The blood-brain barrier and cerebrovascular pathology in Alzheimer's disease

Tight junction protein expression and barrier properties of immortalized mouse brain microvessel endothelial cells

Understanding the molecular and biochemical mechanisms regulating the blood-brain barrier is aided by in vitro model systems. Many studies have used primary cultures of brain microvessel endothelial cells for this purpose. However, primary cultures limit the generation of material for molecular and biochemical assays since cells grow slowly, are prone to contamination by other neurovascular unit cells, and lose blood-brain barrier characteristics when passaged. To address these issues, immortalized cell lines have been generated. In these studies, we assessed the suitability of the immortalized mouse brain endothelial cell line, bEnd3, as a blood-brain barrier model. RT-PCR and immunofluorescence indicated expression of multiple tight junction proteins. bEnd3 cells formed barriers to radiolabeled sucrose, and responded like primary cultures to disrupting stimuli. Exposing cells to serum-free media on their basolateral side significantly decreased paracellular permeability; astrocyte-conditioned media did not enhance barrier properties. The serum-free media-induced decrease in permeability was correlated with an increase in claudin-5 and zonula occludens-1 immunofluorescence at cell-cell contracts. We conclude that bEnd3 cells are an attractive candidate as a model of the blood-brain barrier due to their rapid growth, maintenance of blood-brain barrier characteristics over repeated passages, formation of functional barriers and amenability to numerous molecular interventions.

The possible role of capillary cerebral amyloid angiopathy in Alzheimer lesion development: a regional comparison

Recent studies have observed beta-amyloid-positive capillaries in lesion-prone regions of Alzheimer's disease (AD) brains. It is possible that there is a pathogenic link between neurofibrillary tangles (NFTs) and/or senile plaques (SPs) and altered capillary structure/function. In this study, we examined and compared brain tissue from a frequently observed NFT abundant area, the superior temporal cortex (ST), and a comparatively much NFT sparser area, the calcarine cortex (COC), in ten AD and ten normal adult control brain samples. We recorded the densities of NFTs, and beta-amyloid(8-17,40,42) peptide forms in SPs, capillaries and large vessels [cerebral amyloid angiopathy (CAA)] in these areas. Our results demonstrated that there was a significant difference between the means of NFT and SP beta(8-17,40) lesions when comparing the ST and COC cortical regions in both AD and control brains. In AD brains, we observed a positive correlation between NFTs and SPs in both regions, and between NFTs and beta-amyloid-positive capillaries and CAA vessels, particularly in the calcarine cortex. In addition, significant correlations were observed between some SP beta-amyloid peptide forms and CAA beta(42), in particular, in both regions. These new observations support the view that there are regional (focal) differences in the presence of each AD lesion, and that there may be a pathogenic relationship between the development of AD lesions and beta-amyloid-positive vessels. The data are also consistent with the concept that a focally dysfunctional blood-brain barrier (BBB) that is unable to regulate the influx/efflux of neurotoxic amyloid peptides may participate in the pathogenesis of AD lesions.

Alzheimer's disease, brain immune privilege and memory: a hypothesis

The most distinctive feature of Alzheimer's disease (AD) is the specific degeneration of the neurons involved in memory consolidation, storage, and retrieval. Patients suffering from AD forget basic information about their past, loose linguistic and calculative abilities and communication skills. Thus, understanding the etiology of AD may provide insights into the mechanisms of memory and vice versa. The brain is an immunologically privileged site protected from the organism's immune reactions by the blood-brain barrier (BBB). All risk factors for AD (both cardiovascular and genetic) lead to destruction of the BBB. Evidence emerging from recent literature indicates that AD may have an autoimmune nature associated with BBB impairments. This hypothesis suggests that the process of memory consolidation involves the synthesis of novel macromolecules recognized by the immune system as "non-self" antigens. The objective of this paper is to stimulate new approaches to studies of neural mechanisms underpinning memory consolidation and its breakdown during AD. If the hypothesis on the autoimmune nature of AD is correct, the identification of the putative antigenic macromolecules might be critical to understanding the etiology and prevention of AD, as well as for elucidating cellular mechanisms of learning and memory.

Comparative proteomics of cerebrospinal fluid in neuropathologically-confirmed Alzheimer's disease and non-demented elderly subjects

OBJECTIVES

Diagnostic tests able to reveal Alzheimer's disease (AD) in living patients before cognitive ability is destroyed are urgently needed. Such tests must distinguish AD from other dementia causes, as well as differentiate subtle changes associated with normal aging from true pathology emergence. A single biomarker offering such diagnostic and prognostic capacities has eluded identification. Therefore, a valuable test for AD is likely to be based on a specific pattern of change in a set of proteins, rather than a single protein.

METHODS

We examined pooled cerebrospinal fluid (CSF) samples obtained from neuropathologically-confirmed AD (n=43) and non-demented control subjects (n=43) using 2-dimensional gel electrophoresis (2DE) proteomic methodology to detect differentially expressed proteins. Proteins exhibiting expression level differences between the pools were recovered and identified using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry.

RESULTS

Five differentially-expressed proteins with potential roles in amyloid-beta metabolism and vascular and brain physiology [apolipoprotein A-1 (Apo A-1), cathepsin D (CatD), hemopexin (HPX), transthyretin (TTR), and two pigment epithelium-derived factor (PEDF) isoforms] were identified. Apo A-1, CatD and TTR were significantly reduced in the AD pool sample, while HPX and the PEDF isoforms were increased in AD CSF.

DISCUSSION

These results suggest that multi-factor proteomic pattern analysis of the CSF may provide a means to diagnose and assess AD.

Astrocyte-endothelial interactions at the blood-brain barrier

The blood-brain barrier, which is formed by the endothelial cells that line cerebral microvessels, has an important role in maintaining a precisely regulated microenvironment for reliable neuronal signalling. At present, there is great interest in the association of brain microvessels, astrocytes and neurons to form functional 'neurovascular units', and recent studies have highlighted the importance of brain endothelial cells in this modular organization. Here, we explore specific interactions between the brain endothelium, astrocytes and neurons that may regulate blood-brain barrier function. An understanding of how these interactions are disturbed in pathological conditions could lead to the development of new protective and restorative therapies.

Type 2 diabetes is negatively associated with Alzheimer's disease neuropathology

BACKGROUND

In cross-sectional and longitudinal studies, type 2 diabetes has been positively associated with the risk of Alzheimer's disease (AD). The present descriptive study compared diabetic and nondiabetic subjects on the severity of neuritic plaques and neurofibrillary tangles (NFTs) in the cerebral cortex and in the hippocampus.

METHODS

The study included specimens from 385 consecutive autopsies of residents of a nursing home (15.8% diabetics). Mean age at death = 84 years [standard deviation (SD) = 10], 66% were female, Clinical Dementia Rating mean = 3.0 (SD = 1.6), and 32.5% had an APOE4 allele. Additional analyses limited the sample to 268 subjects (14.1% diabetics) without neuropathology other than AD.

RESULTS

Analyses of covariance controlling for age at death, dementia severity (Clinical Dementia Rating score), and APOE4 allele indicated that diabetics had significantly fewer neuritic plaques (p =.008) and NFTs (p =.047) in the cerebral cortex than did nondiabetics. In the hippocampus, diabetics had significantly lower plaque ratings than did nondiabetics (p =.019), but the lower ratings of NFTs did not achieve statistical significance (p =.082). In the entire sample, diabetics had significantly less AD-associated neuropathology in all four analyses.

CONCLUSIONS

These results raise the possibility that the varied associations observed between diabetes and AD may be specific to as yet ill-defined subgroups of dementia and diabetic patients or may be more characteristic of younger patients than of those who survive to a mean age of 84 years. Future studies are encouraged to examine a variety of other characteristics such as age that may interact with diabetes affecting the incidence of AD.

Ethanol-Induced Activation of Myosin Light Chain Kinase Leads to Dysfunction of Tight Junctions and Blood-Brain Barrier Compromise

BACKGROUND

Brain endothelial cells form the blood-brain barrier (BBB) that regulates solute and macromolecule flux in and out of the brain, leukocyte migration, and maintains the homeostasis of the central nervous system. BBB dysfunction is associated with disruption of tight junctions (TJ) in the brain endothelium. We propose that alcohol abuse may impair BBB permeability through TJ modification.

METHODS

Primary cultured bovine brain microvascular endothelial cells (BBMEC) were treated with 50 mM ethanol (EtOH), and monolayer tightness was assessed by measurement of transendothelial electrical resistance (TEER). Changes in TEER were correlated with alterations in TJ protein distribution [occludin, zonula occludens-1 (ZO-1), claudin-5] using immunofluorescence (IF). Expression of myosin light chain (MLC) kinase (MLCK), ZO-1, claudin-5, and phosphorylated MLC, occludin and claudin-5 were determined by immunoprecipitation and Western blot. EtOH-induced changes in monocyte migration across in vitro BBB constructs were also examined.

RESULTS

EtOH induced a decrease in TEER of BBMEC monolayers that was reversed by EtOH withdrawal. Treatment of BBMEC with EtOH or its metabolite, acetaldehyde, prior to monocyte application resulted in a 2-fold increase in monocyte migration across the BBB. IF demonstrated decrease in claudin-5 staining, occludin translocation from cell borders to cytoplasm and gap formation in EtOH-treated BBMEC monolayer. These changes paralleled significant increase in phosphorylation of MLC, occludin and claudin-5. EtOH-treated BBMEC showed reduction of total occludin and claudin-5 without changes in ZO-1 or MLC. TEER decrease, changes in occludin/claudin staining, increase in MLC, occludin and claudin-5 phosphorylation and enhanced monocyte migration across the BBB were all reversed by inhibition of MLCK. Inhibition of EtOH metabolism in BBMEC also reversed these events.

CONCLUSION

These results suggest that EtOH activates MLCK leading to phosphorylation of MLC, occludin and claudin-5. Cytoskeletal alterations (MLC) and TJ changes (occludin and claudin-5 phosphorylation) result in BBB impairment (decrease in TEER). TJ compromise is associated with increased monocyte migration across the BBB.

Hypoxia-inducible factor and nuclear factor kappa-B activation in blood-brain barrier endothelium under hypoxic/reoxygenation stress

This investigation focuses on transcription factor involvement in blood-brain barrier (BBB) endothelial cell-induced alterations under conditions of hypoxia and post-hypoxia/reoxygenation (H/R), using established in vivo/ex vivo and in vitro BBB models. Protein/DNA array analyses revealed a correlation in key transcription factor activation during hypoxia and H/R, including NFkappaB and hypoxia-inducible factor (HIF)1. Electrophoretic mobility shift assays confirmed NFkappaB and HIF1 binding activity ex vivo and in vitro, under conditions of hypoxia and H/R. Hypoxia- and H/R-treated BBB endothelium showed increased HIF1alpha protein expression in both cytoplasmic and nuclear fractions, in ex vivo and in vitro models. Co-immunoprecipitation of HIF1alpha and HIF1beta was shown in the nuclear fraction under conditions of hypoxia and H/R in both models. Hypoxia- and H/R-treated BBB endothelium showed increased expression of NFkappaB-p65 protein in both cytoplasmic and nuclear fractions. Co-immunoprecipitation of NFkappaB-p65 with NFkappaB-p50 was shown in the nuclear fraction under conditions of hypoxia and H/R in the ex vivo model, and after H/R in the in vitro model. These data offer novel avenues in which to alter and/or investigate BBB activity across model systems and to further our understanding of upstream regulators during hypoxia and H/R.

Transferrin neutralization of amyloid β 25–35 cytotoxicity

BACKGROUND

Fibrillar aggregates of amyloid beta 25-35 (Abeta(25-35)) form rapidly in vitro able to lyse human red blood cells (RBCs). Human sera, albumin, and apolipoprotein E (ApoE) each limit fibrillation and cytotoxicity. Potentially, these substances protect neurons from Abeta(1-40/42) aggregates. Transferrin (TF) is investigated in this study.

METHODS

The Mattson red blood cells model was employed to determine whether co-incubation of transferrin and Abeta(25-35) prevented lysis. The formation of fibrillar Abeta(25-35) in the presence of transferrin was investigated using Congo red staining and spectrophotometric studies.

RESULTS

We found that incubation of 20 muM Abeta(25-35) with physiologic levels of transferrin prevented red blood cells lysis and the formation of macro-aggregates.

CONCLUSIONS

These in vitro results suggest that transferrin may limit fibrillar beta amyloid formation in vivo and cytotoxicity.

Cholesterol in neurologic disorders of the elderly: stroke and Alzheimer’s disease

Mechanisms for the regulation of intracellular cholesterol levels in various types of brain and vascular cells are of considerable importance in our understanding of the pathogenesis of a variety of diseases, particularly atherosclerosis and Alzheimer's disease (AD). It is increasingly clear that conversion of brain cholesterol into 24-hydroxycholesterol and its subsequent release into the periphery is important for the maintenance of brain cholesterol homeostasis. Recent studies have shown elevated plasma concentrations of 24-hydroxycholesterol in patients with AD and vascular dementia, suggesting increased brain cholesterol turnover during neurodegeneration. The oxygenases involved in the degradation and excretion of cholesterol, including the cholesterol 24-hydroxylase and the 27-hydroxylase, are enzymes of the cytochrome P-450 family. This review focuses on the newly recognized importance of cholesterol and its oxygenated metabolites in the pathogenesis of ischemic stroke and AD. The reduction in stroke and AD risk in patients treated with cholesterol-lowering statins is also discussed.

Mannitol opening of the blood-brain barrier: regional variation in the permeability of sucrose, but not 86Rb+ or albumin

Clinically, infusion of hyperosmolar solutions is used to enhance chemotherapeutic drug penetration of the blood-brain barrier (BBB) in patients with malignant brain tumors or metastases. We examined the effect of hyperosmolar BBB disruption on brain permeability of three compounds, 86Rb+, a marker for K+ permeability and transport, [14C]sucrose and Evans blue albumin, using a rat in situ perfusion model. 86Rb+ and [14C]sucrose had increased permeability 20 min after BBB disruption with 1.6 M mannitol. There was no change in Evans blue albumin permeability. Only [14C]sucrose showed regional variation in permeability after mannitol-induced BBB disruption, with the cortex and midbrain having higher sucrose permeability then either the cerebellum or brainstem. These data suggest that the clinical efficacy of hyperosmolar disruption therapy in conjunction with chemotherapeutic agents, of a similar molecular weight to sucrose, may be affected by the location of the tumor within the brain.

Protection against hypoxia-induced blood-brain barrier disruption: changes in intracellular calcium

Tissue damage after stroke is partly due to disruption of the blood-brain barrier (BBB). Little is known about the role of calcium in modulating BBB disruption. We investigated the effect of hypoxic and aglycemic stress on BBB function and intracellular calcium levels. Bovine brain microvessel endothelial cells were treated with A-23187 to increase intracellular calcium without hypoxia or treated with a calcium chelator (BAPTA) or calcium channel blockers (nifedipine or SKF-96365) and 6 h of hypoxia. A-23187 alone did not increase paracellular permeability. Hypoxia increased intracellular calcium, and hypoxia or hypoxia-aglycemia increased paracellular permeability. Treatment with nifedipine and SKF-96365 increased intracellular calcium under normoglycemic conditions, instead of blocking calcium influx, and was protective against hypoxia-induced BBB disruption under normoglycemia. Protection by nifedipine and SKF-96365 was not due to antioxidant properties of these compounds. These data indicate that increased intracellular calcium alone is not enough to disrupt the BBB. However, increased intracellular calcium after drug treatment and hypoxia suggests a potential mechanism for these drugs in BBB protection; nifedipine and SKF-96365 plus hypoxic stress may trigger calcium-mediated signaling cascades, altering BBB integrity.

Pathogenesis of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) is the result of the deposition of an amyloidogenic protein in cortical and leptomeningeal vessels. The most common type of CAA is caused by amyloid beta-protein (Abeta), which is particularly associated with Alzheimer's disease (AD). Excessive Abeta-CAA formation can be caused by several mutations in the Abeta precursor protein and presenilin genes. The origin of Abeta in CAA is likely to be neuronal, although cerebrovascular cells or the circulation cannot be excluded as a source. Despite the apparent similarity, the pathogenesis of CAA appears to differ from that of senile plaques in several aspects, including the mechanism of Abeta-induced cellular toxicity, the extent of inflammatory reaction and the role of oxidative stress. Therefore, therapeutic strategies for AD should, at least in part, also target CAA. Moreover, CAA and cerebrovascular disease (CVD) may set a lower threshold for AD-like changes to cause dementia and may even cause dementia on its own, since patients with AD and CAA and/or CVD appear to be more cognitively impaired than patients with only AD. In conclusion, the precise impact of CAA on AD or dementia remains unclear, however, its role may have been underestimated in the past, and more extensive studies of in vitro and in vivo models for CAA will be needed to elucidate the importance of CAA-specific approaches in designing intervention strategies for AD.

Brain cholinesterases: I. The clinico-histopathological and biochemical basis of Alzheimer's disease

Substantial evidence is presented demonstrating that it is the cholinesterases (ChEs) that constitute the organizer, the connector and the safeguard for multiple neurochemical functions and mature anatomical architecture of the brain. In Alzheimer's disease (AD), the histopathological characteristics are initially and primarily associated with the degeneration of the acetylcholinesterase (AChE) system in various brain regions. Multiple classic and/or putative neurotransmitters and neuromodulators, virtually all the peptide hormones of the endocrine and neuroendocrine systems in the brain, their specific synthesizing and hydrolyzing marker enzymes and associated uptake processes (transporters), and receptors, do not actually participate in the formation of senile plaques and neurofibrillary tangles in the brains of patients suffering from AD. The massive perturbation in different neurochemicals seen in AD is essentially caused by the ChEs-associated pathology. The graded patterns of brain ChEs expression affect the preferential vulnerability and severity of the AD clinico-pathologic presentation. It seems that the common law in nature may also dominate the destiny of brain ChEs system, i.e., the weaker the cells express AChE, the more susceptible the cells are to AD degeneration, and vice versa.

The biological behaviour and bioavailability of aluminium in man, with special reference to studies employing aluminium-26 as a tracer: review and study update

Until 1990 biokinetic studies of aluminium metabolism and biokinetics in man and other animals had been substantially inhibited by analytical and practical difficulties. Of these, the most important are the difficulties in differentiating between administered aluminium and endogenous aluminium-especially in body fluids and excreta and the problems associated with the contamination of samples with environmental aluminium. As a consequence of these it was not possible to detect small, residual body burdens of the metal following experimental administrations. Consequently, many believed aluminium to be quantitatively excreted within a short time of uptake in all, but renal-failure patients. Nevertheless, residual aluminium deposits in a number of different organs and tissues had been detected in normal subjects using a variety of techniques, including histochemical staining methods. In order to understand the origins and kinetics of such residual aluminium deposits new approaches were required. One approach taken was to employ the radioisotope (67)Ga as a surrogate, but this approach has been shown to be flawed-a consequence of the different biological behaviours of aluminium and gallium. A second arose from the availability, in about 1990, of both (26)Al-a rare and expensive isotope of aluminium-and accelerator mass spectrometry for the ultra-trace detection of this isotope. Using these techniques the basic features of aluminium biokinetics and bioavailability have been unravelled. It is now clear that some aluminium is retained in the body-most probably within the skeleton, and that some deposits in the brain. However, most aluminium that enters the blood is excreted in urine within a few days or weeks and the gastrointestinal tract provides an effective barrier to aluminium uptake. Aspects of the biokinetics and bioavailability of aluminium are described below.

Altered blood–brain barrier development in dystrophic MDX mice

In order to ascertain whether the alterations of the blood-brain barrier (BBB) seen in adult dystrophic mdx-mice [Glia 42 (2003) 235], a human model of Duchenne muscular dystrophy (DMD), are developmentally established and correlated with other dystrophin isoforms which are localized at the glial-vascular interface, we used immunocytochemistry to investigate the expression of dystrophin isoforms (Dp71) during BBB development in mdx fetuses and in adult mice. Parallelly, we used Western blot, immunocytochemistry and immunogold electron microscopy to analyze the expression of the zonula occludens (ZO-1), aquaporin-4 (AQP4) and glial fibrillary acidic (GFAP) proteins as endothelial and glial markers, and we evaluated the integrity of the mdx BBB by means of intravascular injection of horseradish peroxidase (HRP). The results show reduced dystrophin isoforms (Dp71) in the mdx mouse compared with the control, starting from early embryonic life. Endothelial ZO-1 expression was reduced, and the tight junctions were altered and unlabeled. AQP4 and GFAP glial proteins in mdx mice also showed modifications in developmental expression, the glial vascular processes being only lightly AQP4- and GFAP-labeled compared with the controls. Confocal microscopy and HRP assays confirmed the alteration in vessel glial investment, GFAP perivascular endfoot reactivity being strongly reduced and BBB permeability increasing. These results demonstrate that a reduction in dystrophin isoforms (Dp71) at glial endfeet leads to an altered development of the BBB, whose no-closure might contribute to the neurological dysfunctions associated with DMD.

Chlamydia pneumoniae infection promotes the transmigration of monocytes through human brain endothelial cells

We have investigated the effects of Chlamydia pneumoniae on human brain endothelial cells (HBMECs) and human monocytes as a mechanism for breaching the blood-brain barrier (BBB) in Alzheimer's disease (AD). HBMECs and peripheral blood monocytes may be key components in controlling the entry of C. pneumoniae into the human brain. Our results indicate that C. pneumoniae infects blood vessels and monocytes in AD brain tissues compared with normal brain tissue. C. pneumoniae infection stimulates transendothelial entry of monocytes through HBMECs. This entry is facilitated by the up-regulation of VCAM-1 and ICAM-1 on HBMECs and a corresponding increase of LFA-1, VLA-4, and MAC-1 on monocytes. C. pneumoniae infection in HBMECs and THP-1 monocytes up-regulates monocyte transmigration threefold in an in vitro brain endothelial monolayer. In this way, C. pneumoniae infection in these cell types may contribute to increased monocyte migration and promote inflammation within the CNS resulting from infection at the level of the vasculature. Thus, infection at the level of the vasculature may be a key initiating factor in the pathogenesis of neurodegenerative diseases such as sporadic AD.

Protection against hypoxia-induced increase in blood-brain barrier permeability: role of tight junction proteins and NFkappaB

Co-culture with glial cells and glia-conditioned media can induce blood-brain barrier properties in microvessel endothelial cells and protect against hypoxia-induced blood-brain barrier breakdown. We examined the effect of two types of glia-conditioned media on brain microvessel endothelial cell permeability and tight junction protein expression, and studied potential mechanisms of action. We found that C6-glioma-conditioned media, but not rat astrocyte-conditioned media, protected against an increase in permeability induced by exposure to 1% oxygen for 24 hours. This hypoxic stress caused an increase in the expression of tight junction proteins claudin-1 and actin, particularly in cells treated with C6-conditioned media. We found that C6-conditioned media has a significantly higher level of both basic fibroblast growth factor and vascular endothelial growth factor. Treatment with C6-conditioned media for 1 or 3 days protects against hypoxia-induced permeability increases, and this protective effect may be mediated by signal transduction pathways terminating at the transcription factor NFkappaB.

The reversibility of reduced cortical vein compliance in normal-pressure hydrocephalus following shunt insertion

Superficial cortical venous compression secondary to alterations in craniospinal compliance is implicated in the pathogenesis of normal pressure hydrocephalus (NPH). A reduction in the pulsation in the outflow of the cortical veins would be expected to occur following compression of these veins and this has been shown in NPH. If cortical vein compression is a causative factor in NPH, it would be expected that cortical vein compliance as measured by pulsatility would be significantly altered by a curative procedure i.e. shunt tube insertion. My purpose is to compare the blood flow pulsatility characteristics in a group of patients with NPH before and after shunt tube insertion. I initially studied 18 subjects without pathology with MRI flow quantification studies of the cerebral arteries and veins to define the range of normality. The main study involved 18 patients with idiopathic dementia and mild leukoaraiosis who served as controls and seven patients with NPH studied before and after shunt insertion. Arterial, superior sagittal and straight sinus pulsatility was not significantly different between the patients with idiopathic dementia and those NPH patients before or after shunting. Cortical vein pulsatility before shunting in the patients with NPH was 43% lower than in those with idiopathic dementia ( P=0.006). Following shunting, cortical vein pulsatility increased by 186% ( P=0.007). There is thus reduced compliance in cortical veins in NPH which is significantly increased in patients who respond to insertion of a shunt tube. These findings suggest that reversible elevation in cortical vein pressure and reversal of the normal absorption pathway for cerebrospinal fluid may be behind the pathophysiology of NPH.

Role of vascular hypoperfusion-induced oxidative stress and mitochondria failure in the pathogenesis of Azheimer disease

Chronic vascular hypoperfusion induces oxidative stress and brain energy failure, and leads to neuronal death, which manifests as cognitive impairment and the development of brain pathology as in Alzheimer disease (AD). It is becoming more widely accepted that AD is characterized by impairments in energy metabolism. We hypothesize that hypoperfusion-induced mitochondrial failure plays a central role in the generation of reactive oxygen species, resulting in oxidative damage to brain cellular compartments, especially in the vascular endothelium and neuronal cell bodies in AD. All of these changes have been found to occur before pathology and coexist during the progression of AD. In this review we have summarized recent evidence and our own knowledge regarding the relationship between the hypoperfusion-induced vascular damage that initiates oxidative stress and mitochondrial abnormalities that appear to be a key target for the development of AD pathology. Future investigations into both the mechanisms behind amyloid beta (Abeta) deposition and the possible accelerating effects of environmental factors, such as chronic hypoxia/reperfusion may open the door for effective pharmacological treatments of AD. We hypothesize that an imbalance between endothelium derived vasoconstrictors and vasodilators, along with an antioxidant system deficiency and mitochondria lesions are prominent in AD. Future studies examining the importance of mitochondrial pathophysiology in different brain cellular compartments may provide insight not only into neurodegenerative and/or cerebrovascular disease pathobiology but may also provide targets for treating these conditions.

Atherosclerotic lesions and mitochondria DNA deletions in brain microvessels as a central target for the development of human AD and AD-like pathology in aged transgenic mice

We have studied the ultrastructural features of vascular lesions and mitochondria in brain vascular wall cells from human AD brain biopsy, human short postmortem brain tissues, and yeast artificial chromosome (YAC) and C57B6/SJL transgenic positive (Tg+) mice overexpressing amyloid beta precursor protein (AbetaPP). In situ hybridization using mitochondrial DNA (mtDNA) probes for human wild type, 5 kb deleted, and mouse mtDNA was performed, along with immunocytochemistry using antibodies against amyloid precursor protein (APP), 8-hydroxy-2'-guanosine (8-OHG), and cytochrome c oxidase (COX). There was a higher degree of amyloid deposition in the vascular walls of the human AD, YAC, and C57B6/SJL Tg (+) mice compared to age-matched controls. In addition, vessels with more severe lesions showed immunopositive staining for APP and possessed large, lipid-laden vacuoles in the cytoplasm of endothelial cells (EC). Significantly more mitochondrial abnormalities were seen in human AD, YAC, and C57B6/SJL Tg (+) mouse microvessels where lesions occurred. In situ hybridization using wild and chimera (5 kb) mtDNA probes revealed positive signals in damaged mitochondria from the vascular endothelium and in perivascular cells of lesioned microvessels close to regions of large amyloid deposition. These features were absent in undamaged regions of human AD tissues, YAC and C57B6/SJL Tg (+) mouse tissues, and in age-matched control subjects. In addition, vessels with atherosclerotic lesions revealed endothelium and perivascular cells possessing clusters of wild and deleted mtDNA positive probes. These mtDNA deletions were accompanied by increased amounts of immunoreactive APP, 8-OHG, and COX in the same cellular compartment. Our observations demonstrate that vascular wall cells, especially their mitochondria, appear to be a central target for oxidative stress-induced damage.

The amyloid hypothesis: let sleeping dogmas lie?

The 'amyloid hypothesis' has guided research into Alzheimer's disease (AD) for more than a decade. A detailed review of the relevant data led us to conclude that some data, particularly those from transgenic mice, are inconsistent with the predictions of the amyloid hypothesis. Instead, most data are consistent with the notion that amyloid-beta (Abeta) peptide is neuroprotective. The majority of commentators agreed with our analysis but some were unwilling to abandon the amyloid hypothesis until the outcome of anti-Abeta therapeutic trials puts the matter beyond debate. All acknowledged that we had highlighted flaws in the amyloid hypothesis which must be addressed. To stimulate a critical reappraisal of the amyloid hypothesis we have proposed the 'bioflocculant hypothesis' which posits that Abeta serves to bind neurotoxic solutes (pathogens, proteins and metal ions) so that they can be phagocytosed and prevented from causing further damage. The hypothesis makes clear predictions that are readily falsifiable, and it has already gained credibility by predicting the recent negative outcome of Abeta vaccination trials in humans.

Endothelial cell activation is associated with cerebral white matter lesions in patients with cerebrovascular disease

Cerebral MRI scanning frequently shows white matter lesions in elderly people. They are related to cognitive impairment and may result in dementia. Although vascular risk factors are associated with the presence of white matter lesions, the exact pathogenesis remains unclear. Animal studies have indicated involvement of endothelial cells in the pathogenesis of white matter lesions and possibly dementia. We investigated the relation between endothelial cell activation and white matter lesions in individuals with cerebrovascular disease. In 29 patients with an acute stroke (n = 11) or TIAs associated with a symptomatic internal carotid artery stenosis (n = 18), markers of endothelial cell activation such as intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), sE-selectin, and sP-selectin were measured by means of ELISA. All individuals underwent 1.5-T MRI scanning. White matter lesions were rated for the periventricular and the subcortical region separately. Individuals with severe periventricular white matter lesions had higher levels of sP-selectin (245.5 ng/mL vs. 172.7 ng/mL, p = 0.01) and sVCAM-1 (547.8 ng/mL vs. 454.0 ng/mL, p = 0.04) than those without. This association was only found in individuals with a symptomatic carotid artery stenosis. No such association was found for subcortical white matter lesions. We did not detect any relation between sICAM-1 and sE-selectin and white matter lesions. Endothelial cell activation may play a role in the pathogenesis of white matter lesions, especially in periventricular white matter. Possibly, this activation represents the influence of vascular factors on the cerebral endothelium as a prelude to increasingly severe small vessel disease.

Is dopamine administration possibly a risk factor for delirium?

OBJECTIVE

We explored the possibility that the administration of intravenous dopamine increases the risk for delirium as manifested by need for haloperidol.

DESIGN

This study was based on a retrospective analysis. To examine the contribution of dopamine in the prediction of need for haloperidol, a multivariate logistic regression model was used.

SETTING

University hospital.

PATIENTS

All inpatient admissions to Stanford University Hospital over a 1-year period (n = 21,844).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Dopamine administration was associated with nearly a tripling of the odds of subsequent need of the antipsychotic drug (chi-square = 108, df = 1, p =.0001, odds ratio = 2.89), even after intensive care unit admission and diagnostic related group weight were considered as indicators of severity of illness. Even when analysis was limited to patients seen in the intensive care unit setting (n = 3,308), dopamine administration remained a very strong risk factor for haloperidol and hence possibly for delirium. The increased risk of need for haloperidol in patients administered dopamine is evident in every age group after age 20.

CONCLUSIONS

The retrospective nature of this study, the inexact method to assess acuity, and, most of all, the use of haloperidol as an indicator of the presence of delirium preclude concluding that dopamine is directly a risk factor for delirium, much less a causal risk factor. However, the association is potent enough to suggest this possibility strongly and thus supports the need for prospective studies to examine the relationship between dopamine and delirium and to consider possible prophylactic treatment against delirium in those given dopamine.

Calcium modulation of adherens and tight junction function: a potential mechanism for blood-brain barrier disruption after stroke

BACKGROUND

This review deals with the role of calcium in endothelial cell junctions of the blood-brain barrier (BBB). Calcium is critical for adherens junction function, but it appears that calcium is also important in regulating tight junction function necessary for the barrier characteristics of cerebral microvessels.

SUMMARY OF REVIEW

The BBB is critical for brain homeostasis and is located at the cerebral microvessel endothelial cells. These endothelial cells maintain their barrier characteristics via cell-cell contacts made up of adherens and tight junctions. Adherens junctions are calcium dependent; recent evidence suggests that calcium also affects tight junctions. After stroke, there is a disruption of the BBB. Interfering with calcium flux under hypoxic conditions can prevent BBB breakdown. Calcium may alter BBB junction integrity by a number of different signal transduction cascades, as well as via direct interaction of calcium ions with junction proteins. It remains to be determined whether clinical use of calcium channel antagonists is a viable means to reduce BBB disruption after stroke.

CONCLUSIONS

With the widespread use of calcium channel blockers as clinical treatments for hypertension, which is a risk factor for stroke, the exact role of calcium in modulating BBB integrity needs to be elucidated.

Vascular and neuronal effects of VEGF in the nervous system: implications for neurological disorders

Vascular endothelial growth factor (VEGF) was originally discovered as an endothelial-specific growth factor. While the predominant role of this growth factor in the formation of new blood vessels (angiogenesis) is unquestioned, recent observations indicate that VEGF also has direct effects on neurons and glial cells, and stimulates their growth, survival and axonal outgrowth. Because of these pleiotropic effects, VEGF has now been implicated in several neurological disorders both in the preterm infant (leukomalacia) and the adult (stroke, neurodegeneration, cerebral and spinal trauma, ischemic and diabetic neuropathy, nerve regeneration). A challenge for the future is to unravel to what extent the effect of VEGF in these disorders relates to its angiogenic activity or direct neurotrophic effect.

Dementia: a neuroendocrine perspective

The etiology of Alzheimer's disease (AD) has not been as yet completely defined. Genetic, environmental and neurophysiological aspects should all be taken into account. The disease has also neuroendocrine implications, some of which are discussed in this review. It is known that stress and glucocorticoids may affect neurone survival. On the contrary, some data indicate that DHEA and DHEAS exert a neuroprotective action. In AD, changes in hypothalamic-pituitary-adrenal axis function have been reported. Experimental and clinical evidence indicates that glucocorticoid hypersecretion and DHEAS levels decrement may add to hippocampal dysfunction in aging and in AD. Glucocorticoid and beta-amyloid concur in the mechanism of neurone damage, as well as excitatory amino acids (EAA), Ca++ and reactive oxygen species (ROS). The neuroprotective effects exerted by IGFs are also hindered in aging and even more in AD. Production and biological actions of IGFs are negatively influenced by cortisol hypersecretion and DHEAS decrease in patients with AD.

The role of oxidative stress in the pathophysiology of cerebrovascular lesions in Alzheimer's disease

Alzheimer's disease (AD) and stroke are two leading causes of age-associated dementia. A rapidly growing body of evidence indicates that increased oxidative stress from reactive oxygen radicals is associated with the aging process and age-related degenerative disorders such as atherosclerosis, ischemia/reperfusion, arthritis, stroke, and neurodegenerative diseases. New evidence has also indicated that vascular lesions are a key factor in the development of AD. This idea is based on a positive correlation between AD and cardiovascular and cerebrovascular diseases such as arterio- and atherosclerosis and ischemia/reperfusion injury. In this review we consider recent evidence supporting the existence of an intimate relationship between oxidative stress and vascular lesions in the pathobiology of AD. We also consider the opportunities for therapeutic interventions based on the molecular pathways involved with these causal relationships.

Immunohistochemical localization of phosphorylated glial fibrillary acidic protein in the prefrontal cortex and hippocampus from patients with schizophrenia, bipolar disorder, and depression

Increasingly, abnormalities of glial cell function have been implicated in pathological studies of the major mental illnesses (schizophrenia, bipolar disorder, and major depression). In a recent proteomic study, four isoforms of astrocytic glial fibrillary acidic protein (GFAP) were decreased in one or more of these diseases. In the current study, we sought to determine the immunohistochemical localization of phosphorylated GFAP (pGFAP) in the prefrontal cortex and hippocampus and to describe possible disease-related changes in the distribution of pGFAP containing astrocytes. In the prefrontal cortex, interlaminar astrocytes in layer I and stellate astrocytes in layers II and VI were labeled. Labeled cells were also present adjacent to blood vessels in the gyral white matter and in underlying white matter generally. In the hippocampus, labeled cells were present in the polymorphic layer of the dentate gyrus. In the prefrontal cortex, schizophrenia and major depression were characterized by decreased labeling of astrocytes adjacent to blood vessels. There were no significant differences between the diagnostic groups in the other prefrontal layers or in the hippocampus. These results suggest that reduced numbers or functional regulation of pGFAP containing astrocytes occurs in schizophrenia and major depression. The mechanism by which this deficit occurs is not known, but it may adversely effect the regulation of neuronal metabolism, communication, and response to injury.

Involvement of cerebrovascular semicarbazide-sensitive amine oxidase in the pathogenesis of Alzheimer's disease and vascular dementia

Fibrillary tangles and senile plaques resulting from advanced aggregation of beta-amyloid and other proteins are pathological characteristics of Alzheimer's disease (AD). Cerebral amyloid angiopathy is quite common in AD. In fact, amyloid fibrils fuse to and emanate from the vascular basement membrane. Semicarbazide-sensitive amine oxidase (SSAO), located in outer membranes of vascular smooth muscles and endothelia, catalyzes deamination of methylamine-producing formaldehyde and hydrogen peroxide. SSAO is also involved in lymphocyte adhesion and is up-regulated in response to inflammation. SSAO-mediated generation of formaldehyde can induce protein (i.e. beta-amyloid) cross-linkage, deposition and subsequently plaque formation in the compartment adjacent to the cerebrovessels. Formaldehyde may cause cytotoxicity, which induces inflammation and release of more SSAO, producing a cascade of toxic cycle. Increased SSAO-mediated reaction may be chronically involved in the pathogenesis of vascular dementia and AD.

Expression of mutant amyloid precursor proteins decreases adhesion and delays differentiation of Hep-1 cells

The amyloid precursor protein (APP) is a type I integral membrane protein and is processed to generate several intra-cellular and secreted fragments. The physiological role of APP and its processed fragments is unclear. Several mutations have been discovered in APP, which are causative of early-onset, familial, neurological disease, including Alzheimer's disease (FAD). These mutations alter the processing of APP and lead to excess production and extra-cellular deposition of A-beta peptide (Abeta). We have examined the role of APP in a cell culture model of endothelial cell function. The endothelial cell line, Hep-1, was stably transfected with wild-type (wt) and FAD mutant forms of APP (mAPP). Secretion of sAPPalpha was reduced in cell lines over-expressing mAPP when these cells were grown on several different substrates. Levels of secreted Abeta were increased as measured by ELISA in the mutant cell lines. Cell adhesion to laminin-, fibronectin-, collagen I-, and collagen IV-coated culture flasks was reduced in all mAPP-expressing cell lines, while in lines over-expressing wt-APP, adhesiveness was slightly increased. Cell lines over-expressing mAPP differentiated more slowly into capillary network-like structures on Matrigel than those expressing wt-APP. No differences were detected among all cell lines in a migration/invasion assay. The results suggest that APP may have a role in cell adhesiveness and maturation of endothelial cells into capillary-like networks. The reduction in adhesion and differentiation in mutant cell lines may be due to reduced amounts of sAPPalpha released into the culture media or toxic effects of increased extracellular Abeta.

Exogenous A beta1-40 reproduces cerebrovascular alterations resulting from amyloid precursor protein overexpression in mice

Transgenic mice overexpressing the amyloid precursor protein (APP) have a profound impairment in endothelium-dependent cerebrovascular responses that is counteracted by the superoxide scavenger superoxide dismutase (SOD). The authors investigated whether the amyloid-beta peptide (A beta) is responsible for the cerebrovascular effects of APP overexpression. Cerebral blood flow (CBF) was monitored by a laser-Doppler flowmeter in anesthetized-ventilated mice equipped with a cranial window. Superfusion of A beta1-40 on the neocortex reduced resting CBF in a dose-dependent fashion (-29% +/- 7% at 5 micromol/L) and attenuated the increase in CBF produced by the endothelium-dependent vasodilators acetylcholine (-41% +/- 8%), bradykinin (-39% +/- 9%), and the calcium ionophore A23187 (-37% +/- 5%). A beta1-40 did not influence the CBF increases produced by the endothelium-independent vasodilators S-nitroso-N-acetylpenicillamine and hypercapnia. In contrast, A beta1-42 did not attenuate resting CBF or the CBF increases produced by endothelium-dependent vasodilators. Cerebrovascular effects of A beta1-40 were reversed by the superoxide scavengers SOD or MnTBAP. Furthermore, substitution of methionine 35 with norleucine, a mutation that blocks the ability of A beta to generate reactive oxygen species, abolished A beta1-40 vasoactivity. The authors conclude that A beta1-40, but not A beta1-42, reproduces the cerebrovascular alterations observed in APP transgenics. Thus, A beta1-40 could play a role in the cerebrovascular alterations observed in Alzheimer's dementia.