans to establish suitable sonication parameters. BBB opening was assessed by Evans blue staining and a range of histological tests.Results: Here we demonstrate noninvasive microbubble-mediated BBB opening through the intact sheep skull. Our non-recovery protocol allowed for BBB opening at the base of the brain, and in areas relevant for AD, including the cortex and hippocampus. Linear time-shift invariant analysis and finite element analysis simulations were used to optimize the position of the transducer and to predict the acoustic pressure and location of the focus.Conclusion: Our study establishes sheep as a novel animal model for ultrasound-mediated BBB opening and highlights opportunities and challenges in using this model. Moreover, as sheep develop an AD-like pathology with aging, they represent a large animal model that could potentially complement the use of non-human primates.

Size-selective opening of the blood–brain barrier by targeting endothelial sphingosine 1–phosphate receptor 1

The vasculature of the central nervous system (CNS) forms a selective barrier termed the blood-brain barrier (BBB). Disruption of the BBB may contribute to various CNS diseases. Conversely, the intact BBB restricts efficient penetration of CNS-targeted drugs. Here, we report the BBB-regulatory role of endothelial sphingosine 1-phosphate (S1P) receptor-1, a G protein-coupled receptor known to promote the barrier function in peripheral vessels. Endothelial-specific S1pr1 knockout mice (S1pr1iECKO ) showed BBB breach for small-molecular-mass fluorescence tracers (<3 kDa), but not larger tracers (>10 kDa). Chronic BBB leakiness was associated with cognitive impairment, as assessed by the novel object recognition test, but not signs of brain inflammation. Brain microvessels of S1pr1iECKO mice showed altered subcellular distribution of tight junctional proteins. Pharmacological inhibition of S1P1 function led to transient BBB breach. These data suggest that brain endothelial S1P1 maintain the BBB by regulating the proper localization of tight junction proteins and raise the possibility that endothelial S1P1 inhibition may be a strategy for transient BBB opening and delivery of small molecules into the CNS.

Pharmacokinetic analysis and drug delivery efficiency of the focused ultrasound-induced blood-brain barrier opening in non-human primates

PurposeFocused Ultrasound (FUS) in conjunction with systemically administered microbubbles has been shown to open the Blood-Brain Barrier (BBB) locally, non-invasively and reversibly in rodents and non-human primates (NHP), suggesting the immense potential of this technique. The objective of this study entailed the investigation of the physiologic changes in the brain following the FUS-induced BBB opening and their relationship with the underlying anatomy. Materials and methodsPharmacokinetic analysis was implemented in NHP's that received FUS at various acoustic pressures. Relaxivity mapping enabled the robust quantitative detection of the BBB opening as well as grey and white matter segmentation. Drug delivery efficiency was measured for pre-clinical validation of the technique. ResultsBased on our results, the opening volume and the amount of the gadolinium delivered were found mostly contained in the grey matter, while FUS-induced permeability and drug concentration varied depending upon the underlying brain inhomogeneity, and increased with the acoustic pressure. ConclusionsOverall, apart from the in vivo protocols for BBB analysis developed here, this study also suggests the important role that FUS can have in efficient drug delivery via localized and transient BBB opening.

Glutamate-Mediated Blood-Brain Barrier Opening: Implications for Neuroprotection and Drug Delivery

The blood-brain barrier is a highly selective anatomical and functional interface allowing a unique environment for neuro-glia networks. Blood-brain barrier dysfunction is common in most brain disorders and is associated with disease course and delayed complications. However, the mechanisms underlying blood-brain barrier opening are poorly understood. Here we demonstrate the role of the neurotransmitter glutamate in modulating early barrier permeability in vivo Using intravital microscopy, we show that recurrent seizures and the associated excessive glutamate release lead to increased vascular permeability in the rat cerebral cortex, through activation of NMDA receptors. NMDA receptor antagonists reduce barrier permeability in the peri-ischemic brain, whereas neuronal activation using high-intensity magnetic stimulation increases barrier permeability and facilitates drug delivery. Finally, we conducted a double-blind clinical trial in patients with malignant glial tumors, using contrast-enhanced magnetic resonance imaging to quantitatively assess blood-brain barrier permeability. We demonstrate the safety of stimulation that efficiently increased blood-brain barrier permeability in 10 of 15 patients with malignant glial tumors. We suggest a novel mechanism for the bidirectional modulation of brain vascular permeability toward increased drug delivery and prevention of delayed complications in brain disorders. In this study, we reveal a new mechanism that governs blood-brain barrier (BBB) function in the rat cerebral cortex, and, by using the discovered mechanism, we demonstrate bidirectional control over brain endothelial permeability. Obviously, the clinical potential of manipulating BBB permeability for neuroprotection and drug delivery is immense, as we show in preclinical and proof-of-concept clinical studies. This study addresses an unmet need to induce transient BBB opening for drug delivery in patients with malignant brain tumors and effectively facilitate BBB closure in neurological disorders.

Reduced graphene oxide induces transient blood-brain barrier opening: an in vivo study.

BackgroundThe blood–brain barrier (BBB) is a complex physical and functional barrier protecting the central nervous system from physical and chemical insults. Nevertheless, it also constitutes a barrier against therapeutics for treating neurological disorders. In this context, nanomaterial-based therapy provides a potential alternative for overcoming this problem. Graphene family has attracted significant interest in nanomedicine because their unique physicochemical properties make them amenable to applications in drug/gene delivery and neural interface.ResultsIn this study, reduced graphene oxide (rGO) systemically-injected was found mainly located in the thalamus and hippocampus of rats. The entry of rGO involved a transitory decrease in the BBB paracellular tightness, as demonstrated at anatomical (Evans blue dye infusion), subcellular (transmission electron microscopy) and molecular (junctional protein expression) levels. Additionally, we examined the usefulness of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) as a new imaging method for detecting the temporal distribution of nanomaterials throughout the brain.ConclusionsrGO was able to be detected and monitored in the brain over time provided by a novel application for MALDI-MSI and could be a useful tool for treating a variety of brain disorders that are normally unresponsive to conventional treatment because of BBB impermeability.

Feasibility and Safety of Intra-arterial Pericyte Progenitor Cell Delivery Following Mannitol-Induced Transient Blood-Brain Barrier Opening in a Canine Model.

Stem cell therapy is currently being studied with a view to rescuing various neurological diseases. Such studies require not only the discovery of potent candidate cells but also the development of methods that allow optimal delivery of those candidates to the brain tissues. Given that the blood-brain barrier (BBB) precludes cells from entering the brain, the present study was designed to test whether hyperosmolar mannitol securely opens the BBB and enhances intra-arterial cell delivery. A noninjured normal canine model in which the BBB was presumed to be closed was used to evaluate the feasibility and safety of the tested protocol. Autologous adipose tissue-derived pericytes with platelet-derived growth factor receptor β positivity were utilized. Cells were administered 5 min after mannitol pretreatment using one of following techniques: (1) bolus injection of a concentrated suspension, (2) continuous infusion of a diluted suspension, or (3) bolus injection of a concentrated suspension that had been shaken by repeated syringe pumping. Animals administered a concentrated cell suspension without mannitol pretreatment served as a control group. Vital signs, blood parameters, neurologic status, and major artery patency were kept stable throughout the experiment and the 1-month posttreatment period. Although ischemic lesions were noted on magnetic resonance imaging in several mongrel dogs with concentrated cell suspension, the injection technique using repeated syringe shaking could avert this complication. The cells were detected in both ipsilateral and contralateral cortices and were more frequent at the ipsilateral and frontal locations, whereas very few cells were observed anywhere in the brain when mannitol was not preinjected. These data suggest that intra-arterial cell infusion with mannitol pretreatment is a feasible and safe therapeutic approach in stable brain diseases such as chronic stroke.

Blood-brain barrier opening-based local delivery of 80 nm-sized liposomes in mice using pulsed focused ultrasound

Continuous focused ultrasound (FUS) has been mostly used to generate high temperatures necessary for tissue ablation. Pulsed FUS in combination with intravenously injected microbubbles has been shown to open the blood-brain barrier (BBB) to increase plasma-to-tissue permeability, thus presenting a new opportunity for local drug delivery to the targeted part of the brain. We have previously demonstrated a local delivery of doxorubicin to mouse brain tumor tissues by transient BBB opening.[1] However, the next generation of therapeutics is associated with a broader range of clinically meaningful applications. Liposomes are particularly interesting since drug and contrast agent can be combined in a single safe and biodegradable system with a sustained release of content. Therefore, we investigated the brain delivery of fluorescently labeled liposomes by FUS-mediated BBB opening in healthy mice.

Submicron-bubble-enhanced focused ultrasound for blood-brain barrier disruption and improved CNS drug delivery.

The use of focused ultrasound (FUS) with microbubbles has been proven to induce transient blood–brain barrier opening (BBB-opening). However, FUS-induced inertial cavitation of microbubbles can also result in erythrocyte extravasations. Here we investigated whether induction of submicron bubbles to oscillate at their resonant frequency would reduce inertial cavitation during BBB-opening and thereby eliminate erythrocyte extravasations in a rat brain model. FUS was delivered with acoustic pressures of 0.1–4.5 MPa using either in-house manufactured submicron bubbles or standard SonoVue microbubbles. Wideband and subharmonic emissions from bubbles were used to quantify inertial and stable cavitation, respectively. Erythrocyte extravasations were evaluated by in vivo post-treatment magnetic resonance susceptibility-weighted imaging, and finally by histological confirmation. We found that excitation of submicron bubbles with resonant frequency-matched FUS (10 MHz) can greatly limit inertial cavitation while enhancing stable cavitation. The BBB-opening was mainly caused by stable cavitation, whereas the erythrocyte extravasation was closely correlated with inertial cavitation. Our technique allows extensive reduction of inertial cavitation to induce safe BBB-opening. Furthermore, the safety issue of BBB-opening was not compromised by prolonging FUS exposure time, and the local drug concentrations in the brain tissues were significantly improved to 60 times (BCNU; 18.6 µg versus 0.3 µg) by using chemotherapeutic agent-loaded submicron bubbles with FUS. This study provides important information towards the goal of successfully translating FUS brain drug delivery into clinical use.

Platelet activating factor induces transient blood‐brain barrier opening to facilitate edaravone penetration into the brain

The blood-brain barrier (BBB) greatly limits the efficacy of many neuroprotective drugs' delivery to the brain, so improving drug penetration through the BBB has been an important focus of research. Here we report that platelet activating factor (PAF) transiently opened BBB and facilitated neuroprotectant edaravone penetration into the brain. Intravenous infusion with PAF induced a transient BBB opening in rats, reflected by increased Evans blue leakage and mild edema formation, which ceased within 6 h. Furthermore, rat regional cerebral blood flow (rCBF) declined acutely during PAF infusion, but recovered slowly. More importantly, this transient BBB opening significantly increased the penetration of edaravone into the brain, evidenced by increased edaravone concentrations in tissue interstitial fluid collected by microdialysis and analyzed by Ultra-performance liquid chromatograph combined with a hybrid quadrupole time-of-flight mass spectrometer (UPLC-MS/MS). Similarly, incubation of rat brain microvessel endothelial cells monolayer with 1 μM PAF for 1 h significantly increased monolayer permeability to (125)I-albumin, which recovered 1 h after PAF elimination. However, PAF incubation with rat brain microvessel endothelial cells for 1 h did not cause detectable cytotoxicity, and did not regulate intercellular adhesion molecule-1, matrix-metalloproteinase-9 and P-glycoprotein expression. In conclusion, PAF could induce transient and reversible BBB opening through abrupt rCBF decline, which significantly improved edaravone penetration into the brain. Platelet activating factor (PAF) transiently induces BBB dysfunction and increases BBB permeability, which may be due to vessel contraction and a temporary decline of regional cerebral blood flow (rCBF) triggered by PAF. More importantly, the PAF induced transient BBB opening facilitates neuroprotectant edaravone penetration into brain. The results of this study may provide a new approach to improve drug delivery into the brain.

Focused ultrasound-induced blood–brain barrier disruption enhances the delivery of cytarabine to the rat brain

To investigate the feasibility of using focused ultrasound (FUS) with microbubbles for targeted delivery of cytarabine to the brain. Sprague–Dawly rats (weighing 200–250 g) received focused ultrasound with intravenous injection microbubbles. At 0, 2, 4, 8, and 24 hours (n = 5 for each time point) after sonication, animals received intravenous administration of cytarabine at a normal dose of 4 mg/kg body weight. Additional five rats were given with a high dose (50 mg/kg body weight) of cytarabine alone. Blood–brain barrier (BBB) permeability and cerebral cytarabine were determined. FUS in conjunction with microbubbles caused a transient BBB opening. Sonication exposure promoted cytarabine accumulation at the sonicated site. Animals injected with a normal dose of cytarabine 2 hours after sonication had similar concentrations of cerebral cytarabine compared to those with higher cytarabine without sonication. FUS can temporarily open the BBB and thus facilitate the penetration of systemic cytarabine into the brain.

The Role of Caveolin-1 in Blood–Brain Barrier Disruption Induced by Focused Ultrasound Combined with Microbubbles

This research was designed to determine whether disrupting the blood-brain barrier (BBB) in rats by applying focused ultrasound (FUS) combined with microbubbles induced changes in the density of caveolae and/or the expression of the structural protein caveolin-1. To this end, two approaches were utilized. First, using enhanced magnetic resonance imaging, characteristics of BBB disruption induced by our specific FUS parameters and dose of microbubble were recorded, and the time after treatment when the BBB was the most permeable was determined. Second, rats were treated with FUS or microbubbles alone, both or neither, and a combination of Evans blue (EB) BBB permeability assays, streptavidin-peroxidase (SP) immunohistochemistry, western blot, and transmission electron microscopy (TEM) was employed to detect any changes in caveolae density and caveolin-1 expression at the previously determined time point when the BBB was the most permeable. The first set of studies revealed that our specific FUS parameters and dose of microbubbles were able to induce a transient, targeted, and reversible BBB opening in rats, and that the BBB was the most permeable 1 h after treatment with FUS and microbubbles. In the second set of experiments, the results of the SP immunohistochemistry, western blot, and TEM, taken together, revealed that caveolae and caveolin-1 were primarily localized in the brain microvascular endothelial cells of all of the rats regardless of treatment, and that caveolin-1 expression was highest in the rats treated with both FUS and microbubbles. In summary, treatment with FUS, in combination with a dose of microbubbles, can enhance BBB permeability through a caveolae-mediated transcellular approach by upregulating the expression level of caveolin-1 and, consequently, the amount of caveolae. This caveolin-1-mediated transcellular transport pathway may cooperate with other transport pathways to induce opening of the BBB. This research sheds light on the mechanism of a transient, targeted, and reversible opening of the BBB induced by FUS combined with microbubbles.

Alterations of Fc gamma receptor I and Toll‐like receptor 4 mediate the antiinflammatory actions of microglia and astrocytes after adrenaline‐induced blood–brain barrier opening in rats

Blood-brain barrier (BBB) opening occurs under many physiological and pathological conditions. BBB opening will lead to the leakage of large circulating molecules into the brain parenchyma. These invasive molecules will induce immune responses. Microglia and astrocytes are the two major cell types responsible for immune responses in the brain, and Fc gamma receptor I (FcgammaRI) and Toll-like receptor 4 (TLR4) are the two important receptors mediating these processes. Data suggest that activation of the FcgammaRI pathway mediates antiinflammatory processes, whereas activation of TLR4 pathway leads to proinflammatory activities. In the present study, we tested the hypothesis that BBB opening could lead to alterations in FcgammaRI and TLR4 pathways in microglia and astrocytes, thus limiting excessive inflammation in the brain. The transient BBB opening was induced by adrenaline injection through a caudal vein in Sprague-Dawley rats. We found that the FcgammaRI pathway was significantly activated in both microglia and astrocytes, as exhibited by the up-regulation of FcgammaRI and its key downstream molecule Syk, as well as the increased production of the effector cytokines, interleukin (IL)-10 and IL-4. Interestingly, after transient BBB opening, TLR4 expression was also increased. However, the expression of MyD88, the central adapter of the TLR4 pathway, was significantly inhibited, with decreased production of the effector cytokines IL-12a and IL-1beta. These results indicate that, after transient BBB opening, FcgammaRI-mediated antiinflammatory processes were activated, whereas TLR4-mediated proinflammatory activities were inhibited in microglia and astrocytes. This may represent an important neuroprotective mechanism of microglia and astrocytes that limits excessive inflammation after BBB opening.

Noninvasive and Transient Blood-Brain Barrier Opening in the Hippocampus of Alzheimer's Double Transgenic Mice Using Focused Ultrasound

The spatio-temporal nature of focused ultrasound-induced blood-brain barrier (BBB) opening as a brain drug delivery method was investigated in Alzheimer's disease model mice. The left hippocampus of transgenic (APP/PS1, n = 3) and nontransgenic (n = 3) mice was sonicated (frequency: 1.525 MHz, peak-negative pressure: 600 kPa, pulse length: 20 ms, duty cycle: 20%, duration: 1 min) in vivo, through their intact skin and skull, after intravenous injection of microbubbles (SonoVue; 25 microl). Sequential, high-field MR images (9.4 Tesla) were acquired before and after injection of gadolinium (Omniscan, 0.75 ml, molecular weight: 573.7 Da) on two separate days for each mouse. Gadolinium deposits through the ultrasound-induced BBB opening in the left hippocampus revealed significant contrast-enhancement in the MRI. On the following day, MRI revealed significant BBB closure within the same region. However, the BBB opening extent and BBB closing timeline varied in different regions within the same sonicated location. This indicates that opening and closing were dependent on the brain region targeted. No significant difference in BBB opening or closing behaviors was observed between the APP/PS1 and the nontransgenic mice. In conclusion, a BBB-impermeable molecule was noninvasively, transiently and reproducibly delivered to the hippocampus of Alzheimer's APP/PS1 mice.

Acute blood-brain barrier changes in experimental closed head injury as measured by MRI and Gd-DTPA.

The objective of this study was to determine the early time course of blood-brain barrier (BBB) changes in diffuse closed head injury (CHI) and to what extent BBB is affected by secondary insult. The BBB disruption was quantified using T1-weighted MRI following administration of Gd-DTPA. The maximal signal intensity (SI) enhancement was used to calculate BBB disruption. A new CHI model was used to induce injury. Adult SD rats were separated into four groups: Group I: Sham (n = 4), II: Hypoxia and Hypotension (HH, n = 4), III: Trauma alone (n = 23), and IV: Trauma coupled with HH (THH, n = 14). Following trauma, a 30 minute insult of hypoxia (PaO2 = 40 mmHg) and hypotension (MABP = 30 mmHg) were imposed. In trauma animals, SI increased dramatically immediately following impact. By 15 minutes, permeability decreased exponentially and by 30 minutes was equal to that of control. In THH animals, SI enhancement was lower after the trauma, consistent with reduced blood pressure and blood flow. However, the SI increased dramatically upon reperfusion and was equal to that of control after 60 minutes. In conclusion we may consider, that CHI is associated with a rapid and transient BBB opening which begins at the time of the trauma and lasts not more than 30 minutes. It has been also shown that addition of hypoxia and hypotension prolongs the time of BBB breakdown.

Magnetic resonance imaging-monitored acute blood-brain barrier changes in experimental traumatic brain injury.

The authors posit that cellular edema is the major contributor to brain swelling in diffuse head injury and that the contribution of vasogenic edema may be overemphasized. The objective of this study was to determine the early time course of blood-brain barrier (BBB) changes in diffuse closed head injury and to what extent barrier permeability is affected by the secondary insults of hypoxia and hypotension. The BBB disruption was quantified and visualized using T1-weighted magnetic resonance (MR) imaging following intravenous administration of the MR contrast agent gadolinium-diethylenetriamine pentaacetic acid. To avoid the effect of blood volume changes, the maximum signal intensity (SI) enhancement was used to calculate the difference in BBB disruption. A new impact-acceleration model was used to induce closed head injury. Forty-five adult Sprague-Dawley rats were separated into four groups: Group I, sham operated (four animals), Group II, hypoxia and hypotension (four animals), Group III, trauma only (23 animals), and Group IV, trauma coupled with hypoxia and hypotension (14 animals). After trauma was induced, a 30-minute insult of hypoxia (PaO2 40 mm Hg) and hypotension (mean arterial blood pressure 30 mm Hg) was imposed, after which the animals were resuscitated. In the trauma-induced animals, the SI increased dramatically immediately after impact. By 15 minutes permeability decreased exponentially and by 30 minutes it was equal to that of control animals. When trauma was coupled with secondary insult, the SI enhancement was lower after the trauma, consistent with reduced blood pressure and blood flow. However, the SI increased dramatically on reperfusion and was equal to that of control by 60 minutes after the combined insult. In conclusion, the authors suggest that closed head injury is associated with a rapid and transient BBB opening that begins at the time of the trauma and lasts no more than 30 minutes. It has also been shown that addition of posttraumatic secondary insult-hypoxia and hypotension-prolongs the time of BBB breakdown after closed head injury. The authors further conclude that MR imaging is an excellent technique to follow (time resolution 1-1.5 minutes) the evolution of trauma-induced BBB damage noninvasively from as early as a few minutes up to hours or even longer after the trauma occurs.