Structural alterations of tight junctions are associated with loss of polarity in stroke-prone spontaneously hypertensive rat blood-brain barrier endothelial cells

Exploring the neuroprotective role of physical activity in cerebral small vessel disease

Cerebral small vessel disease (cSVD) is a common neurological finding characterized by abnormalities of the small blood vessels in the brain. Previous research has established a strong connection between cSVD and stroke, as well as neurodegenerative disorders, notably Alzheimer's disease (AD) and other dementias. As the search for effective interventions continues, physical activity (PA) has emerged as a potential preventative and therapeutic avenue. This review synthesizes the human and animal literature on the influence of PA on cSVD, highlighting the importance of determining optimal exercise protocols, considering aspects such as intensity, duration, timing, and exercise type. Furthermore, the necessity of widening the age bracket in research samples is discussed, ensuring a holistic understanding of the interventions across varying pathological stages of the disease. The review also suggests the potential of exploring diverse biomarkers and risk profiles associated with clinically significant outcomes. Moreover, we review findings demonstrating the beneficial effects of PA in various rodent models of cSVD, which have uncovered numerous mechanisms of neuroprotection, including increases in neuroplasticity and integrity of the vasculature and white matter; decreases in inflammation, oxidative stress, and mitochondrial dysfunction; and alterations in amyloid processing and neurotransmitter signaling. In conclusion, this review highlights the potential of physical activity as a preventive strategy for addressing cSVD, offering insights into the need for refining exercise parameters, diversifying research populations, and exploring novel biomarkers, while shedding light on the intricate mechanisms through which exercise confers neuroprotection in both humans and animal models.

Post-Ischemic Permeability of the Blood-Brain Barrier to Amyloid and Platelets as a Factor in the Maturation of Alzheimer's Disease-Type Brain Neurodegeneration

The aim of this review is to present evidence of the impact of ischemic changes in the blood-brain barrier on the maturation of post-ischemic brain neurodegeneration with features of Alzheimer's disease. Understanding the processes involved in the permeability of the post-ischemic blood-brain barrier during recirculation will provide clinically relevant knowledge regarding the neuropathological changes that ultimately lead to dementia of the Alzheimer's disease type. In this review, we try to distinguish between primary and secondary neuropathological processes during and after ischemia. Therefore, we can observe two hit stages that contribute to Alzheimer's disease development. The onset of ischemic brain pathology includes primary ischemic neuronal damage and death followed by the ischemic injury of the blood-brain barrier with serum leakage of amyloid into the brain tissue, leading to increased ischemic neuronal susceptibility to amyloid neurotoxicity, culminating in the formation of amyloid plaques and ending in full-blown dementia of the Alzheimer's disease type.

The Blood-Brain Barrier, an Evolving Concept Based on Technological Advances and Cell-Cell Communications

The construction of the blood–brain barrier (BBB), which is a natural barrier for maintaining brain homeostasis, is the result of a meticulous organisation in space and time of cell–cell communication processes between the endothelial cells that carry the BBB phenotype, the brain pericytes, the glial cells (mainly the astrocytes), and the neurons. The importance of these communications for the establishment, maturation and maintenance of this unique phenotype had already been suggested in the pioneering work to identify and demonstrate the BBB. As for the history of the BBB, the evolution of analytical techniques has allowed knowledge to evolve on the cell–cell communication pathways involved, as well as on the role played by the cells constituting the neurovascular unit in the maintenance of the BBB phenotype, and more particularly the brain pericytes. This review summarises the key points of the history of the BBB, from its origin to the current knowledge of its physiology, as well as the cell–cell communication pathways identified so far during its development, maintenance, and pathophysiological alteration.

Participation of Amyloid and Tau Protein in Post-Ischemic Neurodegeneration of the Hippocampus of a Nature Identical to Alzheimer's Disease

Recent evidence suggests that amyloid and tau protein are of vital importance in post-ischemic death of CA1 pyramidal neurons of the hippocampus. In this review, we summarize protein alterations associated with Alzheimer's disease and their gene expression (amyloid protein precursor and tau protein) after cerebral ischemia, as well as their roles in post-ischemic hippocampus neurodegeneration. In recent years, multiple studies aimed to elucidate the post-ischemic processes in the development of hippocampus neurodegeneration. Their findings have revealed the dysregulation of genes for amyloid protein precursor, β-secretase, presenilin 1 and 2, tau protein, autophagy, mitophagy, and apoptosis identical in nature to Alzheimer's disease. Herein, we present the latest data showing that amyloid and tau protein associated with Alzheimer's disease and their genes play a key role in post-ischemic neurodegeneration of the hippocampus with subsequent development of dementia. Therefore, understanding the underlying process for the development of post-ischemic CA1 area neurodegeneration in the hippocampus in conjunction with Alzheimer's disease-related proteins and genes will provide the most important therapeutic development goals to date.

Angiogenesis and Blood-Brain Barrier Permeability in Vascular Remodeling after Stroke

Angiogenesis, the growth of new blood vessels, is a natural defense mechanism helping to restore oxygen and nutrient supply to the affected brain tissue following an ischemic stroke. By stimulating vessel growth, angiogenesis may stabilize brain perfusion, thereby promoting neuronal survival, brain plasticity, and neurologic recovery. However, therapeutic angiogenesis after stroke faces challenges: new angiogenesis-induced vessels have a higher than normal permeability, and treatment to promote angiogenesis may exacerbate outcomes in stroke patients. The development of therapies requires elucidation of the precise cellular and molecular basis of the disease. Microenvironment homeostasis of the central nervous system is essential for its normal function and is maintained by the blood-brain barrier (BBB). Tight junction proteins (TJP) form the tight junction (TJ) between vascular endothelial cells (ECs) and play a key role in regulating the BBB permeability. We demonstrated that after stroke, new angiogenesis-induced vessels in peri-infarct areas have abnormally high BBB permeability due to a lack of major TJPs in ECs. Therefore, promoting TJ formation and BBB integrity in the new vessels coupled with speedy angiogenesis will provide a promising and safer treatment strategy for improving recovery from stroke. Pericyte is a central neurovascular unite component in vascular barriergenesis and are vital to BBB integrity. We found that pericytes also play a key role in stroke-induced angiogenesis and TJ formation in the newly formed vessels. Based on these findings, in this article, we focus on regulation aspects of the BBB functions and describe cellular and molecular special features of TJ formation with an emphasis on role of pericytes in BBB integrity during angiogenesis after stroke.

A blood-brain barrier overview on structure, function, impairment, and biomarkers of integrity

The blood–brain barrier is playing a critical role in controlling the influx and efflux of biological substances essential for the brain’s metabolic activity as well as neuronal function. Thus, the functional and structural integrity of the BBB is pivotal to maintain the homeostasis of the brain microenvironment. The different cells and structures contributing to developing this barrier are summarized along with the different functions that BBB plays at the brain–blood interface. We also explained the role of shear stress in maintaining BBB integrity. Furthermore, we elaborated on the clinical aspects that correlate between BBB disruption and different neurological and pathological conditions. Finally, we discussed several biomarkers that can help to assess the BBB permeability and integrity in-vitro or in-vivo and briefly explain their advantages and disadvantages.

Defective Function of the Blood-Brain Barrier in a Stroke-Prone Spontaneously Hypertensive Rat: Evaluation in an In Vitro Cell Culture Model

The blood-brain barrier (BBB) comprises three cell types: brain capillary endothelial cells (BECs), astrocytes, and pericytes. Abnormal interaction among these cells may induce BBB dysfunction and lead to cerebrovascular diseases. The stroke-prone spontaneously hypertensive rat (SHRSP) harbors a defective BBB, so we designed the present study to examine the role of these three cell types in a functional disorder of the BBB in SHRSP in order to elucidate the role of these cells in the BBB more generally. To this end, we employed a unique in vitro model of BBB, in which various combinations of the cells could be tested. The three types of cells were prepared from both SHRSPs and Wistar Kyoto rats (WKYs). They were then co-cultured in various combinations to construct in vitro BBB models. The barrier function of the models was estimated by measuring transendothelial electrical resistance and the permeability of the endothelial monolayer to sodium fluorescein. The in vitro models revealed that (1) BECs from SHRSPs had an inherent lower barrier function, (2) astrocytes of SHRSPs had an impaired ability to induce barrier function in BECs, although (3) both pericytes and astrocytes of SHRSPs and WKYs could potentiate the barrier function of BECs under co-culture conditions. Furthermore, we found that claudin-5 expression was consistently lower in models that used BECs and/or SHRSP astrocytes. These results suggested that defective interaction among BBB cells-especially BECs and astrocytes-was responsible for a functional disorder of the BBB in SHRSPs.

Blood-brain barrier dysfunction: the undervalued frontier of hypertension

The blood-brain barrier (BBB) constitutes the complex anatomic and physiologic interface between the intravascular compartment and the central nervous system, and its integrity is paramount for the maintenance of the very sensitive homeostasis of the central nervous system. Arterial hypertension is a leading cause of morbidity and mortality. The BBB has been shown to be disrupted in essential hypertension. BBB integrity is important for central autonomic control and this may be implicated in the pathophysiology of hypertension. On the other hand, evidence from experimental studies indicates that BBB disruption can be present in both hypertensive disease and dementia syndromes, suggesting a possibly key position of loss of BBB integrity in the pathophysiological pathways linking arterial hypertension with cognitive decline. Although much still remains to be elucidated with respect to the exact underlying mechanisms, the discovery of novel pathological pathways has changed our understanding of adult dementia and central nervous system disease overall, pointing out-in parallel-new potential therapeutic targets. The aim of this review is to summarize current scientific knowledge relevant to the pathophysiologic pathways that are involved in the disruption of the BBB function and potentially mediate hypertension-induced cognitive impairment. In parallel, we underline the differential cognition-preserving effect of several antihypertensive agents of similar blood pressure-lowering capacity, highlighting the presence of previously under-recognized BBB-protective actions of these drugs.

Salvianolic Acid Alleviated Blood-Brain Barrier Permeability in Spontaneously Hypertensive Rats by Inhibiting Apoptosis in Pericytes via P53 and the Ras/Raf/MEK/ERK Pathway

Objective

To investigate the effect of salvianolic acid A (SA) on the permeability of blood–brain barrier (BBB) and brain microvascular pericyte apoptosis in spontaneously hypertensive rats (SHR).

Methods

Evans Blue was used to determine the BBB permeability in control rats and SHR. Western blotting was used to evaluate the expression levels of relevant proteins in the pericytes isolated from the differentially treated animals. An in vitro model of hypertension was established by stimulating pericytes with angiopoietin-2 (Ang2). MTT assay was used to assess cell viability, and apoptosis and cell cycle distribution were analyzed by flow cytometry.

Results

SA attenuated BBB permeability in SHR in a dose-dependent manner. It downregulated pro-apoptotic proteins including p53, p21, Fas, FasL, cleaved-caspase 3/caspase 3 and Bax in the pericytes of SHR and upregulated CDK6, cyclin D1, CDK2, cyclin E and Bcl2. In addition, SA activated the Ras/Raf/MEK/ERK pathway in a dose-dependent manner by increasing the levels of Ras, Raf, p-MEK1, p-MEK2, p-ERK1 and p-ERK2. Finally, SA reduced Ang2-induced apoptosis of cerebral microvessels pericytes and decreased the proportion of cells in the G0/G1 phase of the cell cycle by inhibiting the p53 pathway and activating the Ras/Raf/MEK/ERK pathway.

Conclusion

SA reduced BBB permeability in spontaneously hypertensive rats, possibly by inhibiting Ang2-induced apoptosis of pericytes by activating the Ras/Raf/MEK/ERK pathway.

Structure and Junctional Complexes of Endothelial, Epithelial and Glial Brain Barriers

The homeostasis of the central nervous system (CNS) is ensured by the endothelial, epithelial, mesothelial and glial brain barriers, which strictly control the passage of molecules, solutes and immune cells. While the endothelial blood-brain barrier (BBB) and the epithelial blood-cerebrospinal fluid barrier (BCSFB) have been extensively investigated, less is known about the epithelial and mesothelial arachnoid barrier and the glia limitans. Here, we summarize current knowledge of the cellular composition of the brain barriers with a specific focus on describing the molecular constituents of their junctional complexes. We propose that the brain barriers maintain CNS immune privilege by dividing the CNS into compartments that differ with regard to their role in immune surveillance of the CNS. We close by providing a brief overview on experimental tools allowing for reliable in vivo visualization of the brain barriers and their junctional complexes and thus the respective CNS compartments.

YangXue QingNao Wan, a Compound Chinese Medicine, Attenuates Cerebrovascular Hyperpermeability and Neuron Injury in Spontaneously Hypertensive Rat: Effect and Mechanism

Objective

The purpose of the study was to explore the effect of YangXue QingNao Wan (YXQNW), a compound Chinese medicine, on cerebrovascular hyperpermeability, neuronal injury, and related mechanisms in spontaneously hypertensive rat (SHR).

Methods

Fourteen-week-old male SHR were used, with Wistar Kyoto (WKY) rats as control. YXQNW (0.5 g/kg/day), enalapril (EN, 8 mg/kg/day), and nifedipine (NF, 7.1 mg/kg/day) were administrated orally for 4 weeks. To assess the effects of the YXQNW on blood pressure, the systolic blood pressure (SBP), diastolic blood pressure (DBP), and mean blood pressure (MBP) were measured. After administering the drugs for 4 weeks, the cerebral blood flow (CBF), albumin leakage from microvessels in middle cerebral artery (MCA)-dominated area, and the number and morphology of microvessels were assessed in the hippocampus area and cortex. Neuronal damage and apoptosis were assessed by Nissl staining and TUNEL staining. To assess the mechanisms of cerebrovascular hyperpermeability, we performed immunofluorescence and Western blot to assess the expression and integrity of cerebral microvascular tight junction (TJ) and caveolin-1 (Cav-1) in cortex. Energy metabolism and Src-MLC-MLCK pathway in cortex were assessed then for elucidating the underlying mechanism of the observed effect of YXQNW.

Results

Spontaneously hypertensive rat exhibited higher blood pressure, Evans blue (EB) extravasation, albumin leakage, increased brain water content, decreased CBF, perivascular edema, and neuronal apoptosis in the hippocampus and cortex, all of which were attenuated by YXQNW treatment. YXQNW inhibited the downregulation of TJ proteins, mitochondrial Complex I, Complex II, and Complex V, and upregulation of caveolin-1, inhibiting Src/MLCK/MLC signaling in SHR. YXQNW combined with EN + NF revealed a better effect for some outcomes compared with either YXQNW or EN + NF alone.

Conclusion

The overall result shows the potential of YXQNW to attenuate blood–brain barrier (BBB) breakdown in SHR, which involves regulation of energy metabolism and Src/MLCK/MLC signaling. This result provides evidence supporting the application of YXQNW as an adjuvant management for hypertensive patients to prevent hypertensive encephalopathy.

Claudin-12 is not required for blood-brain barrier tight junction function

BACKGROUND

The blood-brain barrier (BBB) ensures central nervous system (CNS) homeostasis by strictly controlling the passage of molecules and solutes from the bloodstream into the CNS. Complex and continuous tight junctions (TJs) between brain endothelial cells block uncontrolled paracellular diffusion of molecules across the BBB, with claudin-5 being its dominant TJs protein. However, claudin-5 deficient mice still display ultrastructurally normal TJs, suggesting the contribution of other claudins or tight-junction associated proteins in establishing BBB junctional complexes. Expression of claudin-12 at the BBB has been reported, however the exact function and subcellular localization of this atypical claudin remains unknown.

METHODS

We created claudin-12-lacZ-knock-in C57BL/6J mice to explore expression of claudin-12 and its role in establishing BBB TJs function during health and neuroinflammation. We furthermore performed a broad standardized phenotypic check-up of the mouse mutant.

RESULTS

Making use of the lacZ reporter allele, we found claudin-12 to be broadly expressed in numerous organs. In the CNS, expression of claudin-12 was detected in many cell types with very low expression in brain endothelium. Claudin-12^lacZ/lacZ C57BL/6J mice lacking claudin-12 expression displayed an intact BBB and did not show any signs of BBB dysfunction or aggravated neuroinflammation in an animal model for multiple sclerosis. Determining the precise localization of claudin-12 at the BBB was prohibited by the fact that available anti-claudin-12 antibodies showed comparable detection and staining patterns in tissues from wild-type and claudin-12^lacZ/lacZ C57BL/6J mice.

CONCLUSIONS

Our present study thus shows that claudin-12 is not essential in establishing or maintaining BBB TJs integrity. Claudin-12 is rather expressed in cells that typically lack TJs suggesting that claudin-12 plays a role other than forming classical TJs. At the same time, in depth phenotypic screening of clinically relevant organ functions of claudin-12^lacZ/lacZ C57BL/6J mice suggested the involvement of claudin-12 in some neurological but, more prominently, in cardiovascular functions.

Acute high-fat feeding leads to disruptions in glucose homeostasis and worsens stroke outcome

Chronic consumption of diets high in fat leads to obesity and can negatively affect brain function. Rodents made obese by long-term maintenance on a high-fat diet have worse outcome after experimental stroke. High-fat consumption for only three days does not induce obesity but has rapid effects on the brain including memory impairment. However, the effect of brief periods of high-fat feeding or high-fat consumption in the absence of obesity on stroke is unknown. We therefore tested the effect of an acute period of high-fat feeding (three days) in C57B/6 mice on outcome after middle cerebral artery occlusion (MCAo). In contrast to a chronic high-fat diet (7.5 months), an acute high-fat diet had no effect on body weight, adipose tissue, lipid profile or inflammatory markers (in periphery and the brain). Three days of high-fat feeding impaired glucose tolerance, increased plasma glucose and insulin and brain expression of the glucose transporter GLUT-1. Ischaemic damage was increased (48%) in mice fed an acute high-fat diet, and was associated with a further reduction in GLUT-1 in the ischaemic hemisphere. These data demonstrate that only a brief period of high-fat consumption has a negative effect on glucose homeostasis and worsens outcome after ischaemic stroke.

Toxic effects of combined treatment of 1,2-dichloroethane and ethanol on mouse brain and the related mechanisms

The aim of this study was to explore the mechanisms of brain damage induced by the combined treatment of mice with 1,2-dichloroethane (1,2-DCE) and ethanol. Mice were divided into control group; 1,2-DCE-intoxicated group; ethanol-treated group; and low-, medium-, and high-dose combined treatment groups. Histological observations along with brain organ coefficients and water content were used to measure the brain damage directly and indirectly. The levels of nonprotein sulfhydryls, malondialdehyde (MDA), and superoxide dismutase activity were used as parameters to evaluate oxidative stress in the brain. Protein and messenger RNA (mRNA) levels of cytochrome P450 2E1 (CYP2E1), zonula occludens-1 (occludin and zo-1), aquaporin-4 (AQP4), nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase (HO)-1, and the γ-glutamyl cysteine synthetase catalytic and modulatory subunits (γ-GCSc, GR, and γ-GCSm) in the brain were examined by Western blot analysis and quantitative polymerase chain reaction analysis, respectively. Effects of the combined treatment of 1,2-DCE and ethanol were evaluated by analysis of variance with a factorial design. The results suggested that combined exposure to ethanol and 1,2-DCE synergistically increased CYP2E1 protein and mRNA levels, accelerated the metabolism of ethanol and 1,2-DCE in the brain tissue, induced high production of reactive oxygen species (ROS), and increased MDA levels, thereby damaging the blood-brain barrier and causing obvious pathological changes in brain tissue. However, the increased level of ROS activated the Nrf2 signal transduction pathway, promoting the expression of HO-1 and glutathione-related antioxidant enzymes in the brain to protect the cells from oxidative damage.

Vascular tight junction disruption and angiogenesis in spontaneously hypertensive rat with neuroinflammatory white matter injury

Vascular cognitive impairment is a major cause of dementia caused by chronic hypoxia, producing progressive damage to white matter (WM) secondary to blood-brain barrier (BBB) opening and vascular dysfunction. Tight junction proteins (TJPs), which maintain BBB integrity, are lost in acute ischemia. Although angiogenesis is critical for neurovascular remodeling, less is known about its role in chronic hypoxia. To study the impact of TJP degradation and angiogenesis during pathological progression of WM damage, we used the spontaneously hypertensive/stroke prone rats with unilateral carotid artery occlusion and Japanese permissive diet to model WM damage. MRI and IgG immunostaining showed regions with BBB damage, which corresponded with decreased endothelial TJPs, claudin-5, occludin, and ZO-1. Affected WM had increased expression of angiogenic factors, Ki67, NG2, VEGF-A, and MMP-3 in vascular endothelial cells and pericytes. To facilitate the study of angiogenesis, we treated rats with minocycline to block BBB disruption, reduce WM lesion size, and extend survival. Minocycline-treated rats showed increased VEGF-A protein, TJP formation, and oligodendrocyte proliferation. We propose that chronic hypoxia disrupts TJPs, increasing vascular permeability, and initiating angiogenesis in WM. Minocycline facilitated WM repair by reducing BBB damage and enhancing expression of TJPs and angiogenesis, ultimately preserving oligodendrocytes.

The ameliorative effect of bloodletting puncture at hand twelve Jing-well points on cerebral edema induced by permanent middle cerebral ischemia via protecting the tight junctions of the blood-brain barrier

Background

Cerebral edema, erupting simultaneously with severe ischemic stroke, might lead to increased intracranial pressure, cerebral herniation, and ultimately death. Studies conducted previously by our team have demonstrated the fact that bloodletting puncture at hand twelve Jing-well points (HTWP) could alleviate cerebral edema, which mainly results from the disruption of blood-brain barrier (BBB). The study, therefore, was first designed to demonstrate whether BBB-protection serves an important role in the edema-relief effect of HTWP bloodletting, based on which to research the molecular mechanism underlying.

Methods

The rats were made into model suffering from permanent middle cerebral artery occlusion (pMCAO) and then bloodletting puncture were treated at HTWP once a day. Wet and dry weight method was adopted to evaluate the degree of brain edema, evans blue extravasation and electron microscopy were used to evaluate the integrity of the BBB, and RT-qPCR was carried out to analyze the expression level of occludin, claudin-5, ICAM-1, and VEGF.

Results

Results revealed that bloodletting puncture treatment could reduce water content of brain and the permeability of BBB caused by ischemic stroke. In bloodletting puncture group, ameliorated tight junctions could be observed under electron microscopy. It was demonstrated in further study that, in bloodletting group, compared with pMCAO one, the expression levels of occludin and claudin-5 were up-regulated, while ICAM-1 and VEGF were down-regulated.

Conclusions

In conclusion, bloodletting puncture at HTWP might play a significant role in protecting the tight junctions of BBB, thus alleviating cerebral edema induced by ischemic stroke. Therefore, the therapy of bloodletting puncture at HTWP may be a promising strategy for acute ischemic stroke in the future.

Occludin as a functional marker of vascular endothelial cells on tube-forming activity

Cell therapy using endothelial progenitor cells (EPCs) is a promising strategy for the treatment of ischemic diseases. Two types of EPCs have been identified: early EPCs and late EPCs. Late EPCs are able to form tube structure by themselves, and have a high proliferative ability. The functional marker(s) of late EPCs, which relate to their therapeutic potential, have not been fully elucidated. Here we compared the gene expression profiles of several human cord blood derived late EPC lines which exhibit different tube formation activity, and we observed that the expression of occludin (OCLN) in these lines correlated with the tube formation ability, suggesting that OCLN is a candidate functional marker of late EPCs. When OCLN was knocked down by transfecting siRNA, the tube formation on Matrigel, the S phase + G₂ /M phase in the cell cycle, and the spheroid-based sprouting of late EPCs were markedly reduced, suggesting the critical role of OCLN in tube formation, sprouting, and proliferation. These results indicated that OCLN plays a novel role in neovascularization and angiogenesis.

Retinal biomarkers provide "insight" into cortical pharmacology and disease

The retina is an easily accessible out-pouching of the central nervous system (CNS) and thus lends itself to being a biomarker of the brain. More specifically, the presence of neuronal, vascular and blood-neural barrier parallels in the eye and brain coupled with fast and inexpensive methods to quantify retinal changes make ocular biomarkers an attractive option. This includes its utility as a biomarker for a number of cerebrovascular diseases as well as a drug pharmacology and safety biomarker for the CNS. It is a rapidly emerging field, with some areas well established, such as stroke risk and multiple sclerosis, whereas others are still in development (Alzheimer's, Parkinson's, psychological disease and cortical diabetic dysfunction). The current applications and future potential of retinal biomarkers, including potential ways to improve their sensitivity and specificity are discussed. This review summarises the existing literature and provides a perspective on the strength of current retinal biomarkers and their future potential.

Species variation in pesticide-induced blood-brain barrier dysfunction

Neurological disorders following acute or chronic exposure to pesticides have been reported in a number of human cases. However, the mechanism(s) by which pesticides produce central nervous system dysfunction is not clear. The objective of the present study was to examine the functional status of blood-brain barrier (BBB) in rats and mice exposed to selected pesticides of different chemical groups. Adult male albino rats and mice were exposed (1/10 of LD50) daily to dichlorvos (organophosphate), lindane (organochlorine) and carbofuran (carbamate) through oral intubation for 3 days. The status of BBB was evaluated by determining brain sodium fluorescein dye uptake and brain uptake index (BUI) in relation to serum dye level. The brain dye uptake and BUI in pesticide-exposed rats did not differ significantly in comparison to that of controls. However, brain dye uptake and BUI were increased significantly in mice exposed to dichlorvos (85%, 40%), lindane (79%, 26%) and carbofuran (129%, 61%). The results of this study show that mouse BBB system is more sensitive to pesticide-induced breach as compared to that of rat. These variations may have a role in determining the outcome of pesticide neurotoxicity in different species.

Apicobasal polarity of brain endothelial cells

Normal brain homeostasis depends on the integrity of the blood-brain barrier that controls the access of nutrients, humoral factors, and immune cells to the CNS. The blood-brain barrier is composed mainly of brain endothelial cells. Forming the interface between two compartments, they are highly polarized. Apical/luminal and basolateral/abluminal membranes differ in their lipid and (glyco-)protein composition, allowing brain endothelial cells to secrete or transport soluble factors in a polarized manner and to maintain blood flow. Here, we summarize the basic concepts of apicobasal cell polarity in brain endothelial cells. To address potential molecular mechanisms underlying apicobasal polarity in brain endothelial cells, we draw on investigations in epithelial cells and discuss how polarity may go awry in neurological diseases.

Differential gene expression in multiple neurological, inflammatory and connective tissue pathways in a spontaneous model of human small vessel stroke

AIMS

Cerebral small vessel disease (SVD) causes a fifth of all strokes plus diffuse brain damage leading to cognitive decline, physical disabilities and dementia. The aetiology and pathogenesis of SVD are unknown, but largely attributed to hypertension or microatheroma.

METHODS

We used the spontaneously hypertensive stroke-prone rat (SHRSP), the closest spontaneous experimental model of human SVD, and age-matched control rats kept under identical, non-salt-loaded conditions, to perform a blinded analysis of mRNA microarray, qRT-PCR and pathway analysis in two brain regions (frontal and mid-coronal) commonly affected by SVD in the SHRSP at age five, 16 and 21 weeks.

RESULTS

We found gene expression abnormalities, with fold changes ranging from 2.5 to 59 for the 10 most differentially expressed genes, related to endothelial tight junctions (reduced), nitric oxide bioavailability (reduced), myelination (impaired), glial and microglial activity (increased), matrix proteins (impaired), vascular reactivity (impaired) and albumin (reduced), consistent with protein expression defects in the same rats. All were present at age 5 weeks thus predating blood pressure elevation. 'Neurological' and 'inflammatory' pathways were more affected than 'vascular' functional pathways.

CONCLUSIONS

This set of defects, although individually modest, when acting in combination could explain the SHRSP's susceptibility to microvascular and brain injury, compared with control rats. Similar combined, individually modest, but multiple neurovascular unit defects, could explain susceptibility to spontaneous human SVD.

Single-Nucleotide Polymorphisms of Tight Junction Component Claudin-1 Associated with Leukoaraiosis

BACKGROUND

The blood-brain barrier (BBB) plays a major role in the development of leukoaraiosis (LA). The junctional complex of BBB consists of tight junction (TJ) and adherens junction (AJ). Claudin-1 is the integral component of TJ. The aim of this study was to evaluate whether genetic variations in claudin-1 gene are associated with the development of LA.

METHODS

LA has to be diagnosed based on images. A total of 228 LA cases and 203 controls were enrolled from the individuals who underwent brain magnetic resonance imaging with obtainable vascular risk factors. Genotyping of claudin-1 single-nucleotide polymorphisms (SNPs) (rs17501010, rs893051, and rs9290927) was performed by real-time polymerase chain reaction with LightSNiP reagents (coupled primer and probe) and FastStart DNAMaster HybProbe (Roche Diagnostic, GmBH, Mannheim, Germany) in LightCycler 2.0.

RESULTS

Among the 3 SNPs of claudin-1, a significant genetic difference was found only between control and LA (both LA-periventricular white matter [PVWM] and LA-subcortical deep white matter) with SNP rs9290927. However, their haplotypes G-G-T and G-C-A were significantly different between LA-PVWM and control, which increase the development of LA-PVWM with odds ratios of 1.45 and .57, respectively.

CONCLUSIONS

This study demonstrated first evidence of genetic polymorphism of TJ component claudin-1 and their haplotypes associated with LA.

Quercetin and isorhamnetin aglycones are the main metabolites of dietary quercetin in cerebrospinal fluid

SCOPE

Reports on the protective effect of certain foods on brain functions are numerous; however, the permeability of the brain barriers by food components is still hardly recognised. There have been in vitro studies aimed at demonstrating this possibility, but not much is known about this phenomenon in in vivo systems. The objective of the study was to determine the metabolites of dietary quercetin (Q) in urine, blood plasma and cerebrospinal fluid (CSF) after intra-rumen administration of Q rich onion dry skin in an animal model.

METHODS AND RESULTS

Eleven sheep had permanently implanted cannulas in the third ventricle of the brain as the means for CSF collection. The animals were administered Q at the dose of 10 mg/kg bwt. For 12 h the concentration of Q metabolites was measured in urine, blood plasma, and CSF. It was demonstrated that while in blood plasma Q and isorhamnetin mono-glucuronides or mono-sulphates were the main metabolites (80%), in CSF their aglycones were the dominating ones (88%).

CONCLUSION

Q and IR aglycones are the main Q metabolites present in CSF after dietary Q intake. Their passive transport through blood-CSF barrier or a de-conjugating mechanism within that barrier may be involved.

"You Shall Not Pass"-tight junctions of the blood brain barrier

The structure and function of the barrier layers restricting the free diffusion of substances between the central nervous system (brain and spinal cord) and the systemic circulation is of great medical interest as various pathological conditions often lead to their impairment. Excessive leakage of blood-borne molecules into the parenchyma and the concomitant fluctuations in the microenvironment following a transient breakdown of the blood-brain barrier (BBB) during ischemic/hypoxic conditions or because of an autoimmune disease are detrimental to the physiological functioning of nervous tissue. On the other hand, the treatment of neurological disorders is often hampered as only minimal amounts of therapeutic agents are able to penetrate a fully functional BBB or blood cerebrospinal fluid barrier. An in-depth understanding of the molecular machinery governing the establishment and maintenance of these barriers is necessary to develop rational strategies allowing a controlled delivery of appropriate drugs to the CNS. At the basis of such tissue barriers are intimate cell-cell contacts (zonulae occludentes, tight junctions) which are present in all polarized epithelia and endothelia. By creating a paracellular diffusion constraint TJs enable the vectorial transport across cell monolayers. More recent findings indicate that functional barriers are already established during development, protecting the fetal brain. As an understanding of the biogenesis of TJs might reveal the underlying mechanisms of barrier formation during ontogenic development numerous in vitro systems have been developed to study the assembly and disassembly of TJs. In addition, monitoring the stage-specific expression of TJ-associated proteins during development has brought much insight into the “developmental tightening” of tissue barriers. Over the last two decades a detailed molecular map of transmembrane and cytoplasmic TJ-proteins has been identified. These proteins not only form a cell-cell adhesion structure, but integrate various signaling pathways, thereby directly or indirectly impacting upon processes such as cell-cell adhesion, cytoskeletal rearrangement, and transcriptional control. This review will provide a brief overview on the establishment of the BBB during embryonic development in mammals and a detailed description of the ultrastructure, biogenesis, and molecular composition of epithelial and endothelial TJs will be given.

Transporters at CNS barrier sites: obstacles or opportunities for drug delivery?

The blood-brain barrier (BBB) and blood-cerebrospinal fluid (BCSF) barriers are critical determinants of CNS homeostasis. Additionally, the BBB and BCSF barriers are formidable obstacles to effective CNS drug delivery. These brain barrier sites express putative influx and efflux transporters that precisely control permeation of circulating solutes including drugs. The study of transporters has enabled a shift away from "brute force" approaches to delivering drugs by physically circumventing brain barriers towards chemical approaches that can target specific compounds of the BBB and/or BCSF barrier. However, our understanding of transporters at the BBB and BCSF barriers has primarily focused on understanding efflux transporters that efficiently prevent drugs from attaining therapeutic concentrations in the CNS. Recently, through the characterization of multiple endogenously expressed uptake transporters, this paradigm has shifted to the study of brain transporter targets that can facilitate drug delivery (i.e., influx transporters). Additionally, signaling pathways and trafficking mechanisms have been identified for several endogenous BBB/BCSF transporters, thereby offering even more opportunities to understand how transporters can be exploited for optimization of CNS drug delivery. This review presents an overview of the BBB and BCSF barrier as well as the many families of transporters functionally expressed at these barrier sites. Furthermore, we present an overview of various strategies that have been designed and utilized to deliver therapeutic agents to the brain with a particular emphasis on those approaches that directly target endogenous BBB/BCSF barrier transporters.

The beneficial effect of melatonin in brain endothelial cells against oxygen-glucose deprivation followed by reperfusion-induced injury

Melatonin has a cellular protective effect in cerebrovascular and neurodegenerative diseases. Protection of brain endothelial cells against hypoxia and oxidative stress is important for treatment of central nervous system (CNS) diseases, since brain endothelial cells constitute the blood brain barrier (BBB). In the present study, we investigated the protective effect of melatonin against oxygen-glucose deprivation, followed by reperfusion- (OGD/R-) induced injury, in bEnd.3 cells. The effect of melatonin was examined by western blot analysis, cell viability assays, measurement of intracellular reactive oxygen species (ROS), and immunocytochemistry (ICC). Our results showed that treatment with melatonin prevents cell death and degradation of tight junction protein in the setting of OGD/R-induced injury. In response to OGD/R injury of bEnd.3 cells, melatonin activates Akt, which promotes cell survival, and attenuates phosphorylation of JNK, which triggers apoptosis. Thus, melatonin protects bEnd.3 cells against OGD/R-induced injury.

Bleeding propensity of cavernous malformations: impact of tight junction alterations on the occurrence of overt hematoma

OBJECT

Endothelial tight junction (TJ) expression is mostly absent in cerebral cavernous malformations (CMs), which causes increased perilesional erythrocyte and fluid oozing. However, in a subset of CM lesions, foci of preserved TJ staining are observed along endothelial cell contacts. The clinical relevance of this finding is unclear. This study investigates the relevance of the focal TJ protein expression and its association with CM bleeding propensity.

METHODS

Immunohistochemical staining for the TJ proteins claudin-5, occludin, and ZO-1 was performed on 32 CM specimens that were resected during 2008-2010. The patients were allocated to 2 groups according to TJ protein expression, and the clinical and radiological parameters of aggressiveness were analyzed and compared. RESULTS Complete absence of TJ expression was identified in 20 specimens, and focal TJ protein expression in 12. CMs without TJ immunoreactivity were significantly larger (p = 0.022) and had a significantly greater propensity for development of frank hematomas (p = 0.028) and perilesional edema (p = 0.013). Symptom severity, multiplicity, developmental venous anomaly (DVA) presence, and CM location did not show a significant difference depending on TJ expression.

CONCLUSIONS

In a univariate analysis the authors observed significantly less propensity for frank hematomas and perilesional edema as well as smaller size in CM lesions with focal TJ expression compared with CMs without TJ expression. The observed difference in TJ protein expression might be the reason for differences in bleeding propensity of the CM lesions. Although this finding cannot be used in predictive manner at this time, it is a basis for further multivariate analyses of possible CM biological predictors.

Diversified expression of NG2/CSPG4 isoforms in glioblastoma and human foetal brain identifies pericyte subsets

NG2/CSPG4 is a complex surface-associated proteoglycan (PG) recognized to be a widely expressed membrane component of glioblastoma (WHO grade IV) cells and angiogenic pericytes. To determine the precise expression pattern of NG2/CSPG4 on glioblastoma cells and pericytes, we generated a panel of >60 mouse monoclonal antibodies (mAbs) directed against the ectodomain of human NG2/CSPG4, partially characterized the mAbs, and performed a high-resolution distributional mapping of the PG in human foetal, adult and glioblastoma-affected brains. The reactivity pattern initially observed on reference tumour cell lines indicated that the mAbs recognized 48 immunologically distinct NG2/CSPG4 isoforms, and a total of 14 mAbs was found to identify NG2/CSPG4 isoforms in foetal and neoplastic cerebral sections. These were consistently absent in the adult brain, but exhibited a complementary expression pattern in angiogenic vessels of both tumour and foetal tissues. Considering the extreme pleomorphism of tumour areas, and with the aim of subsequently analysing the distributional pattern of the NG2/CSPG4 isoforms on similar histological vessel typologies, a preliminary study was carried out with endothelial cell and pericyte markers, and with selected vascular basement membrane (VBM) components. On both tumour areas characterized by 'glomeruloid' and 'garland vessels', which showed a remarkably similar cellular and molecular organization, and on developing brain vessels, spatially separated, phenotypically diversified pericyte subsets with a polarized expression of key surface components, including NG2/CSPG4, were disclosed. Interestingly, the majority of the immunolocalized NG2/CSPG4 isoforms present in glioblastoma tissue were present in foetal brain, except for one isoform that seemed to be exclusive of tumour cells, being absent in foetal brain. The results highlight an unprecedented, complex pattern of NG2/CSPG4 isoform expression in foetal and neoplastic CNS, discriminating between phenotype-specific and neoplastic versus non-neoplastic variants of the PG, thus opening up vistas for more selective immunotherapeutic targeting of brain tumours.

The blood-brain barrier: an engineering perspective

It has been more than 100 years since Paul Ehrlich reported that various water-soluble dyes injected into the circulation did not enter the brain. Since Ehrlich's first experiments, only a small number of molecules, such as alcohol and caffeine have been found to cross the blood-brain barrier, and this selective permeability remains the major roadblock to treatment of many central nervous system diseases. At the same time, many central nervous system diseases are associated with disruption of the blood-brain barrier that can lead to changes in permeability, modulation of immune cell transport, and trafficking of pathogens into the brain. Therefore, advances in our understanding of the structure and function of the blood-brain barrier are key to developing effective treatments for a wide range of central nervous system diseases. Over the past 10 years it has become recognized that the blood-brain barrier is a complex, dynamic system that involves biomechanical and biochemical signaling between the vascular system and the brain. Here we reconstruct the structure, function, and transport properties of the blood-brain barrier from an engineering perspective. New insight into the physics of the blood-brain barrier could ultimately lead to clinical advances in the treatment of central nervous system diseases.

Is the ischemic blood–brain barrier insufficiency responsible for full-blown Alzheimer's disease?

The goal of this paper is to provide scientists with a comprehensive review of the state-of-the-art influence the ischemic blood-brain barrier (BBB) has on the final development of Alzheimer's disease and to provide detailed food-for-thought which will hopefully stimulate more researchers in this area of neuroscience. Understanding new and fundamental concepts about the behavior of the BBB during long-term reperfusion after ischemia with a variety of new neuropathogenic factors can hopefully provide some interesting clues related to the pathologic processes issues that have been receiving considerable attention in the human clinic. We present the recent data to understand the role of the BBB in maturation of both diseases and try to differentiate between primary and secondary pathologic mechanisms. In conclusion, the neuropathogenesis of Alzheimer's disease involves an initial ischemic neuronal alterations leading to enhanced neuronal vulnerability to beta-amyloid peptide and the ischemic breakdown of the BBB with leakage of serum borne beta-amyloid peptide into brain parenchyma, activation of beta-amyloid peptide-dependent toxicity culminating in the formation of amyloid plaques and finally end in full-blown Alzheimer's disease. In summary, probably we have combined mechanism(s) of ischemia processes, ischemic and chronic BBB dysfunction and beta-amyloid peptide-dependent injury in pathology of neurodegeneration that is observed in Alzheimer's disease. We speculate that Alzheimer's disease may be caused by silent and sublethal ischemic episodes that attack and slowly steal the minds of its victims. Finally, our review proposes the ischemic BBB-dependent mechanism(s) that probably are responsible for full-blown Alzheimer's disease.

Kruppel-like factor 2 protects against ischemic stroke by regulating endothelial blood brain barrier function

During an ischemic stroke normal brain endothelial function is perturbed, resulting in blood brain barrier (BBB) breakdown with subsequent infiltration of activated inflammatory blood cells, ultimately leading to neuronal cell death. Kruppel-like factor 2 (KLF2) is regulated by flow, is highly expressed in vascular endothelial cells (ECs), and serves as a key molecular switch regulating endothelial function and promoting vascular health. In this study we sought to determine the role of KLF2 in cerebrovascular function and the pathogenesis of ischemic stroke. Transient middle cerebral artery occlusion was performed in KLF2-deficient (KLF2(-/-)), KLF2 overexpressing (KLF2(tg)), and control mice, and stroke volume was analyzed. BBB function was assessed in vivo by real-time neuroimaging using positron emission tomography and Evan's blue dye assay. KLF2(-/-) mice exhibited significantly larger strokes and impairment in BBB function. In contrast, KLF2(tg) mice were protected against ischemic stroke and demonstrated preserved BBB function. In concordance, gain- and loss-of-function studies in primary brain microvascular ECs using transwell assays revealed KLF2 to be BBB protective. Mechanistically, KLF2 was demonstrated, both in vitro and in vivo, to regulate the critical BBB tight junction factor occludin. These data are first to identify endothelial KLF2 as a key regulator of the BBB and a novel neuroprotective factor in ischemic stroke.

Telmisartan protects against cognitive decline via up-regulation of brain-derived neurotrophic factor/tropomyosin-related kinase B in hippocampus of hypertensive rats

BACKGROUND AND PURPOSE

Cognitive decline may occur as a result of hypertension, and is dependent on the function of hippocampus. Brain-derived neurotrophic factor (BDNF) mediated by angiotensin II-induced oxidative stress protects against cell death in hippocampus. Angiotensin II receptor blocker (ARB), candesartan, activates BDNF in the hippocampus. Furthermore, peroxisome proliferator-activated receptor (PPAR)-gamma activation in the brain prevents brain damage. Telmisartan, a unique ARB with PPAR-gamma stimulating activity, protects against cognitive decline partly because of PPAR-gamma activation. The aim of the present study was to determine whether telmisartan protects against cognitive decline via up-regulation of BDNF and its receptor tropomyosin-related kinase B (TrkB) in the hippocampus of hypertensive rats, partly because of PPAR-gamma activation.

METHODS AND RESULTS

We divided stroke-prone spontaneously hypertensive rats (SHRSPs), as hypertensive and vascular dementia model rats, into five groups, telmisartan-treated (TLM), TLM+GW9662, a PPAR-gamma inhibitor, -treated (T+G), GW9662-treated (GW), TLM+ANA-12, a TrkB antagonist, -treated (T+A), and vehicle-treated SHRSPs (VEH). After the treatment for 28 days, systolic blood pressure did not change in all groups. However, BDNF expression in the hippocampus was significantly higher in TLM than in VEH to a greater extent than in T+G. Cognitive performance was significantly higher in TLM than in VEH to a greater extent than in T+G, and was not different between T+A, GW, and VEH.

CONCLUSION

Telmisartan protects against cognitive decline via up-regulation of BDNF/TrkB in the hippocampus of SHRSPs, partly because of PPAR-gamma activation independent of blood pressure-lowering effect.

Deficiency of NG2+ cells contributes to the susceptibility of stroke-prone spontaneously hypertensive rats

AIMS

The purpose of this study is to investigate whether the NG2(+) cells, a class of oligodendrocyte progenitor cells, is involved in the pathophysiology of stroke in stroke-prone spontaneously hypertensive rat (SHR-SP).

METHODS

SHR-SP, SHR, Wistar-Kyoto rats (WKY), and C57BJ/6 mice were used. Immunohistochemistry was conducted to evaluate the number of NG2(+) cells in frozen brain sections. Demyelination was evaluated by Sudan black staining and serum level of myelin basic protein. Middle cerebral artery occlusion (MCAO) was performed to prepare experimental stroke model.

RESULTS

The number of NG2(+) cells was significantly decreased in infarct core and increased in penumbra in WKY rats after MCAO. In brain sections of 6-month-old SHR-SP, the number of NG2(+) cells was significantly (P < 0.01) less than that in age-matched SHR and WKY rats. However, this phenomenon was not observed in 3-month-old rats. Demyelination was found in 6-month-old SHR-SP but not in 3-month-old SHR-SP. Pharmacological treatment of cuprizone in mice induced demyelination and enlargement of cerebral infarction after MCAO.

CONCLUSION

The decline of NG2(+) cells may cause demyelination and contribute to the susceptibility of SHR-SP to ischemic brain injury.

Epidemiology, pathophysiology, and treatment of hypertension in ischaemic stroke patients

Stroke continues to be one of the leading causes of mortality and morbidity worldwide. There are 2 main types of stroke: ischaemic strokes, which are caused by obstruction of the blood vessels leading to or within the brain, and haemorrhagic strokes, which are induced by the disruption of blood vessels. Stroke is a disease of multifactorial aetiology that may develop as an end state in patients with serious vascular conditions--most notably, uncontrolled arterial hypertension--thereby necessitating the effective control of this risk factor to prevent stroke or its recurrence. This paper focuses specifically on the epidemiology and pathogenesis of ischaemic stroke mainly in chronically hypertensive patients and pays particular attention to the efficacy of a select group of routinely used major antihypertensive drugs (i.e., angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, and calcium channel blockers) in the treatment of strokes.

Is the spontaneously hypertensive stroke prone rat a pertinent model of sub cortical ischemic stroke? A systematic review

The spontaneously hypertensive stroke prone rat is best known as an inducible model of large artery stroke. Spontaneous strokes and stroke propensity in the spontaneously hypertensive stroke prone rat are less well characterized; however, could be relevant to human lacunar stroke. We systematically reviewed the literature to assess the brain tissue and small vessel pathology underlying the spontaneous strokes of the spontaneously hypertensive stroke prone rat. We searched systematically three online databases from 1970 to May 2010; excluded duplicates, reviews, and articles describing the consequences of induced middle cerebral artery occlusion or noncerebral pathology; and recorded data describing brain region and the vessels examined, number of animals, age, dietary salt intake, vascular and tissue abnormalities. Among 102 relevant studies, animals sacrificed after developing stroke-like symptoms displayed arteriolar wall thickening, subcortical lesions, enlarged perivascular spaces and cortical infarcts and hemorrhages. Histopathology, proteomics and imaging studies suggested that the changes not due simply to hypertension. There may be susceptibility to endothelial permeability increase that precedes arteriolar wall thickening, degeneration and perivascular tissue changes; systemic inflammation may also precede cerebrovascular changes. There were very few data on venules or tissue changes before hypertension. The spontaneously hypertensive stroke prone rat shows similar features to human lacunar stroke and may be a good spontaneous model of this complex human disorder. Further studies should focus on structural changes at early ages and genetics to identify factors that predispose to vascular and brain damage.

Impairment of tight junctions and glucose transport in endothelial cells of human cerebral cavernous malformations

Cerebral cavernous malformations (CCMs) often cause hemorrhages that can result in severe clinical manifestations, including hemiparesis and seizures. The underlying mechanisms of the aggressive behavior of CCMs are undetermined to date, but alterations of vascular matrix components may be involved. We compared the localization of the tight junction proteins (TJPs) in 12 CCM specimens and the expression of glucose transporter 1 (GLUT-1), which is sensitive to alterations in TJP levels, in 5 CCM specimens with those in 5 control temporal lobectomy specimens without CCM by immunofluorescence microscopy. The TJPs occludin, claudin-5, and zonula occludens ZO-1 were downregulated at intercellular contact sites and partly redistributed within the surrounding tissue in the CCM samples; there was also a marked reduction of GLUT-1 immunoreactivity compared with that in control specimens. Corresponding analysis using quantitative real-time reverse transcription polymerase chain reaction on 8 CCM and 8 control specimens revealed significant downregulation of mRNA expression of occludin, claudin-5, ZO-1, and GLUT-1. The altered expression and localization of the TJPs at interendothelial contact sites accompanied by a reduction of GLUT-1 expression in dilated CCM microvessels likely affect vascular matrix stability and may contribute to hemorrhages of CCMs.

Tight junctions contain oligomeric protein assembly critical for maintaining blood-brain barrier integrity in vivo

Tight junctions (TJs) are major components of the blood-brain barrier (BBB) that physically obstruct the interendothelial space and restrict paracellular diffusion of blood-borne substances from the peripheral circulation to the CNS. TJs are dynamic structures whose intricate arrangement of oligomeric transmembrane and accessory proteins rapidly alters in response to external stressors to produce changes in BBB permeability. In this study, we investigate the constitutive trafficking of the TJ transmembrane proteins occludin and claudin-5 that are essential for forming the TJ seal between microvascular endothelial cells that inhibits paracellular diffusion. Using a novel, detergent-free OptiPrep density-gradient method to fractionate rat cerebral microvessels, we identify a plasma membrane lipid raft domain that contains oligomeric occludin and claudin-5. Our data suggest that oligomerization of occludin involves disulfide bond formation within transmembrane regions, and that assembly of the TJ oligomeric protein complex is facilitated by an oligomeric caveolin scaffold. This is the first time that distribution of oligomeric TJ transmembrane proteins within plasma membrane lipid rafts at the BBB has been examined in vivo. The findings reported in this study are critical to understand the mechanism of assembly of the TJ multiprotein complex that is essential for maintaining BBB integrity.

Blockade of AT1 receptors protects the blood-brain barrier and improves cognition in Dahl salt-sensitive hypertensive rats

BACKGROUND

The present study tested the hypothesis that inappropriate activation of the brain renin-angiotensin system (RAS) contributes to the pathogenesis of blood-brain barrier (BBB) disruption and cognitive impairment during development of salt-dependent hypertension. Effects of an angiotensin II (AngII) type-1 receptor blocker (ARB), at a dose that did not reduce blood pressure, were also examined.

METHODS

Dahl salt-sensitive (DSS) rats at 6 weeks of age were assigned to three groups: low-salt diet (DSS/L; 0.3% NaCl), high-salt diet (DSS/H; 8% NaCl), and high-salt diet treated with ARB, olmesartan at 1 mg/kg.

RESULTS

DSS/H rats exhibited hypertension, leakage from brain microvessels in the hippocampus, and impaired cognitive functions, which were associated with increased brain AngII levels, as well as decreased mRNA levels of tight junctions (TJs) and collagen-IV in the hippocampus. In DSS/H rats, olmesartan treatment, at a dose that did not alter blood pressure, restored the cognitive decline, and ameliorated leakage from brain microvessels. Olmesartan also decreased brain AngII levels and restored mRNA expression of TJs and collagen-IV in DSS/H rats.

CONCLUSIONS

These results suggest that during development of salt-dependent hypertension, activation of the brain RAS contributes to BBB disruption and cognitive impairment. Treatment with an ARB could elicit neuroprotective effects in cognitive disorders by preventing BBB permeability, which is independent of blood pressure changes.

Looking at the blood-brain barrier: molecular anatomy and possible investigation approaches

The blood-brain barrier (BBB) is a dynamic and complex interface between blood and the central nervous system that strictly controls the exchanges between the blood and brain compartments, therefore playing a key role in brain homeostasis and providing protection against many toxic compounds and pathogens. In this review, the unique properties of brain microvascular endothelial cells and intercellular junctions are examined. The specific interactions between endothelial cells and basement membrane as well as neighboring perivascular pericytes, glial cells and neurons, which altogether constitute the neurovascular unit and play an essential role in both health and function of the central nervous system, are also explored. Some relevant pathways across the endothelium, as well as mechanisms involved in the regulation of BBB permeability, and the emerging role of the BBB as a signaling interface are addressed as well. Furthermore, we summarize some of the experimental approaches that can be used to monitor BBB properties and function in a variety of conditions and have allowed recent advances in BBB knowledge. Elucidation of the molecular anatomy and dynamics of the BBB is an essential step for the development of new strategies directed to maintain or restore BBB integrity and barrier function and ultimately preserve the delicate interstitial brain environment.

Effect of cytisine on some brain and hepatic biochemical parameters in spontaneously hypertensive rats

Tobacco smoking is a risk factor for variety of cardio-vascular diseases, such as hypertension, myocardial infarction, stroke and many others. It is of great importance for hypertensive patients to stop smoking. One of the medicines widely used for smoking cessation in Bulgaria is the original Bulgarian product Tabex®, which is developed on the basis of natural plant alkaloid cytisine. The aim of the following study was to ivestigate the effects of cytisine on some brain and hepatic biochemical parameters in spontaneously hypertensive rats (SHR), an widely used rodent model for human essential hypertension, and to compare the obtained results with their age-matched normotensive controls Wistar Kyoto (WKY). Multiple cytisine administration did not affect the activity of ethylmorphine-N-demethylase (EMND) and anylinehydroxylase (AH), as well as the quantity of cytochrome P 450, nor in WKY neither in SHR In the liver cytisine increased the MDA quantity both in SHR and in WKY, by 25% (p<0.05) and by 29% (p<0.05) respectively, while the GSH level was not significantly changed by the compound in both strains. In contrast, on the brain level, cytisine administration to SHR caused more prominent toxicity, resulted in GSH depletion and increased MDA quantity, while in WKY strain did not exert any toxicity. Cytisine did not significantly affect ALAT and ASAT activity in both strains. In conclusion, the results of our study suggest higher brain toxicity of cytisine in spontaneously hypertensive rats, that might be due to their pathophysiological characteristics.

Angiotensin II modulates BBB permeability via activation of the AT(1) receptor in brain endothelial cells

Hypertensive encephalopathy occurs when acute changes in blood pressure cause breakdown of the blood-brain barrier (BBB). Angiotensin II (Ang II) plays a role in this pathophysiology. We determined whether Ang II directly regulates endothelial cell function at the BBB. In BBB microvessel endothelial cells (MECs), the Ang II (100 nmol/L; 0 to 6 h) effects on permeability to (125)I-albumin and transendothelial electrical resistance (TEER) were assessed. Angiotensin II (100 nmol/L) caused significant time-dependent changes in both (125)I-albumin permeability (25%) at 2 h and TEER (-8.87 Omega x cm(2)) at 6 h. Next, MECs were pretreated with the Ang II type 1 (AT(1)) receptor blocker telmisartan (1 micromol/L) or the Ang II type 2 (AT(2)) receptor blocker PD123,319 (1 micromol/L) followed by treatment with Ang II (100 nm). Telmisartan completely inhibited the Ang II-induced increase in (125)I-albumin permeability in MECs whereas PD123,319 had no effect. Using western blot analysis, we showed that MECs express AT(1) receptors but not AT(2) receptors. Treatment with Ang II (100 nmol/L; 0 to 6 h) also increased total protein kinase C activity. In contrast, Ang II had no effect on the expression of occludin, claudin 5, or actin. These results show that Ang II directly modulates transcytotic and paracellular permeability in BBB endothelial cells and could contribute to the pathophysiology of hypertensive encephalopathy.