Alterations In Blood-brain Barrier Integrity Research Articles

Alterations in Blood-Brain Barrier Integrity and Lateral Ventricle Differ in Rats Exposed to Space Radiation and Social Isolation.

The proposed Mars missions will expose astronauts to long durations of social isolation (SI) and space radiation (SR). These stressors have been shown to alter the brain's macrostructure and microenvironment, including the blood-brain barrier (BBB). Breakdown of the BBB is linked to impaired executive functions and physical deficits, including sensorimotor and neurocognitive impairments. However, the precise mechanisms mediating these effects remain unknown. Additionally, the synergistic effects of combined exposure to SI and SR on the structural integrity of the BBB and brain remain unknown. We assessed the BBB integrity and morphology in the brains of male rats exposed to ground-based analogs of SI and SR. The rats exposed to SR had enlarged lateral ventricles and increased BBB damage associated with a loss of astrocytes and an increased number of leaky vessels. Many deficits observed in SR-treated animals were attenuated by dual exposure to SI (DFS). SI alone did not show BBB damage but did show differences in astrocyte morphology compared to the Controls. Thus, determining how single and combined inflight stressors modulate CNS structural integrity is crucial to fully understand the multiple pathways that could impact astronaut performance and health, including the alterations to the CNS structures and cell viability observed in this study.

Repetitive head trauma and apoE4 induce chronic cerebrovascular alterations that impair tau elimination from the brain

Repetitive mild traumatic brain injuries (r-mTBI) sustained in the military or contact sports have been associated with the accumulation of extracellular tau in the brain, which may contribute to the pathogenesis of neurodegenerative tauopathies. The expression of the apolipoprotein E4 (apoE4) isoform has been associated with higher levels of tau in the brain, and worse clinical outcomes after r-mTBI, though the influence of apoE genotype on extracellular tau dynamics in the brain is poorly understood. We recently demonstrated that extracellular tau can be eliminated across blood-brain barrier (BBB), which is progressively impaired following r-mTBI. The current studies investigated the influence of repetitive mild TBI (r-mTBI) and apoE genotype on the elimination of extracellular solutes from the brain. Following intracortical injection of biotin-labeled tau into humanized apoE-Tr mice, the levels of exogenous tau residing in the brain of apoE4 mice were elevated compared to other isoforms, indicating reduced tau elimination. Additionally, we found exposure to r-mTBI increased tau residence in apoE2 mice, similar to our observations in E2FAD animals. Each of these findings may be the result of diminished tau efflux via LRP1 at the BBB, as LRP1 inhibition significantly reduced tau uptake in endothelial cells and decreased tau transit across an in vitro model of the BBB (basolateral-to-apical). Notably, we showed that injury and apoE status, (particularly apoE4) resulted in chronic alterations in BBB integrity, pericyte coverage, and AQP4 polarization. These aberrations coincided with an atypical reactive astrocytic gene signature indicative of diminished CSF-ISF exchange. Our work found that CSF movement was reduced in the chronic phase following r-mTBI (>18 months post injury) across all apoE genotypes. In summary, we show that apoE genotype strongly influences cerebrovascular homeostasis, which can lead to age-dependent deficiencies in the elimination of toxic proteins from the brain, like tau, particularly in the aftermath of head trauma.

Abstract 279: Transient opening of the blood brain barrier by Tumor Treating Fields (TTFields)

Abstract Introduction Alternating electric fields of intermediate frequency and low intensity, known as Tumor Treating Fields (TTFields), are an effective and clinically approved approach for treatment of glioblastoma (GBM). The optimal frequency for treatment of glioma cells based on the cytotoxic response is at 200 kHz. Combination of TTFields with chemotherapy appears to be synergistic with further increase in overall survival of patients with GBM, beyond that with chemotherapy alone. The blood brain barrier (BBB) limits delivery of a majority of drugs to the brain thus limiting treatment options for GBM patients. Recent in vitro studies suggest that TTFields applied at 100 kHz can disturb the BBB. In this study, we investigated the potential use of TTFields to transiently disturb the BBB in animal models. Methods BBB permeation was tested in healthy rats subsequently to 100 kHz TTFields or sham (heat) application to the rat head. BBB permeability was analyzed by several staining agents: (1) Evans Blue (EB) that was quantified at 610 nm in brain homogenates; (2) 4 kDa TRITC-dextran (TD) that was quantified based on fluorescence intensity in brain cryosections; and (3) the MRI contrast agent Gd-DTPA. Accumulation and clearance of Gd-DTPA were tracked by serial dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). In addition, brain sections were stained for claudin-5, occludin, PECAM-1 and immunoglobulin G (IgG). BBB permeation induced by TTFields was further evaluated in rats orthotopically bearing F98 glioma cells and treated with TTFields at 100 kHz in combination with the chemotherapeutic drug paclitaxel (PTX) for a duration of 72 h. Tumor cell proliferation was assessed by Ki67 staining and the tumor volume was measured by T2 weighted MRI. Results BBB permeation of EB and TD staining agents was observed in the brains of healthy rats after TTFields application. Moreover, brain cryosections displayed delocalization of claudin-5 and occludin, but not of PECAM-1. Accumulation of IgG in the brain parenchyma was also noted. Confirming these observations, DCE-MRI post-TTFields treatment showed accumulation of Gd in the brain. Return to normal BBB integrity was detected 96 h after TTFields treatment cessation, indicating the effect was transient and reversible. In GBM-induced rats, the combination of PTX (a drug which normally does not cross the BBB) with TTFields significantly decreased tumor cell proliferation and tumor volume compared to animals treated with TTFields alone, sham alone, or sham combined with PTX. Conclusions Administration of 100 kHz TTFields to the brain of rats led to transient alterations in BBB integrity and permeability, allowing increased uptake of combination chemotherapy. These data indicate that TTFields treatment may be a feasible, novel clinical strategy for transient opening of the BBB to allow for enhanced and more effective delivery of permeable and non-permeable anticancer drugs to the brain. Citation Format: Catherine Tempel Brami, Ellaine Salvador, Almuth F. Kessler, Malgorzata Burek, Tali Voloshin, Moshe Giladi, Ralf-Ingo Ernestus, Mario Löhr, Carola Förster, Carsten Hagemann. Transient opening of the blood brain barrier by Tumor Treating Fields (TTFields) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 279.

Ca2+ homeostasis in brain microvascular endothelial cells.

Blood brain barrier (BBB) is formed by the brain microvascular endothelial cells (BMVECs) lining the wall of brain capillaries. Its integrity is regulated by multiple mechanisms, including up/downregulation of tight junction proteins or adhesion molecules, altered Ca2+ homeostasis, remodeling of cytoskeleton, that are confined at the level of BMVECs. Beside the contribution of BMVECs to BBB permeability changes, other cells, such as pericytes, astrocytes, microglia, leukocytes or neurons, etc. are also exerting direct or indirect modulatory effects on BBB. Alterations in BBB integrity play a key role in multiple brain pathologies, including neurological (e.g. epilepsy) and neurodegenerative disorders (e.g. Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis etc.). In this review, the principal Ca2+ signaling pathways in brain microvascular endothelial cells are discussed and their contribution to BBB integrity is emphasized. Improving the knowledge of Ca2+ homeostasis alterations in BMVECa is fundamental to identify new possible drug targets that diminish/prevent BBB permeabilization in neurological and neurodegenerative disorders.

Abstract 6251: Blood brain barrier opening by TTFields: a future CNS drug delivery strategy

Abstract Introduction: Although a number of effective drugs are available to treat central nervous system (CNS) disorders, their ability to breach the tight regulation of the blood brain barrier (BBB) still remains a major challenge. Recently, the use of tumor treating fields (TTFields) has become an effective treatment approach for glioblastoma. Furthermore, its combination with chemotherapy significantly improved overall patient survival. Nonetheless, how TTFields could affect the BBB has not yet been studied. Our recent findings exhibit the potential of TTFields administration to open up the BBB in vitro with an optimal frequency of 100 kHz. Consequently, in this study, we therefore aimed to validate our data in vivo. Experimental procedures: Subsequent to 100 kHz TTFields or heat treatment for 72 h, rats were i.v. injected with Evan´s Blue (EB). Next, they were sacrificed to extract and quantify EB from the brain. In the same manner, rats were injected with TRITC-dextran (TD), after which permeation was visualized in sectioned brains. Cryosections of rat brains were also prepared post-TTFields treatment. These were stained for intercellular junction proteins claudin-5, occludin and PECAM-1 as well as immunoglobulin G (IgG) to assess vessel structure. Finally, serial dynamic contrast-enhanced (DCE) MRI with gadolinium (Gd) contrast agent was performed before and after TTFields administration. Results: Permeation of both EB and TD was observed in the brain after TTFields application. Moreover, brain cryosections displayed claudin-5 and occludin delocalization but not PECAM-1. Accumulation of IgG in the brain parenchyma was also noted. Confirming these observations, increased Gd in the brain was shown by DCE-MRI post TTFields treatment. A reversion to normal conditions was, however, detected 96 h after end of treatment demonstrated by no difference in contrast enhancement between control and TTFields-treated rats. Conclusions: Administration of 100 kHz TTFields in rats led to alterations in BBB integrity and permeability, which signal its opening. The subsequent recovery of the BBB at the end of treatment demonstrates transient effects, hence presenting TTFields as a possible novel clinical strategy to open the BBB for enhanced and more effective drug delivery strategy for CNS disorders. Citation Format: Ellaine Salvador, Almuth F. Kessler, Julia Hörmann, Malgorzata Burek, Catherine T. Brami, Tali V. Sela, Moshe Giladi, Ralf-Ingo Ernestus, Mario Löhr, Carola Förster, Carsten Hagemann. Blood brain barrier opening by TTFields: a future CNS drug delivery strategy [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6251.

The role of the lectin-like oxLDL receptor (LOX-1) in traffic-generated air pollution exposure-mediated alteration of the brain microvasculature in Apolipoprotein (Apo) E knockout mice

Recent studies have shown a strong correlation between air pollution-exposure and detrimental outcomes in the central nervous system, including alterations in blood brain barrier (BBB) integrity, neuroinflammation, and neurodegeneration. However, the mechanisms mediating these pathologies have not yet been fully elucidated. We have previously reported that exposure to traffic-generated air pollution results in increased circulating oxidized low-density lipoprotein (oxLDL), associated with alterations in BBB integrity, in atherosclerotic Apolipoprotein E null (ApoE−/−) mice. Thus, we investigated the role of the lectin-like oxLDL receptor (LOX)-1 in mediating these deleterious effects in ApoE−/− mice exposed to a mixture of gasoline and diesel engine exhaust (MVE: 100 PM µg/m3) for 6 h/d, 7d/week, for 30 d by inhalation. Concurrent with exposures, a subset of mice were treated with neutralizing antibodies to LOX-1 (LOX-1 Ab) i.p., or IgG (control) i.p., every other day during exposures. Resulting brain microvascular integrity, tight junction (TJ) protein expression, matrix metalloproteinase (MMP)-9/-2 activity, ROS, and markers of cellular adhesion and monocyte/macrophage sequestration were assessed. MVE-exposure resulted in decreased BBB integrity and alterations in microvascular TJ protein expression, associated with increased LOX-1 expression, MMP-9/-2 activities, and lipid peroxidation, each of which was attenuated with LOX-1 Ab treatment. Furthermore, MVE-exposure induced cerebral microvascular ROS and adhesion molecules, expression of which was not normalized through LOX-1 Ab-treatment. Such findings suggest that alterations in brain microvascular structure and integrity observed with MVE-exposure may be mediated, at least in part, via LOX-1 signaling.

The effects of superoxide dismutase mimetic MnTMPyP on the altered blood–brain barrier integrity in experimental preeclampsia with or without seizures in rats

We investigated the effects of a cell-permeable superoxide dismutase mimetic, manganese(III) tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP) on blood–brain barrier (BBB) integrity following pentylenetetrazole (PTZ)-induced seizures in experimental preeclampsia symptoms induced by N(omega)-nitro-l-arginine methyl ester (l-NAME) in pregnant rats. To show the functional and morphological alterations in BBB integrity, quantitative analysis of sodium fluorescein (NaFlu) extravasation, immunohistochemistry and electron microscopic assessment of horseradish peroxidase (HRP) permeability were performed. Varying degrees of proteinuria were seen and arterial blood pressure increased in l-NAME-treated pregnant rats (p<0.01). MnTMPyP pretreatment and convulsive PTZ challenge significantly decreased the immunoreactivity of occludin in hippocampal capillaries in l-NAME-treated pregnant rats (p<0.01). BBB permeability to NaFlu significantly increased in pregnant rats treated with l-NAME plus PTZ (p<0.01), but MnTMPyP pretreatment did not significantly decrease NaFlu penetration into the brain parenchyma in these animals. Ultrastructurally, frequent vesicles containing HRP reaction products were observed in the capillary endothelial cells in the cerebral cortex and hippocampus of pregnant rats treated with l-NAME and l-NAME plus PTZ with the abundance being more in the latter group. MnTMPyP pretreatment caused a marked reduction in the frequency of HRP reaction product containing vesicles in both experimental settings. In conclusion, the results of the present study provide evidence that MnTMPyP plays an important role in limiting the enhanced vesicle-mediated transcellular transport in BBB endothelium in a rat model of preeclampsia and the differences in the way of transports of NaFlu and HRP might be responsible for the different effects of MnTMPyP on the BBB permeability to these two tracers.

Topiramate reduces blood–brain barrier disruption and inhibits seizure activity in hyperthermia-induced seizures in rats with cortical dysplasia

We investigated the effects of topiramate (TPM), a novel broad spectrum anticonvulsant, on seizure severity, survival rate and blood–brain barrier (BBB) integrity during hyperthermic seizures in rats with cortical dysplasia (CD). Offsprings of irradiated mothers were used in this study. To show the functional and morphological alterations in BBB integrity, quantitative analysis of Evans blue (EB) extravasation, immunohistochemistry and electron microscopic assessment of horseradish peroxidase (HRP) permeability were performed. Rats with CD exposed to hyperthermia exhibited seizures with mean Racine's scores of 3.92±1.2. Among the rats with CD pretreated with TPM, 21 of 24 rats showed no sign of seizure activity upon exposure to hyperthermia (p<0.01). The immunoreactivity of occludin, a tight junction protein, remained essentially unaltered in capillaries of hippocampus in all groups. In animals with CD exposed to hyperthermia, the significantly increased p-glycoprotein immunoreactivity in hippocampus (p<0.01) was slightly decreased by TPM pretreatment. Hyperthermic seizures increased BBB permeability to EB in animals with CD, but TPM pretreatment decreased the penetration of the tracer into the brain in these animals (p<0.01). Ultrastructurally frequent vesicles containing HRP reaction products were observed in capillary endothelial cells in cerebral cortex and hippocampus of rats with CD subjected to hyperthermia-induced seizures, and TPM pretreatment prevented the development of HRP reaction products in these animals. The results of this study suggest that TPM inhibits seizure activity and maintains BBB integrity in the course of febrile seizures in the setting of CD.

Vascular Changes in Rat Hippocampus following a High Saturated Fat and Cholesterol Diet

The long-term effects of a diet rich in saturated fat and cholesterol on the hippocampus were evaluated in this study. It has previously been shown that this type of diet is detrimental to health, particularly affecting peripheral organs such as the heart and liver. However, effects on the brain have not been fully evaluated. This study focused on the hippocampus, a brain region instrumental for learning and memory and vulnerable to ischemic damage. Reduced blood-brain barrier (BBB) integrity and increased microgliosis were observed in the hippocampus of rats fed a high-saturated-fat and cholesterol (HFHC) diet for 6 months. Interestingly, an increase in hippocampal protein levels of occludin, a tight junction protein, was found in HFHC-treated rats as well. Further investigation revealed decreased expression of the occludin protein in blood vessels and increased expression in the dentate gyrus hilar neurons and mossy fibers of the hippocampal cornus ammonis 3 in HFHC-treated rats. Our results show alterations in BBB integrity and expression of tight junction proteins after long-term exposure to HFHC diet in rats. These findings may suggest a biologic mechanism for previously observed behavioral deficits occurring in rats fed this diet.

Do ATP-Binding Cassette Transporters Cause Pharmacoresistance in Epilepsy? Problems and Approaches in Determining which Antiepileptic Drugs are Affected

Resistance to multiple antiepileptic drugs (AEDs) is a common problem in epilepsy, affecting at least 30% of patients. One prominent hypothesis to explain this resistance suggests an inadequate penetration or excess efflux of AEDs across the blood - brain barrier (BBB) as a result of overexpressed efflux transporters such as P-glycoprotein (Pgp), the encoded product of the multidrug resistance- 1 (MDR1, ABCB1) gene. Pgp and MDR1 are markedly increased in epileptogenic brain tissue of patients with AED-resistant partial epilepsy and following seizures in rodent models of partial epilepsy. In rodent models, AED-resistant rats exhibit higher Pgp levels than responsive animals; increased Pgp expression is associated with lower brain levels of AEDs; and, most importantly, co-administration of Pgp inhibitors reverses AED resistance. Thus, it is reasonable to conclude that Pgp plays a significant role in mediating resistance to AEDs in rodent models of epilepsy - however, whether this phenomenon extends to at least some human refractory epilepsy remains unclear, particularly because it is still a matter of debate which AEDs, if any, are transported by human Pgp. The difficulty in determining which AEDs are substrates of human Pgp is mainly a consequence of the fact that AEDs are highly permeable compounds, which are not easily identified as Pgp substrates in in vitro models of the BBB, such as monolayer (Transwell(®)) efflux assays. By using a modified assay (concentration equilibrium transport assay; CETA), which minimizes the influence of high transcellular permeability, two groups have recently demonstrated that several major AEDs are transported by human Pgp. Importantly, it was demonstrated in these studies that Pgp-mediated transport highly depends on the AED concentration and may not be identified if concentrations below or above the therapeutic range are used. In addition to the efflux transporters, seizure-induced alterations in BBB integrity and activity of drug metabolizing enzymes (CYPs) affect the brain uptake of AEDs. For translating these findings to the clinical arena, in vivo imaging studies using positron emission tomography (PET) with (11)C-labelled AEDs in epileptic patients are under way.

Impact of seizure activity on free extracellular phenytoin concentrations in amygdala-kindled rats

Access of antiepileptic drugs (AEDs) to the epileptic focus region is considered to be influenced by seizure-associated changes in blood–brain barrier (BBB) function and blood flow. Enhanced leakiness of the BBB has been reported as a consequence of seizure activity, and this is controversially discussed to either favor accumulation of AEDs in epileptic tissue or to limit free extracellular concentrations of AEDs due to enhanced protein extravasation. On the other hand, multidrug transporter overexpression has been described following seizure activity, which can limit brain penetration of AEDs in brain regions involved in seizure generation and spread. Aim of the present study was to determine, how these complex alterations at the BBB influence penetration of a standard AED to the site of seizure initiation. Microdialysis experiments were performed in amygdala-kindled rats and in electrode-implanted, non-kindled rats with the microdialysis probe located directly adjacent to the stimulation-recording depth electrode. Penetration of the AED phenytoin to the extracellular fluid in the focus region was investigated at different time points in relation to seizure activity elicited in kindled rats. Integrity of the BBB was determined by Evans blue. Access of phenytoin to the amygdala proved to be comparable in non-kindled, electrode-implanted control rats and in kindled rats 2 h or fourteen days following a single generalized seizure. When a single generalized seizure was elicited 10 min following phenytoin administration, average phenytoin brain dialysate levels were significantly lower (up to 45%) than those of control animals. During a self-sustained status epilepticus, phenytoin access to the site of seizure initiation tended to be lower in the early phase following drug administration, but reached control level 2 h later. The data clearly demonstrate that seizure-induced alterations in BBB integrity and function do not increase extracellular brain levels of phenytoin in affected brain regions, but rather tend to decrease the free concentration of phenytoin in the extracellular compartment.

Human Immunodeficiency Virus Infection of Human Astrocytes Disrupts Blood-Brain Barrier Integrity by a Gap Junction-Dependent Mechanism

HIV infection of the CNS is an early event after primary infection, resulting in neurological complications in a significant number of individuals despite antiretroviral therapy (ART). The main cells infected with HIV within the CNS are macrophages/microglia and a small fraction of astrocytes. The role of these few infected astrocytes in the pathogenesis of neuroAIDS has not been examined extensively. Here, we demonstrate that few HIV-infected astrocytes (4.7 ± 2.8% in vitro and 8.2 ± 3.9% in vivo) compromise blood-brain barrier (BBB) integrity. This BBB disruption is due to endothelial apoptosis, misguided astrocyte end feet, and dysregulation of lipoxygenase/cyclooxygenase, BK(Ca) channels, and ATP receptor activation within astrocytes. All of these alterations in BBB integrity induced by a few HIV-infected astrocytes were gap junction dependent, as blocking these channels protected the BBB from HIV-infected astrocyte-mediated compromise. We also demonstrated apoptosis in vivo of BBB cells in contact with infected astrocytes using brain tissue sections from simian immunodeficiency virus-infected macaques as a model of neuroAIDS, suggesting an important role for these few infected astrocytes in the CNS damage seen with HIV infection. Our findings describe a novel mechanism of bystander BBB toxicity mediated by low numbers of HIV-infected astrocytes and amplified by gap junctions. This mechanism of toxicity contributes to understanding how CNS damage is spread even in the current ART era and how minimal or controlled HIV infection still results in cognitive impairment in a large population of infected individuals.

Effects of levetiracetam on blood-brain barrier disturbances following hyperthermia-induced seizures in rats with cortical dysplasia

Aims The mechanisms underlying the changes in blood-brain barrier (BBB) integrity and the generation of seizures in childhood associated with preexisting brain lesions like cortical dysplasia (CD) are poorly understood. We investigated the effects of levetiracetam (LEV) on BBB integrity and the survival during hyperthermic seizures in rats with CD. Main methods Pregnant rats were exposed to 145 cGy of gamma-irradiation on embryonic day 17. On postnatal day 28, hyperthermia-induced seizures were evoked in offspring with CD. To show the functional and morphological alterations in BBB integrity, quantitative analysis of sodium fluorescein (NaFlu) extravasation, immunohistochemistry and electron microscopy were performed. Key findings Seizure scores and mortality rates were decreased by LEV during hyperthermia-induced seizures in rats with CD (P < 0.01). Increased NaFlu extravasation into brain by hyperthermia-induced seizures in animals with CD was decreased by LEV (P < 0.01). While glial fibrillary acidic protein (GFAP) immunoreactivity slightly increased in brain sections of animals with CD during hyperthermia-induced seizures, LEV led to GFAP immunoreactivity comparable to that of controls. Decreased occludin immunoreactivity and expression in CD plus hyperthermia-induced seizures was increased by LEV. Opening of tight junctions and abundance of pinocytotic vesicles representing ultrastructural evidences of BBB impairment and severe perivascular edema were observed in animals with CD exposed to hyperthermia-induced seizures and LEV treatment led to the attenuation of these findings. Significance These results indicate that LEV may present a novel approach for the protection of the BBB besides its antiepileptic impact on hyperthermic seizures in the setting of CD.

Nociceptive inhibition prevents inflammatory pain induced changes in the blood–brain barrier

Previous studies by our group have shown that peripheral inflammatory insult, using the λ-carrageenan inflammatory pain (CIP) model, induced alterations in the molecular and functional properties of the blood–brain barrier (BBB). The question remained whether these changes were mediated via an inflammatory and/or neuronal mechanism. In this study, we investigated the involvement of neuronal input from pain activity on alterations in BBB integrity by peripheral inhibition of nociceptive input. A perineural injection of 0.75% bupivacaine into the right hind leg prior to CIP was used for peripheral nerve block. Upon nerve block, there was a significant decrease in thermal allodynia induced by CIP, but no effect on edema formation 1 h post-CIP. BBB permeability was increased 1 h post-CIP treatment as determined by in situ brain perfusion of [ 14C] sucrose; bupivacaine nerve block of CIP caused an attenuation of [ 14C] sucrose permeability, back to saline control levels. Paralleling the changes in [ 14C] sucrose permeability, we also report increased expression of three tight junction (TJ) proteins, zonula occluden-1 (ZO-1), occludin and claudin-5 with CIP. Upon bupivacaine nerve block, changes in expression were prevented. These data show that the λ-carrageenan-induced changes in [ 14C] sucrose permeability and protein expression of ZO-1, occludin and claudin-5 are prevented with inhibition of nociceptive input. Therefore, we suggest that nociceptive signaling is in part responsible for the alteration in BBB integrity under CIP.

Permeability of the blood-brain barrier to albumin and insulin in the young and aged SAMP8 mouse.

The decrease in the insulin cerebrospinal fluid/serum ratio seen in Alzheimer's disease has been suggested as a mechanism by which brain glucose utilization could be perturbed. Insulin is transported across the blood-brain barrier (BBB) by a system that is altered by pathophysiological events. We used SAMP8 mice, a strain that by 8-12 months of age develops severe deficits in learning and memory, to determine whether the insulin transporter or BBB integrity was altered with aging. BBB integrity was measured by injecting radioactive albumin intravenously, washing out the vascular space up to 17 hours later, and measuring brain/serum ratios. This very sensitive method found no increase in the permeability of the BBB to albumin in young and aged SAMP8 mice. This compares with previous studies in humans with Alzheimer's disease and in other colonies of SAMP8 mice that have found evidence for BBB disruption. For radioactively labeled insulin, we used multiple-time regression analysis to measure both the unidirectional influx rate (Ki) and the reversible binding to brain endothelium (Vi). A non-significant decrease in the transport rate for whole brain occurred in aged SAMP8 mice. Ki and Vi values significantly varied among brain regions and the Ki for the thalamus and the Vi for the cerebellum and thalamus were higher in aged mice. We conclude that alterations in BBB integrity or the activity of the BBB insulin transporter do not underlie the deficits in learning and memory seen in the aged SAMP8 mouse.

Blood-Brain Barrier Tight Junction Disruption in Human Immunodeficiency Virus-1 Encephalitis

The blood-brain barrier (BBB) plays a critical role in regulating cell trafficking through the central nervous system (CNS) due to several unique anatomical features, including the presence of interendothelial tight junctions that form impermeable seals between the cells. Previous studies have demonstrated BBB perturbations during human immunodeficiency virus encephalitis (HIVE); however, the basis of these permeability changes and its relationship to infiltration of human immunodeficiency virus type 1 (HIV-1)-infected monocytes, a critical event in the pathogenesis of the disease, remains unclear. In this study, we examined CNS tissue from HIV-1-seronegative patients and HIV-1-infected patients, both with and without encephalitis, for alterations in BBB integrity via immunohistochemical analysis of the tight junction membrane proteins, occludin and zonula occludens-1 (ZO-1). Significant tight junction disruption (P < 0.001), as demonstrated by fragmentation or absence of immunoreactivity for occludin and ZO-1, was observed within vessels from subcortical white matter, basal ganglia, and, to a lesser extent, cortical gray matter in patients who died with HIVE. These alterations were also associated with accumulation of activated, HIV-1-infected brain macrophages, fibrinogen leakage, and marked astrocytosis. In contrast, no significant changes (P > 0.05) were observed in cerebellar tissue from patients with HIVE compared to HIV-seronegative patients or HIV-1-infected patients without encephalitis. Our findings demonstrate that tight junction disruption is a key feature of HIVE that occurs in regions of histopathological alterations in association with perivascular accumulation of activated HIV-1-infected macrophages, serum protein extravasation, and marked astrocytosis. We propose that disruption of this key BBB structure serves as the main route of HIV-1-infected monocyte entry into the CNS.