The application of MRI for depiction of subtle blood brain barrier disruption in stroke

Transcranial blood-brain barrier opening in Alzheimer's disease patients using a portable focused ultrasound system with real-time 2-D cavitation mapping

Background : Focused ultrasound (FUS) in combination with microbubbles has recently shown great promise in facilitating blood-brain barrier (BBB) opening for drug delivery and immunotherapy in Alzheimer's disease (AD). However, it is currently limited to systems integrated within the MRI suites or requiring post-surgical implants, thus restricting its widespread clinical adoption. In this pilot study, we investigate the clinical safety and feasibility of a portable, non-invasive neuronavigation-guided FUS (NgFUS) system with integrated real-time 2-D microbubble cavitation mapping. Methods : A phase 1 clinical study with mild to moderate AD patients (N = 6) underwent a single session of microbubble-mediated NgFUS to induce transient BBB opening (BBBO). Microbubble activity under FUS was monitored with real-time 2-D cavitation maps and dosing to ensure the efficacy and safety of the NgFUS treatment. Post-operative MRI was used for BBB opening and closure confirmation as well as safety assessment. Changes in AD biomarker levels in both blood serum and extracellular vesicles (EVs) were evaluated, while changes in amyloid-beta (Aβ) load in the brain were assessed through 18F-florbetapir PET. Results : BBBO was achieved in 5 out of 6 subjects with an average volume of 983 ± 626 mm3 following FUS at the right frontal lobe both in white and gray matter regions. The outpatient treatment was completed within 34.8 ± 10.7 min. Cavitation dose significantly correlated with the BBBO volume (R 2 > 0.9, N = 4), demonstrating the portable NgFUS system's capability of predicting opening volumes. The cavitation maps co-localized closely with the BBBO location, representing the first report of real-time transcranial 2-D cavitation mapping in the human brain. Larger opening volumes correlated with increased levels of AD biomarkers, including Aβ42 (R 2 = 0.74), Tau (R 2 = 0.95), and P-Tau181 (R 2 = 0.86), assayed in serum-derived EVs sampled 3 days after FUS (N = 5). From PET scans, subjects showed a lower Aβ load increase in the treated frontal lobe region compared to the contralateral region. Reduction in asymmetry standardized uptake value ratios (SUVR) correlated with the cavitation dose (R 2 > 0.9, N = 3). Clinical changes in the mini-mental state examination over 6 months were within the expected range of cognitive decline with no additional changes observed as a result of FUS. Conclusion : We showed the safety and feasibility of this cost-effective and time-efficient portable NgFUS treatment for BBBO in AD patients with the first demonstration of real-time 2-D cavitation mapping. The cavitation dose correlated with BBBO volume, a slowed increase in pathology, and serum detection of AD proteins. Our study highlights the potential for accessible FUS treatment in AD, with or without drug delivery.

Transcranial Blood-Brain Barrier Opening in Alzheimer's Disease Patients Using a Portable Focused Ultrasound System with Real-Time 2-D Cavitation Mapping

Background

Focused ultrasound (FUS) in combination with microbubbles has recently shown great promise in facilitating blood-brain barrier (BBB) opening for drug delivery and immunotherapy in Alzheimer's disease (AD). However, it is currently limited to systems integrated within the MRI suites or requiring post-surgical implants, thus restricting its widespread clinical adoption. In this pilot study, we investigate the clinical safety and feasibility of a portable, non-invasive neuronavigation-guided FUS (NgFUS) system with integrated real-time 2-D microbubble cavitation mapping.

Methods

A phase 1 clinical study with mild to moderate AD patients (N=6) underwent a single session of microbubble-mediated NgFUS to induce transient BBB opening (BBBO). Microbubble activity under FUS was monitored with real-time 2-D cavitation maps and dosing to ensure the efficacy and safety of the NgFUS treatment. Post-operative MRI was used for BBB opening and closure confirmation as well as safety assessment. Changes in AD biomarker levels in both blood serum and extracellular vesicles (EVs) were evaluated, while changes in amyloid-beta (Aβ) load in the brain were assessed through 18F-Florbetapir PET.

Results

BBBO was achieved in 5 out of 6 subjects with an average volume of 983±626 mm3 following FUS at the right frontal lobe both in white and gray matter regions. The outpatient treatment was completed within 34.8±10.7 min. Cavitation dose significantly correlated with the BBBO volume (R 2>0.9, N=4), demonstrating the portable NgFUS system's capability of predicting opening volumes. The cavitation maps co-localized closely with the BBBO location, representing the first report of real-time transcranial 2-D cavitation mapping in the human brain. Larger opening volumes correlated with increased levels of AD biomarkers, including Aβ42 (R 2=0.74), Tau (R 2=0.95), and P-Tau181 (R 2=0.86), assayed in serum-derived EVs sampled 3 days after FUS (N=5). From PET scans, subjects showed a lower Aβ load increase in the treated frontal lobe region compared to the contralateral region. Reduction in asymmetry standardized uptake value ratios (SUVR) correlated with the cavitation dose (R 2>0.9, N=3). Clinical changes in the mini-mental state examination over 6 months were within the expected range of cognitive decline with no additional changes observed as a result of FUS.

Conclusion

We showed the safety and feasibility of this cost-effective and time-efficient portable NgFUS treatment for BBBO in AD patients with the first demonstration of real-time 2-D cavitation mapping. The cavitation dose correlated with BBBO volume, a slowed increase in pathology, and serum detection of AD proteins. Our study highlights the potential for accessible FUS treatment in AD, with or without drug delivery.

Late/delayed gadolinium enhancement in MRI after intravenous administration of extracellular gadolinium-based contrast agents: is it worth waiting?

The acquisition of images minutes or even hours after intravenous extracellular gadolinium-based contrast agents (GBCA) administration ("Late/Delayed Gadolinium Enhancement" imaging; in this review, further termed LGE) has gained significant prominence in recent years in magnetic resonance imaging. The major limitation of LGE is the long examination time; thus, it becomes necessary to understand when it is worth waiting time after the intravenous injection of GBCA and which additional information comes from LGE. LGE can potentially be applied to various anatomical sites, such as heart, arterial vessels, lung, brain, abdomen, breast, and the musculoskeletal system, with different pathophysiological mechanisms. One of the most popular clinical applications of LGE regards the assessment of myocardial tissue thanks to its ability to highlight areas of acute myocardial damage and fibrotic tissues. Other frequently applied clinical contexts involve the study of the urinary tract with magnetic resonance urography and identifying pathological abdominal processes characterized by high fibrous stroma, such as biliary tract tumors, autoimmune pancreatitis, or intestinal fibrosis in Crohn's disease. One of the current areas of heightened research interest revolves around the possibility of non-invasively studying the dynamics of neurofluids in the brain (the glymphatic system), the disruption of which could underlie many neurological disorders.

Telmisartan as an add-on treatment for dogs with refractory idiopathic epilepsy: a nonrandomized, uncontrolled, open-label clinical trial

OBJECTIVE

To evaluate the effect on seizure frequency of add-on telmisartan treatment in dogs with refractory idiopathic epilepsy.

ANIMALS

11 client-owned dogs with idiopathic epilepsy and ≥ 2 generalized seizures/mon that were currently being treated with ≥ 2 antiepileptic drugs.

PROCEDURES

Telmisartan was administered at a dosage of 0.25 to 1 mg/kg, PO, every 12 hours for 4 to 16 months. Seizure frequencies before and during telmisartan treatment were recorded.

RESULTS

10 dogs completed the 4-month treatment protocol. One dog was excluded owing to a transient increase in serum creatinine concentration; no adverse effects of telmisartan were observed in the remaining 10 dogs. A reduction in seizure frequency greater than an estimated expected placebo effect of 30% was evident in 7 of the 10 dogs. Long-term (12 to 16 months) follow-up information was available for 6 dogs, of which 4 had a further reduction in seizure frequency. Differences in seizure frequency were not statistically significant. No significant difference was found in serum phenobarbital concentration throughout the treatment period in the 7 dogs that were tested.

CLINICAL RELEVANCE

Telmisartan has the potential to reduce seizure frequency when administered as an add-on antiepileptic drug in dogs with refractory idiopathic epilepsy. A randomized, double-blind, placebo-controlled trial is needed to determine the true efficacy of telmisartan. On the basis of our results, a sample size of 54 dogs with refractory idiopathic epilepsy would be needed.

Blood-Brain Barrier Breakdown in Stress and Neurodegeneration: Biochemical Mechanisms and New Models for Translational Research

Blood-brain barrier (BBB) is a structural and functional element of the neurovascular unit (NVU), which includes cells of neuronal, glial, and endothelial nature. The main functions of NVU include maintenance of the control of metabolism and chemical homeostasis in the brain tissue, ensuring adequate blood flow in active regions, regulation of neuroplasticity processes, which is realized through intercellular interactions under normal conditions, under stress, in neurodegeneration, neuroinfection, and neurodevelopmental diseases. Current versions of the BBB and NVU models, static and dynamic, have significantly expanded research capabilities, but a number of issues remain unresolved, in particular, personification of the models for a patient. In addition, application of both static and dynamic models has an important problem associated with the difficulty in reproducing pathophysiological mechanisms responsible for the damage of the structural and functional integrity of the barrier in the diseases of the central nervous system. More knowledge on the cellular and molecular mechanisms of BBB and NVU damage in pathology is required to solve this problem. This review discusses current state of the cellular and molecular mechanisms that control BBB permeability, pathobiochemical mechanisms and manifestations of BBB breakdown in stress and neurodegenerative diseases, as well as the problems and prospects of creating in vitro BBB and NVU models for translational studies in neurology and neuropharmacology. Deciphering BBB (patho)physiology will open up new opportunities for further development in the related areas of medicine such as regenerative medicine, neuropharmacology, and neurorehabilitation.

Influence of metabolic syndrome on post-stroke outcome, angiogenesis and vascular function in old rats determined by dynamic contrast enhanced MRI

Stroke affects primarily aged and co-morbid people, aspects not properly considered to date. Since angiogenesis/vasculogenesis are key processes for stroke recovery, we purposed to determine how different co-morbidities affect the outcome and angiogenesis/vasculogenesis, using a rodent model of metabolic syndrome, and by dynamic enhanced-contrast imaging (DCE-MRI) to assess its non-invasive potential to determine these processes. Twenty/twenty-two month-old corpulent (JCR:LA-Cp/Cp), a model of metabolic syndrome and lean rats were used. After inducing the experimental ischemia by transient MCAO, angiogenesis was analyzed by histology, vasculogenesis by determination of endothelial progenitor cells in peripheral blood by flow cytometry and evaluating their pro-angiogenic properties in culture and the vascular function by DCE-MRI at 3, 7 and 28 days after tMCAO. Our results show an increased infarct volume, BBB damage and an impaired outcome in corpulent rats compared with their lean counterparts. Corpulent rats also displayed worse post-stroke angiogenesis/vasculogenesis, outcome that translated in an impaired vascular function determined by DCE-MRI. These data confirm that outcome and angiogenesis/vasculogenesis induced by stroke in old rats are negatively affected by the co-morbidities present in the corpulent genotype and also that DCE-MRI might be a technique useful for the non-invasive evaluation of vascular function and angiogenesis processes.

Endothelial SIRT6 blunts stroke size and neurological deficit by preserving blood-brain barrier integrity: a translational study

AIMS

Aging is an established risk factor for stroke; genes regulating longevity are implicated in the pathogenesis of ischaemic stroke where to date, therapeutic options remain limited. The blood-brain barrier (BBB) is crucially involved in ischaemia/reperfusion (I/R) brain injury thus representing an attractive target for developing novel therapeutic agents. Given the role of endothelial cells in the BBB, we hypothesized that the endothelial-specific expression of the recently described longevity gene SIRT6 may exhibit protective properties in stroke.

METHODS AND RESULTS

SIRT6 endothelial expression was reduced following stroke. Endothelial-specific Sirt6 knockout (eSirt6-/-) mice, as well as animals in which Sirt6 overexpression was post-ischaemically induced, underwent transient middle cerebral artery occlusion (tMCAO). eSirt6-/- animals displayed increased infarct volumes, mortality, and neurological deficit after tMCAO, as compared to control littermates. Conversely, post-ischaemic Sirt6 overexpression decreased infarct size and neurological deficit. Analysis of ischaemic brain sections revealed increased BBB damage and endothelial expression of cleaved caspase-3 in eSIRT6-/- mice as compared to controls. In primary human brain microvascular endothelial cells (HBMVECs), hypoxia/reoxygenation (H/R) reduced SIRT6 expression and SIRT6 silencing impaired the barrier function (transendothelial resistance) similar to what was observed in mice exposed to I/R. Further, SIRT6-silenced HBMVECs exposed to H/R showed reduced viability, increased cleaved caspase-3 expression and reduced activation of the survival pathway Akt. In ischaemic stroke patients, SIRT6 expression was higher in those with short-term neurological improvement as assessed by NIHSS scale and correlated with stroke outcome.

CONCLUSION

Endothelial SIRT6 exerts a protective role in ischaemic stroke by blunting I/R-mediated BBB damage and thus, it may represent an interesting novel therapeutic target to be explored in future clinical investigation.

Non-Invasive Low Pulsed Electrical Fields for Inducing BBB Disruption in Mice-Feasibility Demonstration

The blood–brain barrier (BBB) is a major hurdle for the treatment of central nervous system disorders, limiting passage of both small and large therapeutic agents from the blood stream into the brain. Thus, means for inducing BBB disruption (BBBd) are urgently needed. Here, we studied the application of low pulsed electrical fields (PEFs) for inducing BBBd in mice. Mice were treated by low PEFs using electrodes pressed against both sides of the skull (100–400 square 50 µs pulses at 4 Hz with different voltages). BBBd as a function of treatment parameters was evaluated using MRI-based treatment response assessment maps (TRAMs) and Evans blue extravasation. A 3D numerical model of the mouse brain and electrodes was constructed using finite element software, simulating the electric fields distribution in the brain and ensuring no significant temperature elevation. BBBd was demonstrated immediately after treatment and significant linear regressions were found between treatment parameters and the extent of BBBd. The maximal induced electric field in the mice brains, calculated by the numerical model, ranged between 62.4 and 187.2 V/cm for the minimal and maximal applied voltages. These results demonstrate the feasibility of inducing significant BBBd using non-invasive low PEFs, well below the threshold for electroporation.

Mechanisms of Blood-Brain Barrier Dysfunction in Traumatic Brain Injury

Traumatic brain injuries (TBIs) account for the majority of injury-related deaths in the United States with roughly two million TBIs occurring annually. Due to the spectrum of severity and heterogeneity in TBIs, investigation into the secondary injury is necessary in order to formulate an effective treatment. A mechanical consequence of trauma involves dysregulation of the blood–brain barrier (BBB) which contributes to secondary injury and exposure of peripheral components to the brain parenchyma. Recent studies have shed light on the mechanisms of BBB breakdown in TBI including novel intracellular signaling and cell–cell interactions within the BBB niche. The current review provides an overview of the BBB, novel detection methods for disruption, and the cellular and molecular mechanisms implicated in regulating its stability following TBI.

Harmonizing brain magnetic resonance imaging methods for vascular contributions to neurodegeneration

INTRODUCTION

Many consequences of cerebrovascular disease are identifiable by magnetic resonance imaging (MRI), but variation in methods limits multicenter studies and pooling of data. The European Union Joint Program on Neurodegenerative Diseases (EU JPND) funded the HARmoNizing Brain Imaging MEthodS for VaScular Contributions to Neurodegeneration (HARNESS) initiative, with a focus on cerebral small vessel disease.

METHODS

Surveys, teleconferences, and an in-person workshop were used to identify gaps in knowledge and to develop tools for harmonizing imaging and analysis.

RESULTS

A framework for neuroimaging biomarker development was developed based on validating repeatability and reproducibility, biological principles, and feasibility of implementation. The status of current MRI biomarkers was reviewed. A website was created at www.harness-neuroimaging.org with acquisition protocols, a software database, rating scales and case report forms, and a deidentified MRI repository.

CONCLUSIONS

The HARNESS initiative provides resources to reduce variability in measurement in MRI studies of cerebral small vessel disease.

Quantifying blood-brain barrier leakage in small vessel disease: Review and consensus recommendations

Cerebral small vessel disease (cSVD) comprises pathological processes of the small vessels in the brain that may manifest clinically as stroke, cognitive impairment, dementia, or gait disturbance. It is generally accepted that endothelial dysfunction, including blood-brain barrier (BBB) failure, is pivotal in the pathophysiology. Recent years have seen increasing use of imaging, primarily dynamic contrast-enhanced magnetic resonance imaging, to assess BBB leakage, but there is considerable variability in the approaches and findings reported in the literature. Although dynamic contrast-enhanced magnetic resonance imaging is well established, challenges emerge in cSVD because of the subtle nature of BBB impairment. The purpose of this work, authored by members of the HARNESS Initiative, is to provide an in-depth review and position statement on magnetic resonance imaging measurement of subtle BBB leakage in clinical research studies, with aspects requiring further research identified. We further aim to provide information and consensus recommendations for new investigators wishing to study BBB failure in cSVD and dementia.

Radiation injury versus malignancy after stereotactic radiosurgery for brain metastases: impact of time-dependent changes in lesion morphology on MRI

Background

We sought to determine whether radiation-induced injuries could be distinguished from malignancy after stereotactic radiosurgery (SRS) by analyzing time-dependent changes in lesion morphology on sequential MRI for up to 55min.

Methods

In 31 consecutive patients treated with SRS for brain metastases, the time-dependent changes in lesion morphology were analyzed on MRI 2min, 15min, and 55min after contrast administration and on subtraction images. A simultaneous, matched-pairs approach was used for quantitative region of interest analysis of the area of the lesion. Qualitative analysis comprised the shape of the border, the structure of the interior area, the presence of leptomeningeal enhancement, and feeding vessels. The signal intensity changes of the border and the interior area of the lesions over time were assessed visually. The time-dependent changes in the 2 entities were compared.

Results

Twenty radiation-induced injuries and 21 malignancies were analyzed. A significant interaction effect between time point and diagnosis (P<.001) was found for the time-dependent changes of the margin of the lesion for 2min to 15min and in signal intensity differences of the rim and interior area as well as of the size of the interior area for up to 55min. All radiation-induced injuries showed a black interior area on the subtraction images for 15min minus 55min, whereas all malignant lesions had white components (P<.001).

Conclusions

Analysis of time-dependent changes in lesion morphology on sequential MRI for up to 55min is a reliable tool to distinguish radiation-induced injuries from malignancy after SRS.

TSPO imaging using the novel PET ligand [18F]GE-180: quantification approaches in patients with multiple sclerosis

Background

PET ligands targeting the translocator protein (TSPO) represent promising tools to visualise neuroinflammation. Here, we analysed parameters obtained in dynamic and static PET images using the novel TSPO ligand [¹⁸F]GE-180 in patients with relapsing remitting multiple sclerosis (RRMS) and an approach for semi-quantitative assessment of this disease in clinical routine.

Seventeen dynamic [¹⁸F]GE-180 PET scans of RRMS patients were evaluated (90 min). A pseudo-reference region (PRR) was defined after identification of the least disease-affected brain area by voxel-based comparison with six healthy controls (HC) and upon exclusion of voxels suspected of being affected in static 60–90 min p.i. images. Standardised uptake value ratios (SUVR) obtained from static images normalised to PRR were correlated to the distribution volume ratios (DVR) derived from dynamic data with Logan reference tissue model.

Results

Group comparison with HC revealed white matter and thalamus as most affected regions. Fewest differences were found in grey matter, and normalisation to frontal cortex (FC) yielded the greatest reduction in variability of healthy grey and white matter. Hence, FC corrected for affected voxels was chosen as PRR, leading to time-activity curves of FC which were congruent to HC data (SUV_60–90 0.37, U test P = 0.42). SUVR showed a very strong correlation with DVR (Pearson ρ > 0.9). Focal MS lesions exhibited a high SUVR (range, 1.3–3.2).

Conclusions

This comparison with parameters from dynamic data suggests that SUVR normalised to corrected frontal cortex as PRR is suitable for the quantification of [¹⁸F]GE-180 uptake in lesions and different brain regions of RRMS patients. This efficient diagnostic protocol based on static [¹⁸F]GE-180 PET scans acquired 60–90 min p.i. allows the semi-quantitative assessment of neuroinflammation in RRMS patients in clinical routine.

Microvascular anomaly conditions in psychiatric disease. Schizophrenia - angiogenesis connection

Schizophrenia (SZ) is a severe mental disorder with unknown etiology and elusive neuropathological and neurobiological features have been a focus of many theoretical hypotheses and empirical studies. Current genetic and neurobiology information relevant to SZ implicates neuronal developmental and synaptic plasticity abnormalities, and neurotransmitter, microglial and oligodendrocytes dysfunction. Several recent theories have highlighted the neurovascular unit as a potential contributor to the pathophysiology of SZ. We explored the biological plausibility of a link between SZ and the neurovascular system by examining insights gained from genetic, neuroimaging and postmortem studies, which include gene expression and neuropathology analyses. We also reviewed information from animal models of cerebral angiogenesis in order to understand better the complex interplay between angiogenic and neurotrophic factors in development, vascular endothelium/blood brain barrier remodeling and maintenance, all of which contribute to sustaining adequate regional blood flow and safeguarding normal brain function. Microvascular and hemodynamic alterations in SZ highlight the importance of further research and reveal the neurovascular unit as a potential therapeutic target in SZ.

Microvascular anomaly conditions in psychiatric disease. Schizophrenia - angiogenesis connection

Schizophrenia (SZ) is a severe mental disorder with unknown etiology and elusive neuropathological and neurobiological features have been a focus of many theoretical hypotheses and empirical studies. Current genetic and neurobiology information relevant to SZ implicates neuronal developmental and synaptic plasticity abnormalities, and neurotransmitter, microglial and oligodendrocytes dysfunction. Several recent theories have highlighted the neurovascular unit as a potential contributor to the pathophysiology of SZ. We explored the biological plausibility of a link between SZ and the neurovascular system by examining insights gained from genetic, neuroimaging and postmortem studies, which include gene expression and neuropathology analyses. We also reviewed information from animal models of cerebral angiogenesis in order to understand better the complex interplay between angiogenic and neurotrophic factors in development, vascular endothelium/blood brain barrier remodeling and maintenance, all of which contribute to sustaining adequate regional blood flow and safeguarding normal brain function. Microvascular and hemodynamic alterations in SZ highlight the importance of further research and reveal the neurovascular unit as a potential therapeutic target in SZ.

Blood-Brain Barrier Protection as a Therapeutic Strategy for Acute Ischemic Stroke

The blood-brain barrier (BBB) is a vital component of the neurovascular unit (NVU) containing tight junctional (TJ) proteins and different ion and nutrient transporters which maintain normal brain physiology. BBB disruption is a major pathological hallmark in the course of ischemic stroke which is regulated by the actions of different factors working at different stages of cerebral ischemia including matrix metalloproteinases (MMPs), inflammatory modulators, vesicular trafficking, oxidative pathways, and junctional-cytoskeletal interactions. These components interact further to disrupt maintenance of both the paracellular and transport barriers of the central nervous system (CNS) to worsen ischemic brain injury and the propensity for hemorrhagic transformation (HT) associated with injury and/or thrombolytic therapy with tissue-type plasminogen activator (tPA). We propose that these complex molecular pathways should be evaluated further so that they could be targeted alone or in combination to protect the BBB during cerebral ischemia. These types of novel interventions should be guided by advanced imaging techniques for better diagnosis of BBB damage which may exert significant therapeutic benefit including the extension of therapeutic window of tPA. This review will focus on the different stages and mechanisms of BBB damage in acute ischemic stroke and novel therapeutic strategies to target those pathways for better therapeutic outcome in stroke.

Acid fibroblast growth factor preserves blood-brain barrier integrity by activating the PI3K-Akt-Rac1 pathway and inhibiting RhoA following traumatic brain injury

The blood-brain barrier (BBB) plays important roles in the recovery of traumatic brain injury (TBI) which is a major factor contributing to cerebral edema. Acid fibroblast growth factor (aFGF) contributes to maintain vascular integrity and restores nerve function. However, whether aFGF protects BBB following TBI remains unknown. The purpose of this study was to determine whether exogenous aFGF preserves BBB integrity by activating the PI3K-Akt-Rac1 pathway and inhibiting RhoA after TBI. BBB permeability was assessed using evans blue dye and fluorescein isothiocyanate dextran fluorescence. Neurofunctional tests, such as the garcia test, were conducted in a blinded fashion, and protein expression was evaluated via western blotting and immunofluorescence staining. Our results showed that aFGF improved neurofunctional deficits, preserved BBB integrity, and up-regulated tight junction proteins and adherens junction proteins 24 h after experimental TBI. However, the PI3K/Akt inhibitor LY294002 reversed the protective effects of aFGF on neurofunctional deficits and junction protein expression and significantly suppressed p-Akt and GTP-Rac1 activity. Furthermore, aFGF administration significantly decreased GTP-RhoA expression in the treated group compared with the vehicle group, while PI3K/Akt inhibition increased GTP-RhoA expression. Similar results were observed in vitro, as aFGF exerted protective effects on endothelial cell integrity by up-regulating junction proteins and PI3K-Akt-Rac1 pathway and down-regulating RhoA expression under oxygen-glucose deprivation/reoxygenation (OGD) conditions. These data suggest that exogenous aFGF reduces RhoA activity in part by activating the PI3K-Akt-Rac1 signaling pathway, thus improving neurofunctional deficits and preserving BBB integrity after TBI.

Evolution of blood-brain-barrier permeability after acute ischemic stroke

The dynamics of BBB permeability after AIS in humans are not well understood. In the present study we measured the evolution of BBB permeability after AIS in humans using MRI. Patients presenting to our institution with a diagnosis of AIS underwent a single dynamic contrast-enhanced MRI (DCE-MRI) sequence to measure BBB permeability during their initial workup. Forty-two patients were included in the final analysis. The patient sample underwent DCE-MRI at a mean time of 23.8hrs after the onset of AIS symptoms (range: 1.3–90.7hrs). At all time-points the BBB permeability within the infarct region of the brain as defined on DWI/ADC was higher compared to the homologous region of the contralateral hemisphere (p<0.005). BBB permeability, expressed as a ratio of infarct permeability to contralateral permeability, was greatest at 6-48hrs after the onset of AIS. Although the data was not acquired longitudinally, these findings suggest that the permeability of the BBB is continually elevated following AIS, which contradicts previous assertions that BBB permeability after AIS follows a biphasic course. Knowledge of BBB dynamics following AIS may provide insight into future treatments for AIS, especially BBB stabilizing agents.

Blood-Brain Barrier Disruption After Cardiopulmonary Bypass: Diagnosis and Correlation to Cognition

BACKGROUND

Cardiopulmonary bypass (CPB) elicits a systemic inflammatory response that may impair blood-brain barrier (BBB) integrity. BBB disruption can currently be detected by dynamic contrast enhancement magnetic resonance imaging (MRI), reflected by an increase in the permeability constant (K^trans). We aimed to determine (1) whether CPB induces BBB disruption, (2) duration until BBB disruption resolution, and (3) the obtainable correlation between BBB injury (location and intensity) and neurocognitive dysfunction.

METHODS

Seven patients undergoing CPB with coronary artery bypass grafting (CABG) were assigned to serial cerebral designated MRI evaluations, preoperatively and on postoperative day (POD) 1 and 5. Examinations were analyzed for BBB disruption and microemboli using dynamic contrast enhancement MRI and diffusion-weighted imaging methods, respectively. Neuropsychologic tests were performed 1 day preoperatively and on POD 5.

RESULTS

A significant local K^trans increase (0.03 min^-1 vs 0.07 min^-1, p = 0.033) compatible with BBB disruption was evident in 5 patients (71%) on POD 1. Resolution was observed by POD 5 (mean, 0.012 min^-1). The location of the disruption was most prominent in the frontal lobes (400% vs 150% K^trans levels upsurge, p = 0.05). MRI evidence of microembolization was demonstrated in only 1 patient (14%). The postoperative global cognitive score was reduced in all patients (98.2 ± 12 vs 95.1 ± 11, p = 0.032), predominantly in executive and attention (frontal lobe-related) functions (91.8 ± 13 vs 86.9 ± 12, p = 0.042). The intensity of the dynamic contrast enhancement MRI BBB impairment correlated with the magnitude of cognition reduction (r = 0.69, p = 0.04).

CONCLUSIONS

BBB disruption was evident in most patients, primarily in the frontal lobes. The location and intensity of the BBB disruption, rather than the microembolic load, correlated with postoperative neurocognitive dysfunction.

DCE-MRI blood–brain barrier assessment in acute ischemic stroke

Objective:

To quantitatively evaluate blood–brain barrier changes in ischemic stroke patients using dynamic contrast-enhanced (DCE) MRI.

Methods:

We examined 54 stroke patients (clinicaltrials.govNCT00715533, NCT02077582) in a 3T MRI scanner within 48 hours after symptom onset. Twenty-eight patients had a follow-up examination on day 5–7. DCE T1 mapping and Patlak analysis were employed to assess BBB permeability changes.

Results:

Median stroke Ktrans values (0.7 × 10−3 min−1 [interquartile range (IQR) 0.4–1.8] × 10−3 min−1) were more than 3-fold higher compared to median mirror Ktrans values (0.2 × 10−3 min−1, IQR 0.1–0.7 × 10−3 min−1, p < 0.001) and further increased at follow-up (n = 28, 2.3 × 10−3 min−1, IQR 0.8–4.6 × 10−3 min−1, p < 0.001). By contrast, mirror Ktrans values decreased over time with a clear interaction of timepoint and stroke/mirror side (p < 0.001). Median stroke Ktrans values were 2.5 times lower than in hemorrhagic transformed regions (0.7 vs 1.8 × 10−3 min−1; p = 0.055). There was no association between stroke Ktrans values and the delay from symptom onset to baseline examination, age, and presence of hyperintense acute reperfusion marker.

Conclusion:

BBB in acute stroke patients can be successfully assessed quantitatively. The decrease of BBB permeability in unaffected regions at follow-up may be an indicator of global BBB leakage even in vessel territories remote from the index infarct.

Dynamic contrast-enhanced MRI and CT provide comparable measurement of blood-brain barrier permeability in a rodent stroke model

In the current management of acute ischemic stroke (AIS), clinical criteria are used to estimate the risk of hemorrhagic transformation (HT), which is a devastating early complication. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and computed tomography (DCE-CT) may serve as physiologically-based decision making tools to more reliably assess the risk of HT. Before these tools can be properly validated, the comparability of the blood-brain barrier (BBB) permeability measurements they generate should be assessed. Sixteen rats were subjected to a transient middle cerebral artery occlusion before successively undergoing DCE-CT and DCE-MRI at 24-hours. BBB permeability (K(trans)) values were generated from both modalities. A correlation of R=0.677 was found (p<0.01) and the resulting relationship was [DCE-CT=(0.610*DCE-MRI)+4.140]. A variance components analysis found the intra-rat coefficient of variation to be 0.384 and 0.258 for K(trans) values from DCE-MRI and DCE-CT respectively. Permeability measures from DCE-CT were 22% higher than those from DCE-MRI. The results of this study demonstrate for the first time comparability between DCE-CT and DCE-MRI in the assessment of AIS. These results may provide a foundation for future clinical trials making combined use of these modalities.

Delayed contrast extravasation MRI: a new paradigm in neuro-oncology

BACKGROUND

Conventional magnetic resonance imaging (MRI) is unable to differentiate tumor/nontumor enhancing tissues. We have applied delayed-contrast MRI for calculating high resolution treatment response assessment maps (TRAMs) clearly differentiating tumor/nontumor tissues in brain tumor patients.

METHODS

One hundred and fifty patients with primary/metastatic tumors were recruited and scanned by delayed-contrast MRI and perfusion MRI. Of those, 47 patients underwent resection during their participation in the study. Region of interest/threshold analysis was performed on the TRAMs and on relative cerebral blood volume maps, and correlation with histology was studied. Relative cerebral blood volume was also assessed by the study neuroradiologist.

RESULTS

Histological validation confirmed that regions of contrast agent clearance in the TRAMs >1 h post contrast injection represent active tumor, while regions of contrast accumulation represent nontumor tissues with 100% sensitivity and 92% positive predictive value to active tumor. Significant correlation was found between tumor burden in the TRAMs and histology in a subgroup of lesions resected en bloc (r(2) = 0.90, P < .0001). Relative cerebral blood volume yielded sensitivity/positive predictive values of 51%/96% and there was no correlation with tumor burden. The feasibility of applying the TRAMs for differentiating progression from treatment effects, depicting tumor within hemorrhages, and detecting residual tumor postsurgery is demonstrated.

CONCLUSIONS

The TRAMs present a novel model-independent approach providing efficient separation between tumor/nontumor tissues by adding a short MRI scan >1 h post contrast injection. The methodology uses robust acquisition sequences, providing high resolution and easy to interpret maps with minimal sensitivity to susceptibility artifacts. The presented results provide histological validation of the TRAMs and demonstrate their potential contribution to the management of brain tumor patients.

Blood brain barrier and neuroinflammation are critical targets of IGF-1-mediated neuroprotection in stroke for middle-aged female rats

Ischemia-induced cerebral infarction is more severe in older animals as compared to younger animals, and is associated with reduced availability of insulin-like growth factor (IGF)-1. This study determined the effect of post-stroke IGF-1 treatment, and used microRNA profiling to identify mechanisms underlying IGF-1’s neuroprotective actions. Post-stroke ICV administration of IGF-1 to middle-aged female rats reduced infarct volume by 39% when measured 24h later. MicroRNA analyses of ischemic tissue collected at the early post-stroke phase (4h) indicated that 8 out of 168 disease-related miRNA were significantly downregulated by IGF-1. KEGG pathway analysis implicated these miRNA in PI3K-Akt signaling, cell adhesion/ECM receptor pathways and T-and B-cell signaling. Specific components of these pathways were subsequently analyzed in vehicle and IGF-1 treated middle-aged females. Phospho-Akt was reduced by ischemia at 4h, but elevated by IGF-1 treatment at 24h. IGF-1 induced Akt activation was preceded by a reduction of blood brain barrier permeability at 4h post-stroke and global suppression of cytokines including IL-6, IL-10 and TNF-α. A subset of these cytokines including IL-6 was also suppressed by IGF-1 at 24h post-stroke. These data are the first to show that the temporal and mechanistic components of post-stroke IGF-1 treatment in older animals, and that cellular components of the blood brain barrier may serve as critical targets of IGF-1 in the aging brain.

Treadmill pre-training ameliorates brain edema in ischemic stroke via down-regulation of aquaporin-4: an MRI study in rats

Objective

Treadmill pre-training can ameliorate blood brain barrier (BBB) dysfunction in ischemia-reperfusion injury, however, its role in ischemic brain edema remains unclear. This study assessed the neuroprotective effects induced by treadmill pre-training, particularly on brain edema in transient middle cerebral artery occluded model.

Methods

Transient middle cerebral artery occlusion to induce stroke was performed on rats after 2 weeks of treadmill pre-training. Magnetic resonance imaging (MRI) was used to evaluate the dynamic impairment of cerebral edema after ischemia-reperfusion injury. In addition, measurements of wet and dry brain weight, Evans Blue assay and Garcia scores were performed to investigate the cerebral water content, BBB permeability and neurologic deficit, respectively. Moreover, during ischemia-reperfusion injury, the expression of Aquaporin 4 (AQP4) was detected using immunofluorescence and Western bloting analyses.

Results

Treadmill pre-training improved the relative apparent diffusion coefficient (rADC) loss in the ipsilateral cortex and striatum at 1 hour and 2.5 hours after cerebral ischemia. In the treadmill pre-training group, T2W1 values of the ipsilateral cortex and striatum increased less at 7.5 hours, 1 day, and 2 days after stroke while the brain water content decreased at 2 days after ischemia. Regarding the BBB permeability, the semi-quantitative amount of contrast agent leakage of treadmill pre-training group significantly decreased. Less Evans Blue exudation was also observed in treadmill pre-training group at 2 days after stroke. In addition, treadmill pre-training mitigated the Garcia score deficits at 2 days after stroke. Immunofluorescence staining and Western blotting results showed a significant decrease in the expression of AQP4 after treadmill ischemia following pre-training.

Conclusions

Treadmill pre-training may reduce cerebral edema and BBB dysfunction during cerebral ischemia/reperfusion injury via the down-regulation of AQP4.

Delayed contrast extravasation MRI for depicting tumor and non-tumoral tissues in primary and metastatic brain tumors

The current standard of care for newly diagnosed glioblastoma multiforme (GBM) is resection followed by radiotherapy with concomitant and adjuvant temozolomide. Recent studies suggest that nearly half of the patients with early radiological deterioration post treatment do not suffer from tumor recurrence but from pseudoprogression. Similarly, a significant number of patients with brain metastases suffer from radiation necrosis following radiation treatments. Conventional MRI is currently unable to differentiate tumor progression from treatment-induced effects. The ability to clearly differentiate tumor from non-tumoral tissues is crucial for appropriate patient management. Ten patients with primary brain tumors and 10 patients with brain metastases were scanned by delayed contrast extravasation MRI prior to surgery. Enhancement subtraction maps calculated from high resolution MR images acquired up to 75 min after contrast administration were used for obtaining stereotactic biopsies. Histological assessment was then compared with the pre-surgical calculated maps. In addition, the application of our maps for prediction of progression was studied in a small cohort of 13 newly diagnosed GBM patients undergoing standard chemoradiation and followed up to 19.7 months post therapy. The maps showed two primary enhancement populations: the slow population where contrast clearance from the tissue was slower than contrast accumulation and the fast population where clearance was faster than accumulation. Comparison with histology confirmed the fast population to consist of morphologically active tumor and the slow population to consist of non-tumoral tissues. Our maps demonstrated significant correlation with perfusion-weighted MR data acquired simultaneously, although contradicting examples were shown. Preliminary results suggest that early changes in the fast volumes may serve as a predictor for time to progression. These preliminary results suggest that our high resolution MRI-based delayed enhancement subtraction maps may be applied for clear depiction of tumor and non-tumoral tissues in patients with primary brain tumors and patients with brain metastases.

Extracellular matrix and matrix receptors in blood-brain barrier formation and stroke

The blood-brain barrier (BBB) is formed primarily to protect the brain microenvironment from the influx of plasma components, which may disturb neuronal functions. The BBB is a functional unit that consists mainly of specialized endothelial cells (ECs) lining the cerebral blood vessels, astrocytes, and pericytes. The BBB is a dynamic structure that is altered in neurologic diseases, such as stroke. ECs and astrocytes secrete extracellular matrix (ECM) proteins to generate and maintain the basement membranes (BMs). ECM receptors, such as integrins and dystroglycan, are also expressed at the brain microvasculature and mediate the connections between cellular and matrix components in physiology and disease. ECM proteins and receptors elicit diverse molecular signals that allow cell adaptation to environmental changes and regulate growth and cell motility. The composition of the ECM is altered upon BBB disruption and directly affects the progression of neurologic disease. The purpose of this review is to discuss the dynamic changes of ECM composition and integrin receptor expression that control BBB functions in physiology and pathology.

Neuroinflammation and cerebrovascular disease in old age: a translational medicine perspective

The incidence of cerebrovascular disease is highest in the elderly population. However, the pathophysiological mechanisms of brain response to cerebral ischemia in old age are currently poorly understood. Ischemic changes in the commonly used young animal stroke models do not reflect the molecular changes associated with the aged brain. Neuroinflammation and oxidative stress are important pathogenic processes occurring during the acute phase of cerebral ischemia. Free radical generation is also implicated in the aging process, and the combination of these effects in elderly stroke patients could explain the higher risk of morbidity and mortality. A better understanding of stroke pathophysiology in the elderly patient would assist in the development of new therapeutic strategies for this vulnerable age group. With the increasing use of reperfusion therapies, inflammatory pathways and oxidative stress remain attractive therapeutic targets for the development of adjuvant neuroprotective agents. This paper will discuss these molecular aspects of acute stroke and senescence from a bench-to-bedside research perspective.

Neurological imaging: statistics behind the pictures

Neurological imaging represents a powerful paradigm for investigation of brain structure, physiology and function across different scales. The diverse phenotypes and significant normal and pathological brain variability demand reliable and efficient statistical methodologies to model, analyze and interpret raw neurological images and derived geometric information from these images. The validity, reproducibility and power of any statistical brain map require appropriate inference on large cohorts, significant community validation, and multidisciplinary collaborations between physicians, engineers and statisticians.