Alzheimer Blood-brain Barrier Research Articles

Reconsidering the role of blood-brain barrier in Alzheimer's disease: From delivery to target.

The existence of a selective blood-brain barrier (BBB) and neurovascular coupling are two unique central nervous system vasculature features that result in an intimate relationship between neurons, glia, and blood vessels. This leads to a significant pathophysiological overlap between neurodegenerative and cerebrovascular diseases. Alzheimer's disease (AD) is the most prevalent neurodegenerative disease whose pathogenesis is still to be unveiled but has mostly been explored under the light of the amyloid-cascade hypothesis. Either as a trigger, bystander, or consequence of neurodegeneration, vascular dysfunction is an early component of the pathological conundrum of AD. The anatomical and functional substrate of this neurovascular degeneration is the BBB, a dynamic and semi-permeable interface between blood and the central nervous system that has consistently been shown to be defective. Several molecular and genetic changes have been demonstrated to mediate vascular dysfunction and BBB disruption in AD. The isoform ε4 of Apolipoprotein E is at the same time the strongest genetic risk factor for AD and a known promoter of BBB dysfunction. Low-density lipoprotein receptor-related protein 1 (LRP-1), P-glycoprotein, and receptor for advanced glycation end products (RAGE) are examples of BBB transporters implicated in its pathogenesis due to their role in the trafficking of amyloid-β. This disease is currently devoid of strategies that change the natural course of this burdening illness. This unsuccess may partly be explained by our misunderstanding of the disease pathogenesis and our inability to develop drugs that are effectively delivered to the brain. BBB may represent a therapeutic opportunity as a target itself or as a therapeutic vehicle. In this review, we aim to explore the role of BBB in the pathogenesis of AD including the genetic background and detail how it can be targeted in future therapeutic research.

O‐GlcNAcylation modulates GLUT1 levels at the blood‐brain barrier

AbstractBackgroundGlucose transporter 1 (GLUT1) at the blood‐brain barrier (BBB) is essential for glucose uptake into the brain. Previous studies have shown that GLUT1 levels are reduced at the BBB in Alzheimer’s disease (AD) post‐mortem brain, and perhaps explains the decreased glucose utilization observed in AD (Sweeney et al., Nat Rev Neurol, 2018). Individuals with a genetic reduction of GLUT1, known as GLUT1‐deficiency syndrome, were treated with increased blood glucose with no long‐lasting increase in brain glucose. Diabetes is a risk factor for AD and AD is sometimes referred to as Type‐3 diabetes due to elevated blood glucose levels. Taken together, these ideas provoked us to investigate connections between glucose and GLUT1 levels. Here, we tested if the glucose‐dependent post‐translational modification, O‐linked‐N‐acetylglucosaminylation (O‐GlcNAcylation), is the missing link. We hypothesized that increasing glucose concentrations will elevate O‐GlcNAcylation and decrease GLUT1 levels at the BBB. Furthermore, previous studies have shown that decreased GLUT1 levels result in reduced levels of the low‐density lipoprotein receptor‐related protein‐1 (LRP‐1) (Winkler, Nat Neurosci, 2015). Thus, we also are determining if altering glucose levels not only changes GLUT1 levels, but also other key BBB receptors implicated in AD.MethodsMouse brain endothelial (bEnd.3) cells were treated with vehicle (glucose 5.6 mmol), DMSO, the O‐GlcNAcase inhibitor Thiamet‐G (TMG, 1 µM), or the O‐GlcNAc transferase inhibitor OSMI‐1 (20 µM), for 24 and 48 hours. Next, the protein expression of O‐GlcNAc and GLUT1 were measured by western blot.ResultsAs previously reported, TMG increased and OSMI‐1 decreased O‐GlcNAcylation at both 24 and 48 h, compared to vehicle. Notably, TMG treatment significantly reduced and OSMI‐1 increased GLUT1 expression at both time points.ConclusionGLUT1 levels are modulated through O‐GlcNAcylation at BBB. When blood glucose levels are high, O‐GlcNAcylation will be high, thereby reducing GLUT1 at the BBB and brain glucose uptake. This is likely a homeostatic mechanism to prevent spikes in brain glucose levels when blood sugar levels are elevated.

Lifestyle impacts on insulin transport at the blood‐brain barrier in mice

AbstractBackgroundThe blood‐brain barrier (BBB) is a regulatory interface, controlling the blood‐to‐brain transport of many substances, resulting in nutrient delivery to the central nervous system (CNS) and communication between the periphery and CNS. There are structural and functional changes within the BBB in Alzheimer’s disease, which may contribute to the detrimental effects occurring within the CNS. CNS insulin resistance is one of many detrimental features of Alzheimer’s disease. As the BBB is responsible for the delivery of insulin to the CNS, alterations in insulin BBB transport could be a cause of CNS insulin resistance. Indeed, various lifestyle factors are known to impact insulin BBB pharmacokinetics, including diet and exercise, which have also been shown to impact Alzheimer’s disease progression.MethodsUtilizing sensitive radiotracer methods of substrate transport at the BBB in young male and female mice, we investigated the impact of exposure to a voluntary running wheel and what role CNS insulin resistance has on insulin BBB pharmacokinetics.ResultsAcute exercise increased insulin BBB transport and CNS insulin resistance decreased insulin brain uptake.ConclusionCNS insulin resistance decreases insulin BBB transport in mice, particularly in females. We found a lifestyle intervention, such as exercise, is able to enhance insulin BBB transport, which may be able to attenuate CNS insulin resistance. Future work is necessary to determine if exercise can reverse the insulin BBB transport deficiencies observed due to CNS insulin resistance.

The Impairment of Blood-Brain Barrier in Alzheimer's Disease: Challenges and Opportunities with Stem Cells.

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and its prevalence is increasing. Nowadays, very few drugs effectively reduce AD symptoms and thus, a better understanding of its pathophysiology is vital to design new effective schemes. Presymptomatic neuronal damage caused by the accumulation of Amyloid β peptide and Tau protein abnormalities remains a challenge, despite recent efforts in drug development. Importantly, therapeutic targets, biomarkers, and diagnostic techniques have emerged to detect and treat AD. Of note, the compromised blood-brain barrier (BBB) and peripheral inflammation in AD are becoming more evident, being harmful factors that contribute to the development of the disease. Perspectives from different pre-clinical and clinical studies link peripheral inflammation with the onset and progression of AD. This review aims to analyze the main factors and the contribution of impaired BBB in AD development. Additionally, we describe the potential therapeutic strategies using stem cells for AD treatment.

Upregulation of ribosome complexes at the blood-brain barrier in Alzheimer's disease patients

The cerebrovascular-specific molecular mechanism in Alzheimer’s disease (AD) was investigated by employing comprehensive and accurate quantitative proteomics. Highly purified brain capillaries were isolated from cerebral gray and white matter of four AD and three control donors, and examined by SWATH (sequential window acquisition of all theoretical fragment ion spectra) proteomics. Of the 29 ribosomal proteins that were quantified, 28 (RPLP0, RPL4, RPL6, RPL7A, RPL8, RPL10A, RPL11, RPL12, RPL14, RPL15, RPL18, RPL23, RPL27, RPL27A, RPL31, RPL35A, RPS2, RPS3, RPS3A, RPS4X, RPS7, RPS8, RPS14, RPS16, RPS20, RPS24, RPS25, and RPSA) were significantly upregulated in AD patients. This upregulation of ribosomal protein expression occurred only in brain capillaries and not in brain parenchyma. The protein expression of protein processing and N-glycosylation-related proteins in the endoplasmic reticulum (DDOST, STT3A, MOGS, GANAB, RPN1, RPN2, SEC61B, UGGT1, LMAN2, and SSR4) were also upregulated in AD brain capillaries and was correlated with the expression of ribosomal proteins. The findings reported herein indicate that the ribosome complex, the subsequent protein processing and N-glycosylation-related processes are significantly and specifically upregulated in the brain capillaries of AD patients.

A sporadic Alzheimer's blood-brain barrier model for developing ultrasound-mediated delivery of Aducanumab and anti-Tau antibodies.

Rationale: The blood-brain barrier (BBB) is a major impediment to therapeutic intracranial drug delivery for the treatment of neurodegenerative diseases, including Alzheimer's disease (AD). Focused ultrasound applied together with microbubbles (FUS+MB) is a novel technique to transiently open the BBB and increase drug delivery. Evidence suggests that FUS+MB is safe, however, the effects of FUS+MB on human BBB cells, especially in the context of AD, remain sparsely investigated. In addition, there currently are no cell platforms to test for FUS+MB-mediated drug delivery.Methods: Here we generated BBB cells (induced brain endothelial-like cells (iBECs) and astrocytes (iAstrocytes)) from apolipoprotein E gene allele E4 (APOE4, high sporadic AD risk) and allele E3 (APOE3, lower AD risk) carrying patient-derived induced pluripotent stem cells (iPSCs). We established mono- and co-culture models of human sporadic AD and control BBB cells to investigate the effects of FUS+MB on BBB cell phenotype and to screen for the delivery of two potentially therapeutic AD antibodies, an Aducanumab-analogue (AduhelmTM; anti-amyloid-β) and a novel anti-Tau antibody, RNF5. We then developed a novel hydrogel-based 2.5D BBB model as a step towards a more physiologically relevant FUS+MB drug delivery platform.Results: When compared to untreated cells, the delivery of Aducanumab-analogue and RNF5 was significantly increased (up to 1.73 fold), across the Transwell-based BBB models following FUS+MB treatment. Our results also demonstrated the safety of FUS+MB indicated by minimal changes in iBEC transcriptome as well as little or no changes in iBEC or iAstrocyte viability and inflammatory responses within the first 24 h post FUS+MB. Furthermore, we demonstrated successful iBEC barrier formation in our novel 2.5D hydrogel-based BBB model with significantly increased delivery (1.4 fold) of Aducanumab-analogue following FUS+MB.Conclusion: Our results demonstrate a robust and reproducible approach to utilize patient cells for FUS+MB-mediated drug delivery screening in vitro. With such a cell platform for FUS+MB research previously not reported, it has the potential to identify novel FUS+MB-deliverable drugs as well as screen for cell- and patient-specific effects of FUS+MB, accelerating the use of FUS+MB as a therapeutic modality in AD.

Effects of on behavior and blood-brain barrier in Alzheimer's disease mice.

To investigate the effects of on behavior and blood brain barrier (BBB) in Alzheimer's disease mice. Thirty-eight 4-month-old APP/PS1 double transgenic mice were randomly divided into three groups: model group, low-dose group and high-dose group. Saline, and 12 g·kg·d were given to each group by continuous gavage once a day for respectively. The changes in activities of daily live and fear conditioning memory behavior of mice were examined by nesting behavior test and fear conditioning test, respectively. The β-amyloid protein (Aβ) depositions in cortex and hippocampal CA1 area of mice were detected by thioflavin T staining. The CD34 and activities fibrinogen (Fib) immunofluorescence double staining were used to determine the vascular endothelial integrity and BBB exudation. Compared with model mice, activities of daily live were significantly improved in low-dose and high-dose groups (both <0.01), the fear memory ability was significantly increased in high-dose group (<0.01). The amount of Aβ deposition in cortex and hippocampal CA1 decreased significantly in high-dose group, the area ratio decreased significantly; the area ratio of Aβ deposition in hippocampal CA1 region in low-dose group also decreased (all <0.05). The proportions of CD34 positive area of cortex in low and high dose groups increased, the percentage of fibrinogen positive area decreased (all <0.05). The proportion of CD34 positive area in hippocampal CA1 region in high-dose group was significantly increased, the percentage of fibrinogen positive area decreased significantly (both <0.05). especially high-dose can improve the activities of daily live and fear conditioning memory function of APP/PS1 mice, reduce the deposition of Aβ in brain. The mechanism may be related to the reduction of BBB permeability and the protection of the integrity of BBB.

Effect of High Cholesterol Regulation of LRP1 and RAGE on Aβ Transport Across the Blood-Brain Barrier in Alzheimer's Disease.

High cholesterol aggravates the risk development of Alzheimer's disease (AD). AD is closely related to the transport impairment of Amyloid-β (Aβ) in the blood-brain barrier. It is unclear whether high cholesterol affects the risk of cognitive impairment in AD by affecting Aβ transport. The purpose of the study is to investigate whether high cholesterol regulates Aβ transport through low-density Lipoprotein Receptor-Related Protein 1 (LRP1) and Receptor for Advanced Glycation End products (RAGE) in the risk development of AD. We established high cholesterol AD mice model. The learning and memory functions were evaluated by Morris Water Maze (MWM). Cerebral microvascular endothelial cells were isolated, cultured, and observed. The expression levels of LRP1 and RAGE of endothelial cells and their effect on Aβ transport in vivo were observed. The expression level of LRP1 and RAGE was detected in cultured microvessels after using Wnt inhibitor DKK-1 and β-catenin inhibitor XAV-939. Hypercholesterolemia exacerbated spatial learning and memory impairment. Hypercholesterolemia increased serum Aβ40 level, while serum Aβ42 level did not change significantly. Hypercholesterolemia decreased LRP1 expression and increased RAGE expression in cerebral microvascular endothelial cells. Hypercholesterolemia increased brain apoptosis in AD mice. In in vitro experiment, high cholesterol decreased LRP1 expression and increased RAGE expression, increased Aβ40 expression in cerebral microvascular endothelial cells. High cholesterol regulated the expressions of LRP1 and RAGE and transcriptional activity of LRP1 and RAGE promoters by the Wnt/β-catenin signaling pathway. High cholesterol decreased LRP1 expression and increased RAGE expression in cerebral microvascular endothelial cells, which led to Aβ transport disorder in the blood-brain barrier. Increased Aβ deposition in the brain aggravated apoptosis in the brain, resulting to cognitive impairment of AD mice.

Effects of moxibustion on the structure and function of blood brain barrier in Alzheimer's disease model rats

To investigate the effects of moxibustion on the structure and function of blood-brain barrier in Alzheimer's disease (AD) model rats. Forty-eight SD rats were randomly divided into 4 groups: normal control group, sham operation group, model group, moxibustion group. Model group and moxibustion group rats were injected with aggregated Aβ25-35 by bilateral hippocampus. In the rat model, the sham-operated group was injected with the same amount of normal saline in the bilateral hippocampus, and the normal group was not treated. After successful modeling, the moxibustion treatment was given at 2～3 cm above the Baihui, Shenshu and Yintang points of the moxibustion group rats, each time for 10 min, once a day, continuous treatment for 21 d. The Morris water maze test was used to evaluate the learning and memory ability of rats in each group. The Evans blue method was used to detect the permeability of blood-brain barrier. The ultrastructure of blood-brain barrier was observed under electron microscope. The matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) positive cells in hippocampus were detected by immunohistochemistry. Compared with the sham operation group, the escape latency was significantly increased (P＜0.01), and the space exploration time was decreased (P＜0.01), the learning and memory function in model group was impaired seriously, the Evans blue content in the brain was increased significantly (P＜0.01), the perivascular edema became larger, and the blood-brain barrier structure function was impaired. At the same time, the positive expressions of MMP-2 and MMP-9 in hippocampus were increased significantly (P＜0.01). Compared with model group, the learning and memory ability in moxibustion group rats was enhanced (P＜ 0.05), the content of Evans blue in the brain was decreased (P＜0.05), the degree of perivascular edema was reduced, and the damage of blood-brain barrier was improved. Positive expressions of MMP-2 and MMP-9 in hippocampus were decreased (P＜0.05 or P＜ 0.01). Moxibustion can decrease the expressions of MMP-2 and MMP-9, and reduce the damage of the structure and function of blood-brain barrier, thereby improving the learning and memory ability of AD model rats, and exerting therapeutic effects.

Autoregulated paracellular clearance of amyloid-β across the blood-brain barrier.

The blood-brain barrier (BBB) is essential for maintaining brain homeostasis and protecting neural tissue from damaging blood-borne agents. The barrier is characterized by endothelial tight junctions that limit passive paracellular diffusion of polar solutes and macromolecules from blood to brain. Decreased brain clearance of the neurotoxic amyloid-β (Aβ) peptide is a central event in the pathogenesis of Alzheimer's disease (AD). Whereas transport of Aβ across the BBB can occur via transcellular endothelial receptors, the paracellular movement of Aβ has not been described. We show that soluble human Aβ(1-40) monomers can diffuse across the paracellular pathway of the BBB in tandem with a decrease in the tight junction proteins claudin-5 and occludin in the cerebral vascular endothelium. In a murine model of AD (Tg2576), plasma Aβ(1-40) levels were significantly increased, brain Aβ(1-40) levels were decreased, and cognitive function was enhanced when both claudin-5 and occludin were suppressed. Furthermore, Aβ can cause a transient down-regulation of claudin-5 and occludin, allowing for its own paracellular clearance across the BBB. Our results show, for the first time, the involvement of the paracellular pathway in autoregulated Aβ movement across the BBB and identify both claudin-5 and occludin as potential therapeutic targets for AD. These findings also indicate that controlled modulation of tight junction components at the BBB can enhance the clearance of Aβ from the brain.

Targeted Drug Delivery Across the Blood Brain Barrier in Alzheimer’s Disease

The discovery of drugs for Alzheimer's disease (AD) therapy that can also permeate the blood brain barrier (BBB) is very difficult owing to its specificity and restrictive nature. The BBB disruption or the administration of the drug directly into the brain is not an option due to toxic effects and low diffusion of the therapeutic molecule in the brain parenchyma. A promising approach for drug systemic delivery to the central nervous system is the use of nanosized carriers. The therapeutic potential of certain nanopharmaceuticals for AD has already been demonstrated in vivo after systemic delivery. They are based on i) conjugates of drug and monoclonal antibodies against BBB endogenous receptors; ii) cationized or end terminal protected proteins/peptides; iii) liposomes and polymeric nanoparticles coated with polysorbate 80, cationic macromolecules or antibodies against BBB receptors/amyloid beta-peptides. Optimization and further validation of these systems are needed.

The potential mechanisms of Aβ-receptor for advanced glycation end-products interaction disrupting tight junctions of the blood-brain barrier in Alzheimer's disease

The receptor for advanced glycation end-products (RAGE) is a multiligand membrane receptor that has been implicated in the cytotoxicity effects of β-amyloid protein (Aβ) in AD. Positive feedback mechanism of RAGE within blood-brain barrier (BBB) and/or cells inside the brain is proposed, including interaction with Aβ stimulating activation of proinflammatory cytokines, release of reactive oxygen species (ROS), which leads to neuron damage and BBB dysfunction. RAGE is the main factor mediating Aβ cytotoxicity. Attenuation of RAGE activity may inhibit Aβ from accumulation in the cerebral blood vessels and prevent neurotoxicity. Furthermore, RAGE may serve as a therapeutic target for Alzheimer's disease by inhibiting pathophysiological consequences of Aβ-RAGE interaction. Tight junctions (TJ) are identified as the basic structure of the BBB and RAGE-mediated Aβ cytotoxicity to the brain microvascular endothelial cells (BMEC), resulting in damaged BBB structural integrity. However, the potential mechanism is poorly studied.

The blood-brain barrier in Alzheimer's disease

The blood-brain barrier in Alzheimer's disease

F5‐01‐01: The Blood‐brain barrier in Alzheimer's disease

F5‐01‐01: The Blood‐brain barrier in Alzheimer's disease

Protection of the Blood-Brain Barrier by Pentosan Against Amyloid-β-Induced Toxicity

Endothelial cells of brain capillaries forming the blood-brain barrier play an important role in the pathogenesis and therapy of Alzheimer's disease. Amyloid-β (Aβ) peptides are key pathological elements in the development of the disease. A blood-brain barrier model, based on primary rat brain endothelial cells was used in which the barrier properties were induced by glial cells. The effects of amyloid peptides have been tested on cell viability and barrier functions. Aβ showed toxic effects on primary rat brain endothelial cells measured by MTT dye conversion and the lactate dehydrogenase release. Morphologically cytoplasmic vacuolization, disruption of the structure of cytoplasmic organelles and tight junctions could be observed in brain endothelial cells. Treatment with Aβ1-42 decreased the electrical resistance, and increased the permeability of brain endothelial cell monolayers for both fluorescein and albumin. Serum amyloid P component which stabilizes Aβ fibrils in cortical amyloid plaques and cerebrovascular amyloid deposits significantly potentiated the barrier-weakening effect of Aβ1-42. Sulfated polysaccharide pentosan could decrease the toxic effects of Aβ peptides in brain endothelial cells. It could also significantly protect the barrier integrity of monolayers from damaging actions of peptides. Pentosan modified the size, and significantly decreased the number of amyloid aggregates demonstrated by atomic force microscopy. The present data further support the toxic effects of amyloid peptides on brain endothelial cells, and can contribute to the development of molecules protecting the blood-brain barrier in Alzheimer's disease.

Transport of Drugs Across the blood–brain Barrier in Alzheimer‘s Disease

Alzheimer's disease, a neurodegenerative disorder, is associated with various pathological alterations to the blood-brain barrier, including disruption to the inter-endothelial tight junction proteins, altered expression of transport proteins involved in drug efflux, a reduction in cerebral blood flow and a thickening of the brain capillary basement membrane. There are many conflicting reports on whether such changes alter the ability of endogenous proteins to extravasate into the brain parenchyma, and there are even fewer reports focusing on the potential impact of these changes on drug transport into the CNS. The purpose of this review is to critically evaluate how the reported changes to the blood-brain barrier in Alzheimer's disease have (or have not) resulted in altered CNS drug delivery, and to highlight the requirement for more rigorous and systematic studies in this field for the benefit of drug discovery and delivery scientists.

Blood-Brain Barrier Permeability Correlates with Medial Temporal Lobe Atrophy but Not with Amyloid-β Protein Transport across the Blood-Brain Barrier in Alzheimer’s Disease

Background/Aims: Alterations in the blood-brain barrier (BBB) may play an important role in the pathogenesis and treatment of Alzheimer’s disease (AD). We investigated BBB disturbance and its influence on the equilibrium of amyloid-β protein (Aβ) between plasma and cerebrospinal fluid (CSF) in AD patients. Methods: We analyzed albumin ratio as a marker of the BBB permeability and correlated it with the severity of dementia, brain atrophy on MRI, apolipoprotein E isoform, CSF levels of total tau, CSF and plasma levels of Aβ 1–40 (Aβ₄₀) and 1–42 (Aβ₄₂), and CSF/plasma ratios of Aβ₄₀ and Aβ₄₂ in 42 AD patients. Results: The albumin ratio was positively correlated with the severity of medial temporal lobe atrophy but not with the other parameters including CSF/plasma ratios of Aβ₄₀ or Aβ₄₂. Conclusion: Our results suggest that progression of medial temporal lobe atrophy is associated with increased BBB permeability and that the transport of Aβ across the BBB is not influenced by the BBB alteration in AD.

Guarding the Blood–Brain Barrier: A Role for Estrogen in the Etiology of Neurodegenerative Disease

Although the effect of estrogen replacement therapy on the incidence of the neurodegenerative disease such as Alzheimer's disease is controversial, experimental studies indicate that estrogen replacement to young adult animals is neuroprotective and that perimenopausal estrogen replacement is associated with a decreased incidence of Alzheimer's disease. Estrogen affects a wide variety of cellular processes that can protect neuronal health. This article considers the disruption of the blood-brain barrier in Alzheimer's disease and forwards the hypothesis that estrogen may preserve neural health by maintaining the integrity of the blood-brain barrier.

Serum protein leakage in Alzheimer's disease revisited.

Leakage of serum proteins into the brain parenchyma has been repeatedly used as evidence of blood-brain barrier (BBB) damage in experimental and human studies. However, there is no consensus in the literature concerning this phenomenon in Alzheimer's disease (AD). We have examined this question by comparing frontal lobe sections in seven groups of patients: Multi-infarct dementia (n = 6), AD with (n = 10) and without (n = 10) infarcts, age-matched controls with (n = 10) and without (n = 10) infarcts, controls with neurodegenerative diseases other than AD, and young controls (n = 10). An additional series compared prospectively followed patients with a diagnosis of either multi-infarct dementia (n = 5) or AD (n = 4). Albumin was detected in white-matter astrocytes in all cases, without significant variation in intensity. In addition, diverse combinations of neurons, astrocytes, and (in AD patients) senile plaques were present in the cerebral cortex in an inconsistent manner. Semiquantitative analysis showed no statistically significant differences among groups. Anti-IgG labeled astrocytes in infarcts only. Complement C3c component was detected in rare amyloid plaques in a minority (15%) of AD cases. Selective labeling of AD-specific lesions in a patchy manner was observed for serum amyloid P. We conclude that there is no immunohistochemical evidence of alteration of the BBB in Alzheimer's disease with or without vascular factors or in old age. Serum amyloid P binds avidly to AD lesions, but our findings are consistent with leakage through the BBB during the agonal or immediate postmortem period. Finally, no specific pattern of abnormality in the BBB was detected in multi-infarct dementia.

Cerebral microvessels in Alzheimer's have reduced protein kinase C activity

Protein kinase C (PKC) is an important intracellular signalling enzyme. Numerous studies have suggested that alterations in this enzyme occur in aging and dementia. The objective of this study was to examine PKC in the cerebral microcirculation in aging and Alzheimer's disease. PKC activity, amount, and isoform distribution were analyzed in microvessels from adult and aged rodents as well as from Alzheimer patients and nondemented elderly controls. PKC activity was lower in Alzheimer vessels than in vessels from control brains, despite the presence of similar levels of PKC enzyme. In contrast, both activity and enzyme levels in young and aged rats were comparable. The β-isoform was present in both rat and human microvessels and there were no age- or disease-related alterations. The loss in activity in cerebromicrovascular PKC in Alzheimer's suggest that perturbations in phosphorylation signalling cascades may exist at the Alzheimer blood-brain barrier.