Changes In Blood-brain Barrier Integrity Research Articles

Neighborhood disadvantage is associated with changes in cerebrovascular function among older adults over a 9 year follow‐up period

AbstractBackgroundStressful social environments exert a strong influence on unhealthy aging, both in greater magnitude and independent of individual socioeconomic and lifestyle factors. Neighborhood disadvantage specifically has been linked to accelerated biological aging, cognitive decline, and core Alzheimer’s disease (AD) neuropathology, but little is known about whether neighborhood disadvantage contributes to cerebrovascular dysfunction commonly observed in aging and AD. We examine whether neighborhood disadvantage relates to changes in cerebrovascular outcomes over time, including blood‐brain barrier (BBB) integrity, cerebral blood flow (CBF), and small vessel disease (SVD) biomarkers.MethodsVanderbilt Memory and Aging Project participants (n = 296, 73±7 years, 40% female) underwent fasting blood and cerebrospinal fluid (CSF) acquisition serially over a 9‐year follow‐up period (mean follow‐up = 5.5 years). Area Deprivation Index (ADI), representing neighborhood disadvantage, was quantified at baseline based on 17 components [e.g., housing, income, education, and household characteristics (Kind & Buckingham, 2018)]. BBB markers (MMP‐2, MMP‐3, MMP‐9, TIMP‐1, TIMP‐2, PDGFRβ) were quantified from CSF and CSF/plasma albumin ratio was quantified from both CSF and plasma. 3T multimodal MRI images were used to quantify grey matter CBF and SVD markers, including white matter hyperintensities (WMHs), perivascular spaces (PVS), and lacunes. Linear mixed effects regression models related time x ADI to longitudinal BBB, CBF, and SVD outcomes adjusting for age, sex, race/ethnicity, education, cognitive status, Framingham Stroke Risk Profile (minus age), apolipoprotein ε4 status, and follow‐up time. CBF models additionally adjusted for corresponding grey matter volume while SVD models adjusted for T1‐weighted intracranial volume.ResultsBaseline ADI related to increased MMP‐9 (β = 0.03, p‐value = 0.01) and decreased PDGFRβ (β = ‐0.1407, p‐value<0.05) over time but unrelated to longitudinal changes in CBF (p‐values>0.35), SVD (p‐values>0.36), or other BBB outcomes (p‐values>0.07).ConclusionsNeighborhood socioeconomic disadvantage relates to changes in BBB integrity among older adults over time, particularly molecular markers of barrier disruption and pericyte damage. Findings support the hypothesis that adverse environmental conditions, including low quality housing and community‐wide resource constraints, may contribute to early‐stage cerebrovascular dysfunction beyond individual socioeconomic and lifestyle factors.FundingHHMI James H. Gilliam Fellowship for Advanced Study; IIRG‐08‐88733; R01‐AG034962; R01‐AG056534; K24‐AG046373; P20‐AG068

DDEL-14. EXPLORING THE ROLE OF WNT PATHWAY INHIBITION ON GLIOMA STEM CELLS PROGRESSION AND BRAIN ENDOTHELIAL INTEGRITY

Abstract The blood–brain barrier (BBB) is a specialized neurovascular unit evolved to maintain brain homeostasis and prevent effective agents from reaching malignant brain tumors such as glioblastoma. The Wnt/β-catenin signaling pathway helps to ensure BBB integrity and previous studies demonstrate Wnt pathway inhibition increases BBB permeability. High grade gliomas express increased Wnt expression compared with normal tissue. We hypothesize that Wnt pathway inhibition in glioma stem cells (GSCs) will hinder progression, increase BBB permeability, and enhance overall treatment response. In this study, we transduced primary pediatric-derived glioma stem cells with lentiviral vectors overexpressing Wnt inhibitors (DKK1 or WIF1) and then characterized migration, proliferation, and cell cycle progression. WNT inhibition on brain endothelial cell integrity was evaluated with GSC conditioned media (GSC-CM) +/- CHIR99021 (Wnt pathway activator) for function via electrical cell-cell impedance and junctional expression. Wnt inhibitor overexpression was verified using RNAseq, proteomic analysis, and immunoblotting. We found that GSC-DKK1 demonstrated significantly decreased cell migration (p< 0.005) and proliferation (p< 0.0001). We also found that CHIR99021 treated GSC-CM endothelial cells displayed decreased tight junctional proteins and increased fenestration protein expression (p< 0.0005), correlating with a more porous endothelium. Overall, our studies showed Wnt inhibitor overexpressing GSCs impaired glioma progression in vitro and indirectly disrupted endothelial cell integrity. Future studies will evaluate orthotopic Wnt inhibitor overexpressing transplant rodent models to assess changes in BBB integrity, drug permeability, model survival, and treatment response. Further understanding of the Wnt pathway in both GSCs and the BBB has the potential for improved central nervous system treatment penetration and prolonged disease response.

Zika virus E protein modulates functions of human brain microvascular endothelial cells and astrocytes: implications on blood-brain barrier properties.

Neurotropic viruses can cross the otherwise dynamically regulated blood-brain barrier (BBB) and affect the brain cells. Zika virus (ZIKV) is an enveloped neurotropic Flavivirus known to cause severe neurological complications, such as encephalitis and fetal microcephaly. In the present study, we employed human brain microvascular endothelial cells (hBMECs) and astrocytes derived from human progenitors to establish a physiologically relevant BBB model. We used this model to investigate the effects of ZIKV envelope (E) protein on properties of cells comprising the BBB. E protein is the principal viral protein involved in interaction with host cell surface receptors, facilitating the viral entry. Our findings show that the presence of ZIKV E protein leads to activation of both hBMECs and astrocytes. In hBMECs, we observed a decrease in the expression of crucial endothelial junction proteins such as ZO-1, Occludin and VE-Cadherin, which are vital in establishment and maintenance of the BBB. Consequently, the ZIKV E protein induced changes in BBB integrity and permeability. We also found upregulation of genes involved in leukocyte recruitment along with increased proinflammatory chemokines and cytokines upon exposure to E protein. Additionally, the E protein also led to astrogliosis, evident from the elevated expression of GFAP and Vimentin. Both cell types comprising the BBB exhibited inflammatory response upon exposure to E protein which may influence viral access into the central nervous system (CNS) and subsequent infection of other CNS cells. Overall, our study provides valuable insights into the transient changes that occur at the site of BBB upon ZIKV infection.

N-acetylcysteine Amide Ameliorates Blast-Induced Changes in Blood-Brain Barrier Integrity in Rats.

Traumatic brain injury resulting from exposure to blast overpressure (BOP) is associated with neuropathology including impairment of the blood-brain barrier (BBB). This study examined the effects of repeated exposure to primary BOP and post-blast treatment with an antioxidant, N-acetylcysteine amide (NACA) on the integrity of BBB. Anesthetized rats were exposed to three 110 kPa BOPs separated by 0.5 h. BBB integrity was examined in vivo via a cranial window allowing imaging of pial microcirculation by intravital microscopy. Tetramethylrhodamine isothiocyanate Dextran (TRITC-Dextran, mw = 40 kDa or 150 kDa) was injected intravenously 2.5 h after the first BOP exposure and the leakage of TRITC-Dextran from pial microvessels into the brain parenchyma was assessed. The animals were randomized into 6 groups (n = 5/group): four groups received 40 kDa TRITC-Dextran (BOP-40, sham-40, BOP-40 NACA, and sham-40 NACA), and two groups received 150 kDa TRITC-Dextran (BOP-150 and sham-150). NACA treated groups were administered NACA 2 h after the first BOP exposure. The rate of TRITC-Dextran leakage was significantly higher in BOP-40 than in sham-40 group. NACA treatment significantly reduced TRITC-Dextran leakage in BOP-40 NACA group and sham-40 NACA group presented the least amount of leakage. The rate of leakage in BOP-150 and sham-150 groups was comparable to sham-40 NACA and thus these groups were not assessed for the effects of NACA. Collectively, these data suggest that BBB integrity is compromised following BOP exposure and that NACA treatment at a single dose may significantly protect against blast-induced BBB breakdown.

Vascular dysfunction—The disregarded partner of Alzheimer's disease

Increasing evidence recognizes Alzheimer's disease (AD) as a multifactorial and heterogeneous disease with multiple contributors to its pathophysiology, including vascular dysfunction. The recently updated AD Research Framework put forth by the National Institute on Aging–Alzheimer's Association describes a biomarker-based pathologic definition of AD focused on amyloid, tau, and neuronal injury. In response to this article, here we first discussed evidence that vascular dysfunction is an important early event in AD pathophysiology. Next, we examined various imaging sequences that could be easily implemented to evaluate different types of vascular dysfunction associated with, and/or contributing to, AD pathophysiology, including changes in blood-brain barrier integrity and cerebral blood flow. Vascular imaging biomarkers of small vessel disease of the brain, which is responsible for >50% of dementia worldwide, including AD, are already established, well characterized, and easy to recognize. We suggest that these vascular biomarkers should be incorporated into the AD Research Framework to gain a better understanding of AD pathophysiology and aid in treatment efforts.

Mechanisms of Blood-Brain Barrier Disruption in Herpes Simplex Encephalitis.

Herpes simplex encephalitis (HSE) is often caused by infection with herpes simplex virus 1 (HSV-1), a neurotropic double-stranded DNA virus. HSE infection always impacts the temporal and frontal lobes or limbic system, leading to edema, hemorrhage, and necrotic changes in the brain parenchyma. Additionally, patients often exhibit severe complications following antiviral treatment, including dementia and epilepsy. HSE is further associated with disruptions to the blood-brain barrier (BBB), which consists of microvascular endothelial cells, tight junctions, astrocytes, pericytes, and basement membranes. Following an HSV-1 infection, changes in BBB integrity and permeability can result in increased movement of viruses, immune cells, and/or cytokines into the brain parenchyma. This leads to an enhanced inflammatory response in the central nervous system and further damage to the brain. Thus, it is important to protect the BBB from pathogens to reduce brain damage from HSE. Here, we discuss HSE and the normal structure and function of the BBB. We also discuss growing evidence indicating an association between BBB breakdown and the pathogenesis of HSE, as well as future research directions and potential new therapeutic targets. Graphical Abstract During herpes simplex encephalitis, the functions and structures of each composition of BBB have been altered by different factors, thus the permeability and integrity of BBB have been broken. The review aim to explore the potential mechanisms and factors in the process, probe the next research targets and new therapeutic targets.

Abstract TP434: Mouse Bilateral Carotid Artery Stenosis Leads to Unexpected Early Changes in Blood-Brain Barrier Integrity

Bilateral carotid artery stenosis (BCAS) is one experimental model of vascular dementia that is thought to preferentially impact brain white matter. Indeed, it is generally accepted that hippocampal and cortical pathology is not observed prior to 30 days post-injury. Since changes in the blood-brain barrier (BBB) permeability are known to precede more overt brain pathology in a variety of diseases, we hypothesized that BBB changes could occur earlier after BCAS in the hippocampus, striatum and cortex and be a precursor of longer term pathology in these regions. In our study, 3 month old male C57/Bl6 mice underwent BCAS with 0.18 mm coils or sham surgery control and changes in BBB were analyzed by collagen IV (vascular basement membrane component), claudin-5 and occludin (tight junction proteins), Evan’s blue (permeability marker), and Ki-67 (marker of cell proliferation) immunohistochemistry, protein and RNA expression levels after 3, 7, 14, or 21 days. Surprisingly, significant changes in markers of cerebrovascular integrity were detected within 7 days compared to sham animals, not only in the striatum but also in the hippocampus. Increased astrocyte and microglia activation was also observed in these regions and TUNEL staining also indicates cell death in the hippocampus within 7 days. While few changes were observed in the cortex, some of the animals did experience cortical ischemic infarcts within 14 days. In conclusion, this study demonstrates for the first time that changes in the BBB occur shortly after BCAS in multiple regions throughout the brain and suggests that such changes might underlie the gradual development of BCAS non-white matter pathology.

Sugammadex-Enhanced Neuronal Apoptosis following Neonatal Sevoflurane Exposure in Mice.

In rodents, neonatal sevoflurane exposure induces neonatal apoptosis in the brain and results in learning deficits. Sugammadex is a new selective neuromuscular blockade (NMB) binding agent that anesthesiologists can use to achieve immediate reversal of an NMB with few side effects. Given its molecular weight of 2178, sugammadex is thought to be unable to pass through the blood brain barrier (BBB). Volatile anesthetics can influence BBB opening and integrity. Therefore, we investigated whether the intraperitoneal administration of sugammadex could exacerbate neuronal damage following neonatal 2% sevoflurane exposure via changes in BBB integrity. Cleaved caspase-3 immunoblotting was used to detect apoptosis, and the ultrastructure of the BBB was examined by transmission electron microscopy. Exposure to 2% sevoflurane for 6 h resulted in BBB ultrastructural abnormalities in the hippocampus of neonatal mice. Sugammadex alone without sevoflurane did not induce apoptosis. The coadministration of sugammadex with sevoflurane to neonatal mice caused a significant increase (150%) in neuroapoptosis in the brain compared with 2% sevoflurane. In neonatal anesthesia, sugammadex could influence neurotoxicity together with sevoflurane. Exposure to 2% sevoflurane for 6 h resulted in BBB ultrastructural abnormalities in the hippocampus of neonatal mice.

Optimal acquisition and modeling parameters for accurate assessment of low Ktrans blood-brain barrier permeability using dynamic contrast-enhanced MRI.

To determine optimal parameters for acquisition and processing of dynamic contrast-enhanced MRI (DCE-MRI) to detect small changes in near normal low blood-brain barrier (BBB) permeability. Using a contrast-to-noise ratio metric (K-CNR) for Ktrans precision and accuracy, the effects of kinetic model selection, scan duration, temporal resolution, signal drift, and length of baseline on the estimation of low permeability values was evaluated with simulations. The Patlak model was shown to give the highest K-CNR at low Ktrans . The Ktrans transition point, above which other models yielded superior results, was highly dependent on scan duration and tissue extravascular extracellular volume fraction (ve ). The highest K-CNR for low Ktrans was obtained when Patlak model analysis was combined with long scan times (10-30 min), modest temporal resolution (<60 s/image), and long baseline scans (1-4 min). Signal drift as low as 3% was shown to affect the accuracy of Ktrans estimation with Patlak analysis. DCE acquisition and modeling parameters are interdependent and should be optimized together for the tissue being imaged. Appropriately optimized protocols can detect even the subtlest changes in BBB integrity and may be used to probe the earliest changes in neurodegenerative diseases such as Alzheimer's disease and multiple sclerosis.

Vascular plasticity and cognition during normal aging and dementia.

Functional neurovascular changes reflecting alterations in brain function and cognition and/or originating primarily from abnormalities localized to the cerebrovascular system have been described in many neurological disorders and during normal brain aging. However, the relationship between vascular and neuronal dysfunction, and how they relate to each other and contribute to cognitive impairment and dementia due to Alzheimer’s disease (AD), vascular cognitive impairment and dementia (VCID), and/or other neurological disorders, still remains controversial1,2. An obvious place to look for neurovascular and cognitive changes is in the hippocampus, a region involved with learning and memory that is particularly susceptible to changes in oxygen and blood supply and is damaged early in AD. Using a variety of magnetic resonance imaging (MRI) techniques3,4 including cerebral blood volume (CBV)-fMRI with gadolinium contrast5, it was found that hypometabolism coupled with diminished CBV in the hippocampus is associated with cognitive impairment in the elderly and early stages of AD. Employing an advanced protocol and post-processing analysis of the CBV-fMRI maps in the hippocampus, a recent study interrogated whether functional changes in the dentate gyrus drive hippocampus-specific cognitive dysfunction in cognitively normal older adults who were enrolled in a randomized trial with cocoa flavanols, an ingredient in cocoa, red wine, berries and dark chocolate6. Interestingly, this recent study6 showed that high-flavanol dietary intake increases the CBV in the dentate gyrus and enhances performance on a modified version of the Benton Visual Retention Test (ModBent) that is dependent on pattern separation in the hippocampus, specifically localized to the dentate gyrus. These recent findings raise a possibility that during normal aging the human hippocampus retains significant vasculoplastic reserve that is likely mediated via enhanced angiogenesis and/or new blood vessel formation. The question persists, however, whether changes in basal blood flow, blood-brain barrier (BBB) permeability and/or brain activation that all can be studied by imaging neurovascular function in the living human brain with different techniques such as arterial spin labeling (ASL)-MRI, dynamic contrast-enhanced (DCE)-MRI7 and/or BOLD-fMRI, respectively, can also play a role in the observed adaptive cognition responses during normal aging (Figure 1). Additionally, major genetic risk factors such as apolipoprotein E4 allele for late onset AD, or presenilin 1 gene mutations for familial AD, as well as environmental factors and vascular risk factors might also affect formation of these adaptive responses. These questions warrant future investigations. Some other interesting and timely questions are when and whether cortical or subcortical brain regions or white matter connections become involved to cause cognitive impairment and/or accelerate progressive cognitive decline and hippocampal atrophy associated with dementia, which all can be studied in the living human brain by the diffusion tensor imaging (DTI)-MRI (Figure 1). Figure 1 Modern neuroimaging techniques may provide new insights into the vascular and neural plasticity of the hippocampus in aging and disease As CBV-fMRI is a neurovascular-dependent outcome measure of hippocampal function in the absence of brain activation, it is worth noting that increasingly recognized alterations in the neurovascular functions in many neurological disorders associated with cognitive impairment1,2 might potentially influence presently used fMRI measurements. It would be interesting to know, for example, how the CBV-fMRI findings relate to changes in BBB integrity that have been reported in AD and VCID1,2 and more recently during normal aging in the hippocampus that worsen with MCI, as suggested by a recent study7. Use of the DCE-MRI approach to determine regional BBB integrity7 and the effects of lifestyle modifiers such as flavanols, exercise and/or the role of vascular risk factors and their treatment during cognitively normal aging and aging associated with MCI, AD and/or VCID may help us better understand the emerging role of the cerebral vascular system in maintaining overall cognitive health. Future studies using multiple imaging biomarkers to access neurovascular function in relation to cognition and brain function (Figure 1), and combining imaging biomarkers with analysis of molecular cerebrospinal fluid biomarkers of the cell-specific injury within the neurovascular unit are needed to establish whether vascular dysfunction can precede neuronal dysfunction and cognitive impairment during normal aging, dementia due to AD and related disorders, or VCID, and ultimately how these changes are influenced by lifestyle, genetics and environment.

Striatal Blood–Brain Barrier Permeability in Parkinson'S Disease

In vivo studies have shown that blood-brain barrier (BBB) dysfunction is involved in the course of Parkinson's disease (PD). However, these have lacked either anatomic definition or the ability to recognize minute changes in BBB integrity. Here, using histologic markers of serum protein, iron, and erythrocyte extravasation, we have shown significantly increased permeability of the BBB in the postcommissural putamen of PD patients. The dense innervation of the striatum by PD-affected regions allows for exploitation of this permeability for therapeutic goals. These results are also discussed in the context of the retrograde trans-synaptic hypothesis of PD spread.

Longitudinal assessment of blood–brain barrier leakage during epileptogenesis in rats. A quantitative MRI study

The blood–brain barrier (BBB) plays an important role in the homeostasis of the brain. BBB dysfunction has been implicated in the pathophysiology of various neurological disorders, including epilepsy in which it may contribute to disease progression. Precise understanding of BBB dynamics during epileptogenesis may be of importance for the assessment of future therapies, including BBB leakage blocking-agents. Longitudinal changes in BBB integrity can be studied with in vivo magnetic resonance imaging (MRI) in combination with paramagnetic contrast agents. Although this approach has shown to be suitable to detect major BBB leakage during the acute phase in experimental epilepsy models, so far no studies have provided information on dynamics of the extent of BBB leakage towards later phases. Therefore a sensitive and quantitative approach was used in the present study, involving fast T1 mapping (dynamic approach) during a steady-state infusion of gadobutrol, as well as pre- and post-contrast T1-weighted MRI (post–pre approach). This was applied in an experimental epilepsy model in which previous MRI studies failed to detect BBB leakage during epileptogenesis.Adult male Sprague–Dawley rats were injected with kainic acid to induce status epilepticus (SE). MRI experiments were performed before SE (control) and during the acute (1day) and chronic epileptic phases (6weeks after SE). BBB leakage was quantified by fast T1 mapping (Look–Locker gradient echo MRI) with a time resolution of 48s from 5min before up to 45min after 20min step-down infusion of 0.2M gadobutrol. In addition, T1-weighted MRI was acquired before and 45min after infusion. MRI data were compared to post-mortem microscopic analysis using the BBB tracer fluorescein.Our MRI data showed BBB leakage, which was evident at 1day and 6weeks after SE in the hippocampus, entorhinal cortex, amygdala and piriform cortex. These findings were confirmed by microscopic analysis of fluorescein leakage. Furthermore, our MRI data revealed non-uniform BBB leakage throughout epileptogenesis. This study demonstrates BBB leakage in specific brain regions during epileptogenesis, which can be quantified using MRI. Therefore, MRI may be a valuable tool for experimental or clinical studies to elucidate the role of the BBB in epileptogenesis.

Aging-Related Changes in Blood-Brain Barrier Integrity and the Effect of Dietary Fat

Background: Disturbances in blood-brain barrier (BBB) integrity contribute to the onset and progression of neurodegenerative diseases including Alzheimer's disease (AD) and vascular dementia (VaD). Aging is positively associated with AD and VaD risk, but this may reflect comorbidities or the effects of other chronic modulators of vascular function such as diet. Objective: To explore putative synergistic effects of aging with diet, in this study genetically unmanipulated mice were maintained on diets enriched in saturated fatty acids (SFA) or cholesterol and compared to mice provided with low-fat (LF) feed formula. Methods: The functional integrity of the BBB was assessed following 3, 6 and 12 months of dietary intervention commenced at 6 weeks of age, by determining the brain parenchymal extravasation of immunoglobulin G (IgG). Results: Mice maintained on the SFA- or cholesterol-enriched diet showed significant parenchymal IgG abundance following 3 months of feeding, concomitant with diminished expression of the tight junction protein occludin. LF control mice had essentially no evidence of BBB disturbances. Six months of SFA feeding exacerbated the difference in IgG abundance compared to the LF mice. At 12 months of feeding, the control LF mice also had significant parenchymal IgG that was comparable to mice fed the SFA- or cholesterol-enriched diet for 3 months. However, there may have been an adaptation to the fat-enriched diets because SFA and cholesterol did not exacerbate IgG parenchymal accumulation beyond 6 months of feeding. Conclusion: Collectively, the study suggests that diets enriched in SFA or cholesterol accelerate the onset of BBB dysfunction that otherwise occurs with aging.

P3‐045: Effects of a high‐fat diet on the cerebrovasculature and neuroinflammation in an experimental model of Alzheimer's disease

Background:Western diets and mid-life obesity are considered risk factors for developing dementia. Experimentally, such diets increase ADlike pathology and/or behavioural deficits in transgenic mouse models of AD. We have shown that a high-fat diet increases memory deficits in male triple-transgenic (3xTgAD) mice, though the mechanisms underlying this effect are unknown. Several structural and functional cerebrovascular abnormalities are associated with AD, including impaired integrity of the blood brain barrier (BBB) and neurovascular inflammation. A common underlying feature of both obesity and AD is chronic inflammation. The aim of this project is to determine the molecular mechanisms underlying detrimental effects of a high-fat diet on AD, and to test the hypothesis that inflammatory driven changes in cerebrovascular function are crucial. Methods: Groups of male 3xTgAD and control (non-Tg) mice were maintained on a control diet or a high-fat diet for periods from 3to 16 months of age. Overt changes in BBB integrity (IgG), cerebrovascular endothelial activation (intracellular adhesion molecule; ICAM) and neuroinflammation (microglial activation, Iba1) were assessed by immunohistochemistry on brain sections. Brain homogenates from control fed 9-month-old female 3xTgAD and non-Tg mice were used to assess cerebrovascular activation/inflammation (ICAM and vascular adhesion molecule; VCAM) by ELISA. Results: No significant differences were observed in IgG staining in the brains of non-Tg and 3xTgAD male mice on either a control or high-fat diet at all ages tested. Increases in ICAM/VCAM protein expression were identified in the hippocampus of 9-month-old 3xTgAD female mice. However, no differences in the number of ICAM positive vessels between male Non-Tg and 3xTgAD mice on either a control or high-fat diet were identified by immunohistochemistry. Age-related increases in the number of activated microglia were observed in the hippocampus of 3xTgAD when compared to non-Tg control mice. High-fat feeding increased the number of activated microglia in the hippocampus of non-Tg mice but had no effect in 3xTgAD mice.Conclusions: These data suggest that a high-fat diet can induce neuroinflammation in the absence of AD-related pathology and that the mechanisms underlying the detrimental effects of a high-fat diet on behaviour in 3xTgAD mice remain to be resolved.

A Novel Positron Emission Tomography Imaging Protocol Identifies Seizure-Induced Regional Overactivity of P-Glycoprotein at the Blood-Brain Barrier

Approximately one-third of epilepsy patients are pharmacoresistant. Overexpression of P-glycoprotein and other multidrug transporters at the blood-brain barrier is thought to play an important role in drug-refractory epilepsy. Thus, quantification of regionally different P-glycoprotein activity in the brain in vivo is essential to identify P-glycoprotein overactivity as the relevant mechanism for drug resistance in an individual patient. Using the radiolabeled P-glycoprotein substrate (R)-[(11)C]verapamil and different doses of coadministered tariquidar, which is an inhibitor of P-glycoprotein, we evaluated whether small-animal positron emission tomography can quantify regional changes in transporter function in the rat brain at baseline and 48 h after a pilocarpine-induced status epilepticus. P-glycoprotein expression was additionally quantified by immunohistochemistry. To reveal putative seizure-induced changes in blood-brain barrier integrity, we performed gadolinium-enhanced magnetic resonance scans on a 7.0 tesla small-animal scanner. Before P-glycoprotein modulation, brain uptake of (R)-[(11)C]verapamil was low in all regions investigated in control and post-status epilepticus rats. After administration of 3 mg/kg tariquidar, which inhibits P-glycoprotein only partially, we observed increased regional differentiation in brain activity uptake in post-status epilepticus versus control rats, which diminished after maximal P-glycoprotein inhibition. Regional increases in the efflux rate constant k(2), but not in distribution volume V(T) or influx rate constant K(1), correlated significantly with increases in P-glycoprotein expression measured by immunohistochemistry. This imaging protocol proves to be suitable to detect seizure-induced regional changes in P-glycoprotein activity and is readily applicable to humans, with the aim to detect relevant mechanisms of pharmacoresistance in epilepsy in vivo.

Blood–brain barrier function in cerebral malaria and CNS infections in Vietnam

The intraerythrocytic parasite Plasmodium falciparum induces the life-threatening neurologic syndrome of cerebral malaria (CM) from within cerebral blood vessels, without entering the brain parenchyma. 1) To assess the use of CSF as an indicator of specific pathologic processes occurring in the brain during CM; 2) to compare this with other neurologic and infectious diseases to understand the distinct pathogenic features of CM; 3) to test the hypothesis that CM involves a specific functional breakdown of the blood-brain barrier (BBB). 1) Radial immunodiffusion assays to detect albumin and IgG in matched plasma and CSF samples as indicators of BBB integrity and intrathecal IgG production; and 2) ELISA for soluble intracellular adhesion molecule-1 and sE-selectin, the cytokines tumor necrosis factor-alpha and transforming growth factor-beta1, and the matrix metalloproteinase MMP-9, to detect cellular activation and inflammatory responses within the brain. Albumin and IgG indices implied only minimal degree of BBB breakdown in a few cases of CM, with most remaining within the normal range. In contrast, cryptococcal, tubercular, and acute bacterial meningitis produced detectable changes in the composition of the CSF and evidence of BBB breakdown. CM appears to involve only subtle functional changes in BBB integrity with minimal intraparenchymal inflammatory responses compared with other neurologic infections. This focuses attention on local events within and around the cerebral microvasculature in CM, rather than indicating widespread parenchymal disease.

Measurement of blood-brain barrier permeability with positron emission tomography and [68Ga]EDTA.

Positron emission tomography (PET) was employed to examine time-dependent changes in blood-brain barrier (BBB) permeability to [68Ga]ethylenediaminetetraacetate (EDTA) in the rhesus monkey, following reversible barrier opening by intracarotid infusion of a hypertonic mannitol solution. The PET technique, when combined with measurements of plasma radioactivity, provided a quantitative measure of the cerebrovascular permeability-area product (PA) at different times following mannitol infusion. Hypertonic mannitol treatment reversibly increased PA to [68Ga]EDTA more than 10-fold; much of the barrier effect was over by 10 min after mannitol treatment. The results show that PET can be used to measure transient changes in BBB integrity in specific brain regions, under in vivo, noninvasive conditions.