Amyloid beta peptide alters intracellular vesicle trafficking and cholesterol homeostasis

Sigma-2 receptor modulator CT1812 alters key pathways and rescues retinal pigment epithelium (RPE) functional deficits associated with dry age-related macular degeneration (AMD)

Trafficking defects in retinal pigmented epithelial (RPE) cells contribute to RPE atrophy, a hallmark of geographic atrophy (GA) in dry age-related macular degeneration (AMD). Dry AMD pathogenesis is multifactorial, including amyloid-β (Aβ) accumulation and oxidative stress-common features of Alzheimer's disease (AD). The Sigma-2 receptor (S2R) regulates lipid and protein trafficking, and S2R modulators reverse trafficking deficits in neurodegeneration in vitro models. Given overlapping mechanisms contributing to AD and AMD, S2R modulator effects on RPE function were investigated. The S2R modulator CT1812 is in clinical trials for AD, dementia with Lewy bodies, and GA. Leveraging AD trials testing CT1812, unbiased analyses of patient biofluid proteomes revealed that proteins altered by CT1812 associated with GA and macular degeneration disease ontologies and overlapped with proteins altered in dry AMD. Differential expression analysis of RPE transcripts from APP-Swedish/London mutant transgenic mice, a model featuring Aβ accumulation, revealed reversal of autophagy/trafficking transcripts in S2R modulator-treated animals versus vehicle toward healthy control levels. Photoreceptor outer segment (POS) trafficking in human RPE cells showed deficits in response to Aβ1-42 or hydrogen peroxide compared to vehicle. S2R modulators normalized stressor-induced POS trafficking deficits, resembling healthy control. Taken together, S2R modulation may provide a novel therapeutic strategy for dry AMD.

Single-Cell MTT: A Simple and Sensitive Assay for Determining the Viability and Metabolic Activity of Polyploid Giant Cancer Cells (PGCCs)

Solid tumors and tumor-derived cell lines commonly contain highly enlarged (giant) cancer cells that enter a state of transient dormancy (active sleep) after they are formed, but retain viability, secrete growth promoting factors, and exhibit the ability to generate rapidly proliferating progeny with stem cell-like properties. Giant cells with a highly enlarged nucleus or multiple nuclei are often called polyploid giant cancer cells (PGCCs). Although PGCCs constitute only a subset of cells within a solid tumor/tumor-derived cell line, their frequency can increase markedly following exposure to ionizing radiation or chemotherapeutic drugs. In this chapter we outline a simple and yet highly sensitive cell-based assay, called single-cell MTT, that we have optimized for determining the viability and metabolic activity of PGCCs before and after exposure to anticancer agents. The assay measures the ability of individual PGCCs to convert the MTT tetrazolium salt to its water insoluble formazan metabolite. In addition to evaluating PGCCs, this assay is also a powerful tool for determining the viability and metabolic activity of cancer cells undergoing premature senescence following treatment with anticancer agents, as well as for distinguishing dead cancer cells and dying cells (e.g., exhibiting features of apoptosis, ferroptosis, etc.) that have the potential to resume proliferation through a process called anastasis.

Effects of Sex, Age, and Apolipoprotein E Genotype on Brain Ceramides and Sphingosine-1-Phosphate in Alzheimer's Disease and Control Mice

Apolipoprotein ε4 (APOE)4 is a strong risk factor for the development of Alzheimer’s disease (AD) and aberrant sphingolipid levels have been implicated in AD. We tested the hypothesis that the APOE4 genotype affects brain sphingolipid levels in AD. Seven ceramides and sphingosine-1-phosphate (S1P) were quantified by LC-MSMS in hippocampus, cortex, cerebellum, and plasma of <3 months and >5 months old human APOE3 and APOE4-targeted replacement mice with or without the familial AD (FAD) background of both sexes (145 animals). APOE4 mice had higher Cer(d18:1/24:0) levels in the cortex (1.7-fold, p = 0.002) than APOE3 mice. Mice with AD background showed higher levels of Cer(d18:1/24:1) in the cortex than mice without (1.4-fold, p = 0.003). S1P levels were higher in all three brain regions of older mice than of young mice (1.7-1.8-fold, all p ≤ 0.001). In female mice, S1P levels in hippocampus (r = −0.54 [−0.70, −0.35], p < 0.001) and in cortex correlated with those in plasma (r = −0.53 [−0.71, −0.32], p < 0.001). Ceramide levels were lower in the hippocampus (3.7–10.7-fold, all p < 0.001), but higher in the cortex (2.3–12.8-fold, p < 0.001) of female than male mice. In cerebellum and plasma, sex effects on individual ceramides depended on acyl chain length (9.5-fold lower to 11.5-fold higher, p ≤ 0.001). In conclusion, sex is a stronger determinant of brain ceramide levels in mice than APOE genotype, AD background, or age. Whether these differences impact AD neuropathology in men and women remains to be investigated.

Preclinical and clinical biomarker studies of CT1812: A novel approach to Alzheimer's disease modification

INTRODUCTION

Amyloid beta (Aβ) oligomers are one of the most toxic structural forms of the Aβ protein and are hypothesized to cause synaptotoxicity and memory failure as they build up in Alzheimer's disease (AD) patients' brain tissue. We previously demonstrated that antagonists of the sigma-2 receptor complex effectively block Aβ oligomer toxicity. CT1812 is an orally bioavailable, brain penetrant small molecule antagonist of the sigma-2 receptor complex that appears safe and well tolerated in healthy elderly volunteers. We tested CT1812's effect on Aβ oligomer pathobiology in preclinical AD models and evaluated CT1812's impact on cerebrospinal fluid (CSF) protein biomarkers in mild to moderate AD patients in a clinical trial (ClinicalTrials.gov NCT02907567).

METHODS

Experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer binding to synapses in vitro, to human AD patient post mortem brain tissue ex vivo, and in living APP_Swe /PS1dE9 transgenic mice in vivo. Additional experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer-induced deficits in membrane trafficking rate, synapse number, and protein expression in mature hippocampal/cortical neurons in vitro. The impact of CT1812 on cognitive function was measured in transgenic Thy1 huAPP^Swe/Lnd+ and wild-type littermates. A multicenter, double-blind, placebo-controlled parallel group trial was performed to evaluate the safety, tolerability, and impact on protein biomarker expression of CT1812 or placebo given once daily for 28 days to AD patients (Mini-Mental State Examination 18-26). CSF protein expression was measured by liquid chromatography with tandem mass spectrometry or enzyme-linked immunosorbent assay in samples drawn prior to dosing (Day 0) and at end of dosing (Day 28) and compared within each patient and between pooled treated versus placebo-treated dosing groups.

RESULTS

CT1812 significantly and dose-dependently displaced Aβ oligomers bound to synaptic receptors in three independent preclinical models of AD, facilitated oligomer clearance into the CSF, increased synaptic number and protein expression in neurons, and improved cognitive performance in transgenic mice. CT1812 significantly increased CSF concentrations of Aβ oligomers in AD patient CSF, reduced concentrations of synaptic proteins and phosphorylated tau fragments, and reversed expression of many AD-related proteins dysregulated in CSF.

DISCUSSION

These preclinical studies demonstrate the novel disease-modifying mechanism of action of CT1812 against AD and Aβ oligomers. The clinical results are consistent with preclinical data and provide evidence of target engagement and impact on fundamental disease-related signaling pathways in AD patients, supporting further development of CT1812.

Quinovic Acid Impedes Cholesterol Dyshomeostasis, Oxidative Stress, and Neurodegeneration in an Amyloid-β-Induced Mouse Model

Alzheimer's disease (AD) is a progressive neurodegenerative disorder typified by several neuropathological features including amyloid-beta (Aβ) plaque and neurofibrillary tangles (NFTs). Cholesterol retention and oxidative stress (OS) are the major contributors of elevated β- and γ-secretase activities, leading to excessive Aβ deposition, signifying the importance of altered cholesterol homeostasis and OS in the progression of Aβ-mediated neurodegeneration and cognitive deficit. However, the effect of Aβ on cholesterol metabolism is lesser-known. In this study, we evaluated the effect of quinovic acid (QA; 50 mg/kg body weight, i.p.) against the intracerebroventricular (i.c.v.) injection of Aβ (1-42)-induced cholesterol dyshomeostasis, oxidative stress, and neurodegeneration in the cortex and hippocampal brain regions of wild-type male C57BL/6J mice. Our results indicated that Aβ (1-42)-treated mice have increased Aβ oligomer formation along with increased β-secretase expression. The enhanced amyloidogenic pathway in Aβ (1-42)-treated mice intensified brain cholesterol accumulation due to increased expressions of p53 and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme. Importantly, we further confirmed the p53-mediated HMGCR axis activation by using pifithrin-α (PFT) in SH-SY5Y cells. Furthermore, the augmented brain cholesterol levels were also associated with increased OS. However, the QA administration to Aβ (1-42)-injected mice significantly ameliorated the Aβ burden, p53 expression, and cholesterol accumulation by deterring the oxidative stress through upregulating the Nrf2/HO-1 pathway. Moreover, the QA downregulated gliosis, neuroinflammatory mediators (p-NF-κB and IL-1β), and the expression of mitochondrial apoptotic markers (Bax, cleaved caspase-3, and cytochrome c). QA treatment also reversed the deregulated synaptic markers (PSD-95 and synaptophysin) and improved spatial learning and memory behaviors in the Aβ-treated mouse brains. These results suggest that Aβ (1-42) induces its acute detrimental effects on cognitive functions probably by increasing brain cholesterol levels through a possible activation of the p53/HMGCR axis. However, QA treatment reduces the cholesterol-induced oxidative stress, neuroinflammation, and neurodegeneration, leading to the restoration of cognitive deficit after Aβ (1-42) i.c.v. injection in mice.

Blood Lipids and Cognitive Performance of Aging Polish Adults: A Case-Control Study Based on the PolSenior Project

Background: The demand for effective strategies for maintaining cognitive capableness and establishing early dementia diagnosis has been tremendous, especially in the context of population aging. However, studies on the elderly population and neurocognitive impairment had provided ambiguous results throughout, while potential blood biomarkers of cognitive decline are yet to be clearly understood.

Objectives: The present study is aimed at assessing the relationship between blood lipids—especially in the context of their usefulness as biomarkers of an early cognitive decline—and cognitive functioning of aging adults.

Materials and Methods: The study sample consisted of 230 participants—(109 women, 121 men) aged 65+ years. Plasma 24(S)-hydroxycholesterol [24(S)-OHC], serum total cholesterol (TC), high-density lipoprotein cholesterol (HDL), and low-density lipoprotein cholesterol (LDL) were assessed. The analyses were conducted in three groups of cognitive performance: cognitively normal, mild cognitive impairment (MCI), and mild dementia, of which the subjects were divided with the Mini-Mental State Examination (MMSE).

Results: No significant differences in 24(S)-OHC plasma concentrations for different levels of cognitive performance were found. Significant differences were found in serum TC (p = 0.026) and LDL (p = 0.007) concentrations for different levels of cognitive performance. Concentrations of both parameters were highest in the MCI group and lowest in mild dementia and cognitive norm, respectively. No significant differences between serum HDL concentrations and cognitive performance were found.

Conclusions: To fully assess the potential of research on blood lipids in regards to a cognitive decline, cross-sectional or epidemiological studies aimed at further exploring blood lipid roles in both the early and advanced MCI and dementia, are needed.

Association of Vascular Risk Factors With β-Amyloid Peptide and Tau Burdens in Cognitively Unimpaired Individuals and Its Interaction With Vascular Medication Use

IMPORTANCE

Vascular risk factors are associated with increased risk of Alzheimer disease (AD), but it is unclear whether there is a direct association of these risk factors with AD pathogenesis.

OBJECTIVES

To assess the associations of vascular risk factors with AD pathogenesis in asymptomatic individuals, and to test whether this association is moderated among individuals who use vascular medications.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study used data from the Presymptomatic Evaluation of Experimental or Novel Treatments for Alzheimer Disease (PREVENT-AD) cohort of cognitively unimpaired individuals aged 55 to 82 years with a parental or multiple-sibling history of sporadic AD, who were recruited via advertisement from the greater Montreal, Quebec, Canada, metropolitan area. Participants were enrolled between September 9, 2011, to May, 3, 2017, and stratified by use vs no use of vascular medications. Data were analyzed July 1, 2018, to April 5, 2019.

MAIN OUTCOMES AND MEASURES

Principal analyses investigated associations of total, high-density lipoprotein, and low-density lipoprotein cholesterol levels, systolic and diastolic blood pressure, pulse pressure, and a combined vascular risk score (measured using the Framingham Coronary Risk Profile) with global β-amyloid peptide (Aβ) and entorhinal tau burden as measured by positron emission tomography (PET). Potential moderating associations of use of vascular medications with these associations were examined. Secondary similar analyses considered cerebrospinal fluid (CSF) Aβ1-42 and phosphorylated tau levels.

RESULTS

Among 215 participants (mean [SD] age, 62.3 [5.0] years; 161 [74.8%] women), 120 participants underwent PET, including 75 participants (62.5%) who were not using vascular medications, and 162 participants underwent CSF assessment, including 113 participants (69.8%) who were not using vascular medications. There was an overlap of 67 participants who underwent PET and CSF assessment. Interaction analyses showed that among participants not using vascular medications, higher Aβ deposition as measured by PET was associated with higher total cholesterol level (β = -0.002 [SE, 0.001]; P = .02), low-density lipoprotein cholesterol level (β = -0.002 [SE, 0.001]; P = .006), systolic blood pressure (β = -0.006 [SE, 0.002]; P = .02), pulse pressure (β = -0.007 [SE, 0.002]; P = .004), and Framingham Coronary Risk Profile score (β = -0.038 [SE, 0.011]; P = .001), but such associations were absent in participants who used vascular medications. Interactions were also found between vascular medication use and high-density lipoprotein cholesterol (β = -3.302 [SE, 1.540]; P = .03), low-density lipoprotein cholesterol (β = 1.546 [SE, 0.754]; P = .04), and Framingham Coronary Risk Profile score (β = 23.102 [SE, 10.993]; P = .04) on Aβ1-42 burden as measured in CSF. Higher Framingham Coronary Risk Profile scores were associated with reduced tau burden among participants using vascular medications but not among participants not using vascular medications (interaction, β = -0.010 [SE, 0.005]; P = .046).

CONCLUSIONS AND RELEVANCE

These findings corroborate previously reported associations of vascular risk factors with Aβ burden but not tau burden. However, these associations were found only among individuals who were not using vascular medications. These results suggest that medication use or other control of vascular risk factors should be considered in Alzheimer disease prevention trials.

Magnetite-OmpA Nanobioconjugates as Cell-Penetrating Vehicles with Endosomal Escape Abilities

Outer membrane protein A (OmpA) has been extensively studied in Gram-negative bacteria due to its relevance in the adhesion of pathogens to host cells and its surfactant capabilities. It consists of a hydrophobic β-barrel domain and a hydrophilic periplasmic domain, that confers OmpA an amphiphilic structure. This study aims to elucidate the capacity of Escherichia coli OmpA to translocate liposomal membranes and serve as a potential cell-penetrating vehicle. We immobilized OmpA on magnetite nanoparticles and investigated the possible functional changes exhibited by OmpA after immobilization. Liposomal intake was addressed using egg lecithin liposomes as a model, where magnetite-OmpA nanobioconjugates were able to translocate the liposomal membrane and caused a disruptive effect when subjected to a magnetic field. Nanobioconjugates showed both low cytotoxicity and hemolytic tendency. Additional interactions within the intracellular space led to altered viability results via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). Confocal microscopy images revealed that immobilized nanoparticles effectively enter the cytoplasm of THP-1 and Vero cells by different routes, and, subsequently, some escape endosomes, lysosomes, and other intracellular compartments with relatively high efficiencies. This was demonstrated by co-localization analyses with LysoTracker green that showed Pearson correlations of about 80 and 28%.

Apolipoprotein E/Amyloid-β Complex Accumulates in Alzheimer Disease Cortical Synapses via Apolipoprotein E Receptors and Is Enhanced by APOE4

Apolipoprotein E (apoE) colocalizes with amyloid-β (Aβ) in Alzheimer disease (AD) plaques and in synapses, and evidence suggests that direct interactions between apoE and Aβ are important for apoE's effects in AD. The present work examines the hypothesis that apoE receptors mediate uptake of apoE/Aβ complex into synaptic terminals. Western blot analysis shows multiple SDS-stable assemblies in synaptosomes from human AD cortex; apoE/Aβ complex was markedly increased in AD compared with aged control samples. Complex formation between apoE and Aβ was confirmed by coimmunoprecipitation experiments. The apoE receptors low-density lipoprotein receptor (LDLR) and LDLR-related protein 1 (LRP1) were quantified in synaptosomes using flow cytometry, revealing up-regulation of LRP1 in early- and late-stage AD. Dual-labeling flow cytometry analysis of LRP1- and LDLR positives indicate most (approximately 65%) of LDLR and LRP1 is associated with postsynaptic density-95 (PSD-95)-positive synaptosomes, indicating that remaining LRP1 and LDLR receptors are exclusively presynaptic. Flow cytometry analysis of Nile red labeling revealed a reduction in cholesterol esters in AD synaptosomes. Dual-labeling experiments showed apoE and Aβ concentration into LDLR and LRP1-positive synaptosomes, along with free and esterified cholesterol. Synaptic Aβ was increased by apoE4 in control and AD samples. These results are consistent with uptake of apoE/Aβ complex and associated lipids into synaptic terminals, with subsequent Aβ clearance in control synapses and accumulation in AD synapses.

Metabolomic insights of macrophage responses to graphene nanoplatelets: Role of scavenger receptor CD36

Graphene nanoplatelets (GNPs) are novel two-dimensional engineered nanomaterials consisting of planar stacks of graphene. Although human exposures are increasing, our knowledge is lacking regarding immune-specific responses to GNPs and mechanisms of interactions. Our current study utilizes a metabolite profiling approach to evaluate macrophage responses to GNPs. Furthermore, we assessed the role of the scavenger receptor CD36 in mediating these GNP-induced responses. GNPs were purchased with dimensions of 2 μm × 2 μm × 12 nm. Macrophages were exposed to GNPs at different concentrations of 0, 25, 50, or 100 μg/ml for 1, 3, or 6 h. Following exposure, no cytotoxicity was observed, while GNPs readily associated with macrophages in a concentration-dependent manner. After the 1h-pretreatment of either a CD36 competitive ligand sulfo-N-succinimidyl oleate (SSO) or a CD36 specific antibody, the cellular association of GNPs by macrophages was significantly reduced. GNP exposure was determined to alter mitochondrial membrane potential while the pretreatment with a CD36 antibody inhibited these changes. In a separate exposure, macrophages were exposed to GNPs at concentrations of 0, 50, or 100 μg/mL for 1 or 3h or 100 μM SSO (a CD36 specific ligand) for 1h and collected for metabolite profiling. Principal component analysis of identified compounds determined differential grouping based on exposure conditions. The number of compounds changed following exposure was determined to be both concentration- and time-dependent. Identified metabolites were determined to relate to several metabolism pathways such as glutathione metabolism, Pantothenate and CoA biosynthesis, Sphingolipid metabolism, Purine metabolism, arachidonic acid metabolism and others. Lastly, a number of metabolites were found in common between cells exposed to the CD36 receptor ligand, SSO, and GNPs suggesting both CD36-dependent and independent responses to GNP exposure. Together our data demonstrates GNP-macrophage interactions, the role of CD36 in the cellular response, and metabolic pathways disrupted due to exposure.

Malaria pigment accelerates MTT - formazan exocytosis in human endothelial cells

Haemozoin is a by-product of haemoglobin digestion by intraerythrocytic malaria parasites, which induces immunologic responses on different tissues, including endothelial cells. In the present paper, the incubation of human microvascular endothelial cells with haemozoin significantly inhibited MTT reduction, a measure of cytotoxicity, without increasing the release of cytoplasmic lactate dehydrogenase. Moreover, haemozoin did not induce apoptosis or cell cycle arrest nor decreased the number of live cells, suggesting that cells viability itself was not affected and that the inhibition of MTT reduction was only apparent and probably due to accelerated MTT-formazan exocytosis. After 30 min of MTT addition, a significant increase in the % of cells exocytosing MTT formazan crystals was observed in haemozoin-treated cells compared with control cells. Such an effect was partially reversed by the addition of genistein, an inhibitor of MTT-formazan exocytosis. The rapid release of CXCL-8, a preformed chemokine contained in Weibel-Palade bodies, confirmed that haemozoin induces a perturbation of the intracellular endothelial trafficking, including the exocytosis of MTT-formazan containing vesicles. The haem moiety of haemozoin is responsible for the observed effect. Moreover, this work underlines that MTT assay should not be used to measure cytotoxicity induced by haemozoin and other methods should be preferred.

Tau Spread, Apolipoprotein E, Inflammation, and More: Rapidly Evolving Basic Science in Alzheimer Disease

To date, Alzheimer disease drug candidates have produced negative results in human trials, and progress in moving new targets out of the laboratory and into trials has been slow. However, based on 3 decades of previous work, there is reason to hope that amyloid-based and other novel therapies will move at a faster pace toward successful clinical trials. This article highlights selected preclinical research topics that are rapidly advancing in the laboratory.

Multinucleated Giant Cancer Cells Produced in Response to Ionizing Radiation Retain Viability and Replicate Their Genome

Loss of wild-type p53 function is widely accepted to be permissive for the development of multinucleated giant cells. However, whether therapy-induced multinucleation is associated with cancer cell death or survival remains controversial. Herein, we demonstrate that exposure of p53-deficient or p21^WAF1 (p21)-deficient solid tumor-derived cell lines to ionizing radiation (between 2 and 8 Gy) results in the development of multinucleated giant cells that remain adherent to the culture dish for long times post-irradiation. Somewhat surprisingly, single-cell observations revealed that virtually all multinucleated giant cells that remain adherent for the duration of the experiments (up to three weeks post-irradiation) retain viability and metabolize 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT), and the majority (>60%) exhibit DNA synthesis. We further report that treatment of multinucleated giant cells with pharmacological activators of apoptosis (e.g., sodium salicylate) triggers their demise. Our observations reinforce the notion that radiation-induced multinucleation may reflect a survival mechanism for p53/p21-deficient cancer cells. With respect to evaluating radiosensitivity, our observations underscore the importance of single-cell experimental approaches (e.g., single-cell MTT) as the creation of viable multinucleated giant cells complicates the interpretation of the experimental data obtained by commonly-used multi-well plate colorimetric assays.

Cholesterol Interferes with the MTT Assay in Human Epithelial-Like (A549) and Endothelial (HLMVE and HCAE) Cells

Metabolically active cells are able to convert the MTT [3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide] dye to blue formazan. This is the basis of the MTT assay, which is among the most widely used screening methods to evaluate cell viability and proliferation. When testing the effects of cholesterol products on the viability of human pulmonary epithelial-like A549 cells using trypan blue staining (cell numbers) and the MTT assay, results were inconsistent. The MTT assay indicated greater than 50% loss of viability with exposure of cells to cholesterol, whereas there was no decrease in viability indicated by trypan blue exclusion and propidium iodide uptake. A similar decrease in MTT reduction was obtained upon cholesterol treatment in human lung microvascular endothelial cells (HLMVECs) and human coronary artery endothelial cells (HCAECs) without loss of viability. This suggested a direct interference of cholesterol with the assay. However, using a cell-free system, there was no decrease in the reduction of MTT by ascorbic acid during incubation with a similar concentration of cholesterol. Light microscopy revealed enhanced exocytosis of formazan granules in presence of cholesterol. Incubation with apolipoprotein A-1 decreased cholesterol-mediated inhibition of MTT assay. These studies indicate decreased MTT reduction as a result of enhanced exocytosis of formazan due to cholesterol. A careful validation of viability assay procedures is therefore suggested in experiments where cholesterol is a constituent, to avoid a potential bias in concluding results of cytotoxicity studies.

The blood brain barrier in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people worldwide. One of the prominent causative factors of AD pathogenesis is cerebral vascular dysfunction, which results in diminished cerebral perfusion. Moreover, due to the loss of the protective function of the blood-brain barrier (BBB), impaired clearance of excess neurotoxic amyloid beta (Aβ) occurs, causing vascular perturbation and diminished cognitive functioning. The relationship between the prevalence of AD and vascular risk factors is complex and not fully understood. In this review we illustrate the vascular risk factors, their effects on BBB function and their contributions to the onset of AD. Additionally, we discuss the underlying factors that may lead to altered neurovascular function and/or cerebral hypoperfusion in AD.

The pleiotropic effects of omega-3 docosahexaenoic acid on the hallmarks of Alzheimer's disease

Among omega-3 polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA, 22:6n-3) is important for adequate brain development and cognition. DHA is highly concentrated in the brain and plays an essential role in brain functioning. DHA, one of the major constituents in fish fats, readily crosses the blood-brain barrier from blood to the brain. Its critical role was further supported by its reduced levels in the brain of Alzheimer's disease (AD) patients. This agrees with a potential role of DHA in memory, learning and cognitive processes. Since there is yet no cure for dementia such as AD, there is growing interest in the role of DHA-supplemented diet in the prevention of AD pathogenesis. Accordingly, animal, epidemiological, preclinical and clinical studies indicated that DHA has neuroprotective effects in a number of neurodegenerative conditions including AD. The beneficial effects of this key omega-3 fatty acid supplementation may depend on the stage of disease progression, other dietary mediators and the apolipoprotein ApoE genotype. Herein, our review investigates, from animal and cell culture studies, the molecular mechanisms involved in the neuroprotective potential of DHA with emphasis on AD.

Pitfalls of the MTT assay: Direct and off-target effects of inhibitors can result in over/underestimation of cell viability

The MTT assay (to a less degree MTS, XTT or WST) is a widely exploited approach for measuring cell viability/drug cytotoxicity. MTT reduction occurs throughout a cell and can be significantly affected by a number of factors, including metabolic and energy perturbations, changes in the activity of oxidoreductases, endo-/exocytosis and intracellular trafficking. Over/underestimation of cell viability by the MTT assay may be due to both adaptive metabolic and mitochondrial reprogramming of cells subjected to drug treatment-mediated stress and inhibitor off-target effects. Previously, imatinib, rottlerin, ursolic acid, verapamil, resveratrol, genistein nanoparticles and some polypeptides were shown to interfere with MTT reduction rate resulting in inconsistent results between the MTT assay and alternative assays. Here, to test the under/overestimation of viability by the MTT assay, we compared results derived from the MTT assay with the trypan blue exclusion assay after treatment of glioblastoma U251, T98G and C6 cells with three widely used inhibitors with the known direct and side effects on energy and metabolic homeostasis - temozolomide (TMZ), a DNA-methylating agent, temsirolimus (TEM), an inhibitor of mTOR kinase, and U0126, an inhibitor of MEK1/2 kinases. Inhibitors were applied shortly as in IC50 evaluating studies or long as in studies focusing on drug resistance acquisition. We showed that over/underestimation of cell viability by the MTT assay and its significance depends on a cell line, a time point of viability measurement and other experimental parameters. Furthermore, we provided a comprehensive survey of factors that should be accounted in the MTT assay. To avoid result misinterpretation, supplementation of the tetrazolium salt-based assays with other non-metabolic assays is recommended.

An in vitro model for synaptic loss in neurodegenerative diseases suggests a neuroprotective role for valproic acid via inhibition of cPLA2 dependent signalling

Many neurodegenerative diseases present the loss of synapses as a common pathological feature. Here we have employed an in vitro model for synaptic loss to investigate the molecular mechanism of a therapeutic treatment, valproic acid (VPA). We show that amyloid-β (Aβ), isolated from patient tissue and thought to be the causative agent of Alzheimer's disease, caused the loss of synaptic proteins including synaptophysin, synapsin-1 and cysteine-string protein from cultured mouse neurons. Aβ-induced synapse damage was reduced by pre-treatment with physiologically relevant concentrations of VPA (10 μM) and a structural variant propylisopropylacetic acid (PIA). These drugs also reduced synaptic damage induced by other neurodegenerative-associated proteins α-synuclein, linked to Lewy body dementia and Parkinson's disease, and the prion-derived peptide PrP82-146. Consistent with these effects, synaptic vesicle recycling was also inhibited by these proteins and protected by VPA and PIA. We show a mechanism for this damage through aberrant activation of cytoplasmic phospholipase A2 (cPLA2) that is reduced by both drugs. Furthermore, Aβ-dependent cPLA2 activation correlates with its accumulation in lipid rafts, and is likely to be caused by elevated cholesterol (stabilising rafts) and decreased cholesterol ester levels, and this mechanism is reduced by VPA and PIA. Such observations suggest that VPA and PIA may provide protection against synaptic damage that occurs during Alzheimer's and Parkinson's and prion diseases.

β2-microglobulin amyloid fibrils are nanoparticles that disrupt lysosomal membrane protein trafficking and inhibit protein degradation by lysosomes

Fragmentation of amyloid fibrils produces fibrils that are reduced in length but have an otherwise unchanged molecular architecture. The resultant nanoscale fibril particles inhibit the cellular reduction of the tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), a substrate commonly used to measure cell viability, to a greater extent than unfragmented fibrils. Here we show that the internalization of β2-microglobulin (β2m) amyloid fibrils is dependent on fibril length, with fragmented fibrils being more efficiently internalized by cells. Correspondingly, inhibiting the internalization of fragmented β2m fibrils rescued cellular MTT reduction. Incubation of cells with fragmented β2m fibrils did not, however, cause cell death. Instead, fragmented β2m fibrils accumulate in lysosomes, alter the trafficking of lysosomal membrane proteins, and inhibit the degradation of a model protein substrate by lysosomes. These findings suggest that nanoscale fibrils formed early during amyloid assembly reactions or by the fragmentation of longer fibrils could play a role in amyloid disease by disrupting protein degradation by lysosomes and trafficking in the endolysosomal pathway.

Cholesterol as a causative factor in Alzheimer's disease: a debatable hypothesis

High serum/plasma cholesterol levels have been suggested as a risk factor for Alzheimer's disease (AD). Some reports, mostly retrospective epidemiological studies, have observed a decreased prevalence of AD in patients taking the cholesterol lowering drugs, statins. The strongest evidence causally linking cholesterol to AD is provided by experimental studies showing that adding/reducing cholesterol alters amyloid precursor protein (APP) and amyloid beta-protein (Ab) levels. However, there are problems with the cholesterol-AD hypothesis. Cholesterol levels in serum/plasma and brain of AD patients do not support cholesterol as a causative factor in AD.Prospective studies on statins and AD have largely failed to show efficacy. Even the experimental data are open to interpretation given that it is well-established that modification of cholesterol levels has effects on multiple proteins, not only amyloid precursor protein and Ab. The purpose of this review, therefore, was to examine the above-mentioned issues, discuss the pros and cons of the cholesterol-AD hypothesis, involvement of other lipids in the mevalonate pathway, and consider that AD may impact cholesterol homeostasis.

Platelet-activating factor antagonists enhance intracellular degradation of amyloid-β42 in neurons via regulation of cholesterol ester hydrolases

INTRODUCTION

The progressive dementia that is characteristic of Alzheimer's disease is associated with the accumulation of amyloid-beta (Aβ) peptides in extracellular plaques and within neurons. Aβ peptides are targeted to cholesterol-rich membrane micro-domains called lipid rafts. Observations that many raft proteins undertake recycling pathways that avoid the lysosomes suggest that the accumulation of Aβ in neurons may be related to Aβ targeting lipid rafts. Here we tested the hypothesis that the degradation of Aβ by neurons could be increased by drugs affecting raft formation.

METHODS

Primary neurons were incubated with soluble Aβ preparations. The amounts of Aβ42 in neurons or specific cellular compartments were measured by enzyme-linked immunosorbent assay. The effects of drugs on the degradation of Aβ42 were studied.

RESULTS

Aβ42 was targeted to detergent-resistant, low-density membranes (lipid rafts), trafficked via a pathway that avoided the lysosomes, and was slowly degraded by neurons (half-life was greater than 5 days). The metabolism of Aβ42 was sensitive to pharmacological manipulation. In neurons treated with the cholesterol synthesis inhibitor squalestatin, less Aβ42 was found within rafts, greater amounts of Aβ42 were found in lysosomes, and the half-life of Aβ42 was reduced to less than 24 hours. Treatment with phospholipase A2 inhibitors or platelet-activating factor (PAF) antagonists had the same effects on Aβ42 metabolism in neurons as squalestatin. PAF receptors were concentrated in the endoplasmic reticulum (ER) along with enzymes that constitute the cholesterol ester cycle. The addition of PAF to ER membranes triggered activation of cholesterol ester hydrolases and the release of cholesterol from stores of cholesterol esters. An inhibitor of cholesterol ester hydrolases (diethylumbelliferyl phosphate) also increased the degradation of Aβ42 in neurons.

CONCLUSIONS

We conclude that the targeting of Aβ42 to rafts in normal cells is a factor that affects its degradation. Critically, pharmacological manipulation of neurons can significantly increase Aβ42 degradation. These results are consistent with the hypothesis that the Aβ-induced production of PAF controls a cholesterol-sensitive pathway that affects the cellular localization and hence the fate of Aβ42 in neurons.

Alzheimer amyloid beta inhibition of Eg5/kinesin 5 reduces neurotrophin and/or transmitter receptor function

The mechanism by which amyloid beta (Aβ) causes neuronal dysfunction and/or death in Alzheimer's disease (AD) is unclear. Previously, we showed that Aβ inhibits several microtubule-dependent kinesin motors essential for mitosis and also present in mature neurons. Here, we show that inhibition of kinesin 5 (Eg5) by Aβ blocks neuronal function by reducing transport of neurotrophin and neurotransmitter receptors to the cell surface. Specifically, cell-surface NGF/NTR(p75) and NMDA receptors decline in cells treated with Aβ or the kinesin 5 inhibitor monastrol, or expressing APP. Aβ and monastrol also inhibit NGF-dependent neurite outgrowth from PC12 cells and glutamate-dependent Ca++ entry into primary neurons. Like Aβ, monastrol inhibits long-term potentiation, a cellular model of NMDA-dependent learning and memory, and kinesin 5 activity is absent from APP/PS transgenic mice brain or neurons treated with Aβ. These data imply that cognitive deficits in AD may derive in part from inhibition of neuronal Eg5 by Aβ, resulting in impaired neuronal function and/or survival through receptor mislocalization. Preventing inhibition of Eg5 or other motors by Aβ may represent a novel approach to AD therapy.

Exocytosis of nanoparticles from cells: role in cellular retention and toxicity

Over the past decade, nanoparticles (NPs) have been increasingly developed in various biomedical applications such as cell tracking, biosensing, contrast imaging, targeted drug delivery, and tissue engineering. Their versatility in design and function has made them an attractive, alternative choice in many biological and biomedical applications. Cellular responses to NPs, their uptake, and adverse biological effects caused by NPs are rapidly-growing research niches. However, NP excretion and its underlying mechanisms and cell signaling pathways are yet elusive. In this review, we present an overview of how NPs are handled intracellularly and how they are excreted from cells following the uptake. We also discuss how exocytosis of nanomaterials impacts both the therapeutic delivery of nanoscale objects and their nanotoxicology.

24S-hydroxycholesterol in plasma: a marker of cholesterol turnover in neurodegenerative diseases

Brain cholesterol is mainly involved in the cell membrane structure, in signal transduction, neurotransmitter release, synaptogenesis and membrane trafficking. Impairment of brain cholesterol metabolism was described in neurodegenerative diseases, such as Multiple Sclerosis, Alzheimer and Huntington Diseases. Since the blood-brain barrier efficiently prevents cholesterol uptake from the circulation into the brain, de novo synthesis is responsible for almost all cholesterol present there. Cholesterol is converted into 24S-hydroxycholesterol (24OHC) by cholesterol 24-hydroxylase (CYP46A1) expressed in neural cells. Plasma concentration of 24OHC depends upon the balance between cerebral production and hepatic elimination and is related to the number of metabolically active neurons in the brain. Factors affecting brain cholesterol turnover and liver elimination of oxysterols, together with the metabolism of plasma lipoproteins, genetic background, nutrition and lifestyle habits were found to significantly affect its plasma levels. Either increased or decreased plasma 24OHC concentrations were described in patients with neurodegenerative diseases. A group of evidence suggests that reduced levels of 24OHC are related to the loss of metabolically active cells and the degree of brain atrophy. Inflammation, dysfunction of BBB, increased cholesterol turnover might counteract this tendency resulting in increased levels or, in some cases, in unsignificant changes. The study of plasma 24OHC is likely to offer an insight about brain cholesterol turnover with a limited diagnostic power.

β-amyloid inhibits protein prenylation and induces cholesterol sequestration by impairing SREBP-2 cleavage

Accumulation of β-amyloid (Aβ) inside brain neurons is an early and crucial event in Alzheimer's disease (AD). Studies in brains of AD patients and mice models of AD suggested that cholesterol homeostasis is altered in neurons that accumulate Aβ. Here we directly investigated the role of intracellular oligomeric Aβ(42) (oAβ(42)) in neuronal cholesterol homeostasis. We report that oAβ(42) induces cholesterol sequestration without increasing cellular cholesterol mass. Several features of AD, such as endosomal abnormalities, brain accumulation of Aβ and neurofibrillary tangles, and influence of apolipoprotein E genotype, are also present in Niemann-Pick type C, a disease characterized by impairment of intracellular cholesterol trafficking. These common features and data presented here suggest that a pathological mechanism involving abnormal cholesterol trafficking could take place in AD. Cholesterol sequestration in Aβ-treated neurons results from impairment of intracellular cholesterol trafficking secondary to inhibition of protein prenylation. oAβ(42) reduces sterol regulatory element-binding protein-2 (SREBP-2) cleavage, causing decrease of protein prenylation. Inhibition of protein prenylation represents a mechanism of oAβ(42)-induced neuronal death. Supply of the isoprenoid geranylgeranyl pyrophosphate to oAβ(42)-treated neurons recovers normal protein prenylation, reduces cholesterol sequestration, and prevents Aβ-induced neurotoxicity. Significant to AD, reduced levels of protein prenylation are present in the cerebral cortex of the TgCRND8 mouse model. In conclusion, we demonstrate a significant inhibitory effect of Aβ on protein prenylation and identify SREBP-2 as a target of oAβ(42), directly linking Aβ to cholesterol homeostasis impairment.

Lipid rafts and Alzheimer's disease: protein-lipid interactions and perturbation of signaling

Lipid rafts are membrane domains, more ordered than the bulk membrane and enriched in cholesterol and sphingolipids. They represent a platform for protein-lipid and protein–protein interactions and for cellular signaling events. In addition to their normal functions, including membrane trafficking, ligand binding (including viruses), axonal development and maintenance of synaptic integrity, rafts have also been implicated in the pathogenesis of several neurodegenerative diseases including Alzheimer’s disease (AD). Lipid rafts promote interaction of the amyloid precursor protein (APP) with the secretase (BACE-1) responsible for generation of the amyloid β peptide, Aβ. Rafts also regulate cholinergic signaling as well as acetylcholinesterase and Aβ interaction. In addition, such major lipid raft components as cholesterol and GM1 ganglioside have been directly implicated in pathogenesis of the disease. Perturbation of lipid raft integrity can also affect various signaling pathways leading to cellular death and AD. In this review, we discuss modulation of APP cleavage by lipid rafts and their components, while also looking at more recent findings on the role of lipid rafts in signaling events.

Reciprocal regulation of cholesterol and beta amyloid at the subcellular level in Alzheimer's disease

Since the discovery that apolipoprotein E, a cholesterol transport protein, is a major risk factor for Alzheimer's disease (AD) development, there has been a remarkable interest in understanding the many facets of the relationship between cholesterol and AD. Several lines of evidence have demonstrated the importance of cholesterol in amyloid beta peptide (Aβ) production and metabolism, as well as the involvement of Aβ in cholesterol homeostasis. The emerging picture is complex and still incomplete. This review discusses findings that indicate that a reciprocal regulation exists between Aβ and cholesterol at the subcellular level. The pathological impact of such regulation is highlighted.

Amyloid β1-42 oligomer inhibits myelin sheet formation in vitro

Accumulating evidence indicates that white matter degeneration contributes to the neural disconnections that underlie Alzheimer's disease pathophysiology. Although this white matter degeneration is partly attributable to axonopathy associated with neuronal degeneration, amyloid β (Aβ) protein-mediated damage to oligodendrocytes could be another mechanism. To test this hypothesis, we studied effects of soluble Aβ in oligomeric form on survival and differentiation of cells of the oligodendroglial lineage using highly purified oligodendroglial cultures from rats at different developmental stages. Aβ oligomer at 10 μM or higher reduced survival of mature oligodendrocytes, whereas oligodendroglial progenitor cells (OPCs) were relatively resistant to the Aβ oligomer-mediated cytotoxicity. Further study revealed that Aβ oligomer even at 1 μM accelerated 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) formazan exocytosis in mature oligodendrocytes, and, more significantly, inhibited myelin sheet formation after induction of in vitro differentiation of OPCs. These results imply a novel pathogenetic mechanism underlying Aβ oligomer-mediated white matter degeneration, which could impair myelin maintenance and remyelination by adult OPCs, resulting in accumulating damage to myelinating axons thereby contributing to neural disconnections.

Compensatory mechanisms to heal neuroplasticity impairment under Alzheiemer's disease neurodegeneration. I: The role of amyloid beta and its' precursor protein

In-depth scholar literature analysis of Alzheimer's disease neurodegenerative features of amyloid beta protein neurochemistry modification and excessive phosphorylation of tau protein (and associated neuronal cytoskeleton rearrangements) are secondary phenomena. At early disease stage these neurobiochemical mechanisms are reversible and serve to heal an impairment of biophysical properties of neuronal membranes, neurotransmission, basic neuronal function and neuroplasticity, while preserving anatomical and functional brain fields. Aβ and tau could well serve to biochemically restore physico-chemical properties of neual membranes due to a role these proteins play in lipid metabolism. Under such scenario therapeutic block of aggregation and plaque formation of Aβ and inhibition of tau phosphorylation, as well as pharmaceutical modification of other secondary neurodegenerative features (such as a cascade of oxidative stress reactions) are unable to provide an effective cure of Alzheimer's disease and related pathologies of the Central and peripheral nervous systems, because they are not arraying primary pathagenetic cause. We review the role of Aβ in compensatory mechanisms of neuroplasticity restoration under normal physiological condition and Alzheimer's disease.

Plasma 24S-hydroxycholesterol levels in elderly subjects with late onset Alzheimer's disease or vascular dementia: a case-control study

BACKGROUND

In central nervous system cholesterol cannot be degraded but is secreted into circulation predominantly in the form of its polar metabolite 24(S)-hydroxycholesterol (24S-OH-Chol). Some studies suggested an association between 24S-OH-Chol metabolism and different neurological diseases including dementia. A possible decrease in 24S-OH-Chol plasma levels has been reported late onset Alzheimer's disease (LOAD) and vascular dementia (VD), but results of previous studies are partially contradictory.

METHODS

By high-speed liquid chromatography/tandem mass spectrometry we evaluated the plasma levels of 24S-OH-Chol in a sample of 160 older individuals: 60 patients with LOAD, 35 patients with VD, 25 subjects affected by cognitive impairment no-dementia (CIND), and 40 (144 for genetics study) cognitively normal Controls. We also investigated the possible association between PPARgamma Pro12Ala polymorphism and dementia or 24S-OH-Chol levels.

RESULTS

Compared with Controls, plasma 24S-OH-Chol levels were higher in LOAD and lower in VD; a slight not-significant increase in CIND was observed (ANOVA p: 0.001). A positive correlation between 24S-OH-Chol/TC ratio and plasma C reactive protein (CRP) levels was found in the whole sample, independent of possible confounders (multiple regression p: 0.04; r2: 0.10). This correlation was strong in LOAD (r: 0.39), still present in CIND (r: 0.20), but was absent in VD patients (r: 0.08). The PPARgamma Pro12Ala polymorphism was not associated with the diagnosis of LOAD, VD, or CIND; no correlation emerged between the Ala allele and 24S-OH-Chol plasma levels.

CONCLUSIONS

Our results suggest that plasma 24S-OH-Chol levels might be increased in the first stages of LOAD, and this phenomenon might be related with systemic inflammation. The finding of lower 24S-OH-Chol concentrations in VD might be related with a more advanced stage of VD compared with LOAD in our sample, and/or to different pathogenetic mechanisms and evolution of these two forms of dementia.

Relationship between cholesterol metabolism, ApoE and brain volumes in Alzheimer’s disease

APOE genotype, aging and midlife hypercholesterolemia are well-established risk factors for late-onset Alzheimer’s disease (AD). ApoE and cholesterol are involved in the pathogenesis of AD since they influence amyloid-β accumulation and Tau pathology. APOE ε4 carriers were found to present lower levels of amyloid-β1–42, higher tau and phosphorylated tau and a higher degree of brain atrophy at any disease stage. Presence of ApoE4 shifts the onset of the disease towards a younger age and makes progression faster. Hypercholesterolemia together with other major cardiovascular risk factors were found to be involved in the pathogenesis of AD, but reduced plasma cholesterol levels were described in demented patients. Significant correlations were found between cholesterol precursors lathosterol, lanosterol and 24S-hydroxycholesterol (a putative marker of brain cholesterol turnover) in plasma and brain atrophy as quantified by MRI. It is likely that neurodegeneration affects both brain and whole-body cholesterol metabolism in AD.

Purified high molecular weight synthetic Aβ(1-42) and biological Aβ oligomers are equipotent in rapidly inducing MTT formazan exocytosis

Synthetic soluble Aβ oligomers are often used as a surrogate for biologic material in a number of model systems. We compared the activity of Aβ oligomers (synthetic and cell culture media derived) on the human SH-SY5Y neuroblastoma and C2C12 mouse myoblast cell lines in a novel, modified MTT assay. Separating oligomers from monomeric peptide by size exclusion chromatography produced effects at peptide concentrations approaching physiologic levels (10-100 nM). Purified oligomers, but not monomers or fibrils, elicited an increase of a detergent-insoluble form of MTT formazan within 2h as opposed to a control toxin (H(2)O(2)). This effect was comparable for biological and synthetic peptide in both cell types. Monomeric Aβ attenuated the effect of soluble oligomers. This study suggests that the activities of biological and synthetic oligomers are indistinguishable during early stages of Aβ oligomer-cell interaction.

Amyloidogenic properties of a D/N mutated 12 amino acid fragment of the C-terminal domain of the Cholesteryl-Ester Transfer Protein (CETP)

The cholesteryl-ester transfer protein (CETP) facilitates the transfer of cholesterol esters and triglycerides between lipoproteins in plasma where the critical site for its function is situated in the C-terminal domain. Our group has previously shown that this domain presents conformational changes in a non-lipid environment when the mutation D(470)N is introduced. Using a series of peptides derived from this C-terminal domain, the present study shows that these changes favor the induction of a secondary β-structure as characterized by spectroscopic analysis and fluorescence techniques. From this type of secondary structure, the formation of peptide aggregates and fibrillar structures with amyloid characteristics induced cytotoxicity in microglial cells in culture. These supramolecular structures promote cell cytotoxicity through the formation of reactive oxygen species (ROS) and change the balance of a series of proteins that control the process of endocytosis, similar to that observed when β-amyloid fibrils are employed. Therefore, a fine balance between the highly dynamic secondary structure of the C-terminal domain of CETP, the net charge, and the physicochemical characteristics of the surrounding microenvironment define the type of secondary structure acquired. Changes in this balance might favor misfolding in this region, which would alter the lipid transfer capacity conducted by CETP, favoring its propensity to substitute its physiological function.

Links between ApoE, brain cholesterol metabolism, tau and amyloid beta-peptide in patients with cognitive impairment

Brain neurons remove the excess of cholesterol via conversion into the more polar 24OHC [(24S)-hydroxycholesterol]. 24OHC acts as a signalling molecule inducing ApoE (apolipoprotein E)-mediated cholesterol efflux from astrocytes, by a direct effect on ApoE transcription, protein synthesis and secretion. In CSF (cerebrospinal fluid) collected form from patients with cognitive impairment (Alzheimer's disease and patients with mild cognitive impairment) the levels of ApoE, tau, p-tau (hyperphosphorylated tau) were significantly increased, together with 24OHC, compared with controls. We also found that the levels of tau and p-tau were significantly correlated with ApoE and 24OHC in the same samples. Such a correlation was not found in control patients. Increased levels of cholesterol in membranes and impairment in brain cholesterol metabolism were found to be involved both in APP (amyloid precursor protein) processing and amyloid beta-peptide deposition and, recently, in tau pathology. The CSF tau levels are considered to be related to the neurodegenerative process in Alzheimer's disease. During neurodegeneration, the cholesterol accumulated in neurons is converted into 24OHC. The release of 24OHC from neurons induces ApoE secretion by astrocytes, and both are related to the intensity of the neurodegenerative process and neuronal injury. ApoE can also be involved in the scavenging of tau from neurons. The direct correlations between ApoE, 24OHC and tau suggest that cholesterol metabolism may be involved in generation of both tau and amyloid beta-peptide and that the ApoE is released by astrocytes in order to counteract this ongoing process.

Minocycline recovers MTT-formazan exocytosis impaired by amyloid beta peptide

Minocycline, a tetracycline antibiotic, has been reported to exert beneficial effects in models of Alzheimer's disease (AD). To characterize the mechanisms underlying the putative minocycline-related neuroprotection, we studied its effect in an in vitro model of AD. Primary hippocampal cultures were treated with β-amyloid peptide (Aβ) and cell viability was assessed by standard MTT-assay. Incubation with 10 μM Aβ for 24 h significantly inhibits cellular MTT-reduction without inducing morphological signs of enhanced cell death or increase in release of lactate dehydrogenase. This indicates that cell viability was not affected. The inhibition of MTT-reduction by Aβ was due to an acceleration of MTT-formazan exocytosis. Intriguingly, the Aβ-triggered increase in MTT-formazan exocytosis was abolished by co-treatment with minocycline. In vehicle-treated cells minocycline had no effect on formazan exocytosis. This hitherto unrecognized property of minocycline has to be noticed in the elucidation of the underlying mechanism of this promising neuroprotectant.

Amyloid-modifying therapies for Alzheimer's disease: therapeutic progress and its implications

Alzheimer's disease (AD) is the most prevalent form of dementia, affecting an estimated 4.8 million people in North America. For the past decade, the amyloid cascade hypothesis has dominated the field of AD research. This theory posits that the deposition of amyloid-beta protein (Abeta) in the brain is the key pathologic event in AD, which induces a series of neuropathological changes that manifest as cognitive decline and eventual dementia. Based on this theory, interventions that reduce Abeta burden in the brain would be expected to alleviate both the neuropathological changes and dementia, which characterize AD. Several diverse pharmacological strategies have been developed to accomplish this. These include inhibiting the formation of Abeta, preventing the aggregation of Abeta into insoluble aggregates, preventing the entry of Abeta into the brain from the periphery and enhancing the clearance of Abeta from the central nervous system. To date, no amyloid-modifying therapy has yet been successful in phase 3 clinical trials; however, several trials are currently underway. This article provides a review of the status of amyloid-modifying therapies and the implications for the amyloid cascade hypothesis.

The effects of cholesterol on learning and memory

Cholesterol is vital to normal brain function including learning and memory but that involvement is as complex as the synthesis, metabolism and excretion of cholesterol itself. Dietary cholesterol influences learning tasks from water maze to fear conditioning even though cholesterol does not cross the blood brain barrier. Excess cholesterol has many consequences including peripheral pathology that can signal brain via cholesterol metabolites, pro-inflammatory mediators and antioxidant processes. Manipulations of cholesterol within the central nervous system through genetic, pharmacological, or metabolic means circumvent the blood brain barrier and affect learning and memory but often in animals already otherwise compromised. The human literature is no less complex. Cholesterol reduction using statins improves memory in some cases but not others. There is also controversy over statin use to alleviate memory problems in Alzheimer's disease. Correlations of cholesterol and cognitive function are mixed and association studies find some genetic polymorphisms are related to cognitive function but others are not. In sum, the field is in flux with a number of seemingly contradictory results and many complexities. Nevertheless, understanding cholesterol effects on learning and memory is too important to ignore.

Cholesterol in Alzheimer's disease and other amyloidogenic disorders

The complex association of cholesterol metabolism and Alzheimer's disease is presented in depth, including the possible benefits to be gained from cholesterol-lowering statin therapy. Then follows a survey of the role of neuronal membrane cholesterol in Abeta pore formation and Abeta fibrillogenesis, together with the link with membrane raft domains and gangliosides. The contribution of structural studies to Abeta fibrillogenesis, using TEM and AFM, is given some emphasis. The role of apolipoprotein E and its isoforms, in particular ApoE4, in cholesterol and Abeta binding is presented, in relation to genetic risk factors for Alzheimer's disease. Increasing evidence suggests that cholesterol oxidation products are of importance in generation of Alzheimer's disease, possibly induced by Abeta-produced hydrogen peroxide. The body of evidence for a link between cholesterol in atherosclerosis and Alzheimer's disease is increasing, along with an associated inflammatory response. The possible role of cholesterol in tau fibrillization, tauopathies and in some other non-Abeta amyloidogenic disorders is surveyed.

Amyloid beta-protein stimulates trafficking of cholesterol and caveolin-1 from the plasma membrane to the Golgi complex in mouse primary astrocytes

The Golgi complex plays a key role in cholesterol trafficking in cells. Our earlier study demonstrated amyloid beta-protein (Abeta) alters cholesterol distribution and abundance in the Golgi complex of astrocytes. We now test the hypothesis that the Abeta-induced increase in Golgi complex cholesterol is due to retrograde movement of the cholesterol carrier protein caveolin-1 from the cell plasma membrane to the Golgi complex in astrocytes. Results with mouse primary astrocytes indicated that Abeta(1-42)-induced increase in cholesterol and caveolin abundance in the Golgi complex was accompanied by a reduction in cholesterol and caveolin levels in the plasma membrane. Transfected rat astrocytes (DITNC1) with siRNA directed at caveolin-1 mRNA inhibited the Abeta(1-42)-induced redistribution of both cholesterol and caveolin from the plasma membrane to the Golgi complex. In astrocytes not treated with Abeta(1-42), suppression of caveolin-1 expression also significantly reduced cholesterol abundance in the Golgi complex, further demonstrating the role for caveolin in retrograde transport of cholesterol from the plasma membrane to the Golgi complex. Perturbation of this process by Abeta(1-42) could have consequences on membrane structure and cellular functions requiring optimal levels of cholesterol.

Alzheimer's disease-type neuronal tau hyperphosphorylation induced by A beta oligomers

Alzheimer's disease (AD) is characterized by presence of extracellular fibrillar A beta in amyloid plaques, intraneuronal neurofibrillary tangles consisting of aggregated hyperphosphorylated tau and elevated brain levels of soluble A beta oligomers (ADDLs). A major question is how these disparate facets of AD pathology are mechanistically related. Here we show that, independent of the presence of fibrils, ADDLs stimulate tau phosphorylation in mature cultures of hippocampal neurons and in neuroblastoma cells at epitopes characteristically hyperphosphorylated in AD. A monoclonal antibody that targets ADDLs blocked their attachment to synaptic binding sites and prevented tau hyperphosphorylation. Tau phosphorylation was blocked by the Src family tyrosine kinase inhibitor, 4-amino-5-(4-chlorophenyl)-7(t-butyl)pyrazol(3,4-D)pyramide (PP1), and by the phosphatidylinositol-3-kinase inhibitor LY294002. Significantly, tau hyperphosphorylation was also induced by a soluble aqueous extract containing A beta oligomers from AD brains, but not by an extract from non-AD brains. A beta oligomers have been increasingly implicated as the main neurotoxins in AD, and the current results provide a unifying mechanism in which oligomer activity is directly linked to tau hyperphosphorylation in AD pathology.

A broadly neuroprotective derivative of curcumin

The plant polyphenolic curcumin alters the response of nerve cells to some forms of toxic stress. The steroid-like compound, cyclohexyl bisphenol A, has broad neuroprotective properties that are very distinct from those of curcumin. To incorporate both families of biological activities into a single molecule, a pyrazole derivative of curcumin, called CNB-001, was synthesized. CNB-001 acquires a new activity and is far superior in neuroprotection assays to either parental molecule, but retains some of the properties of both. It is neuroprotective in cell culture assays for trophic factor withdrawal, oxidative stress, excitotoxicity, and glucose starvation, as well as toxicity from both intracellular and extracellular amyloid. While the creation of CNB-001 was based upon an uncommon approach to drug design, it has the potential of a lead drug candidate for treating multiple conditions involving nerve cell death.

Role of calcium in the pathogenesis of Alzheimer's disease and transgenic models

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the elderly that is characterized by memory loss. Neuropathologically, the AD brain is marked by an increased AP burden, hyperphosphorylated tau aggregates, synaptic loss, and inflammatory responses. Disturbances in calcium homeostasis are also one of the earliest molecular changes that occur in AD patients, alongside alterations in calcium-dependent enzymes in the post-mortem brain. The sum of these studies suggests that calcium dyshomeostasis is an integral part of the pathology, either influencing AP production, mediating its effects or both. Increasing evidence from in vitro studies demonstrates that the AP peptide could modulate a number of ion channels increasing calcium influx, including voltage-gated calcium and potassium channels, the NMDA receptor, the nicotinic receptor, as well as forming its own calcium-conducting pores. In vivo evidence has shown that A3 impairs both LTP and cognition, whereas all of these ion channels cluster at the synapse and underlie synaptic transmission and hence cognition. Here we consider the evidence that AP causes cognitive deficits through altering calcium homeostasis at the synapse, thus impairing synaptic transmission and LTP. Furthermore, this disruption appearr to occur without overt or extensive neuronal loss, as it is observed in transgenic mouse models of AD, but may contribute to the synaptic loss, which is an early event that correlates best with cognitive decline.