Alzheimer's disease: cholesterol, membrane rafts, isoprenoids and statins

Paradoxical effect of Aβ on protein levels of ABCA1 in astrocytes, microglia, and neurons isolated from C57BL/6 mice: an in vitro and in silico study to elucidate the effect of Aβ on ABCA1 in the brain cells

Impaired cholesterol metabolism has been reported in Alzheimer's disease. Since ABCA1 is one of the main players in the brain's cholesterol homeostasis, here we used the in-vitro and in-silico experiments to investigate the effect of Aβ on ABCA1 protein levels in microglia, astrocytes, and neurons in mice. Microglia, astrocytes, and neurons were cultured and exposed to beta amyloid. ABCA1 in cell lysates was determined by Western blotting, and cholesterol efflux was measured in the conditioned media. Molecular docking, molecular dynamics simulations, and MM-GBSA analysis were conducted to gain a better understanding of the effects of Aβ on ABCA1. In response to Aβ, the protein levels of ABCA1 increase significantly in microglia, astrocytes, and neurons; however, its ability to enhance cholesterol efflux is diminished. Aβ inhibited the function of ABCA1 by obstructing the extracellular tunnel that transports lipids outside the cell, as determined by molecular docking. MD simulation analysis validated these findings. Our results demonstrated that Aβ could increase ABCA1 protein levels in various brain cells, regardless of cell type. Molecular docking, molecular dynamics simulation, and MM-GBSA studies indicate that Aβ has a significant effect on the structural conformation of ABCA1, possibly interfering with its function. We believe that the conformational changes of ABCA1 will inhibit its ability to subsequently release cellular cholesterol. Aβ may obstruct the extracellular tunnel of ABCA1, rendering it less accessible to proteases such as the calpain family, which may explain the increase in ABCA1 levels but decrease in its function.Communicated by Ramaswamy H. Sarma.

Entanglement of MAPK pathways with gene expression and its omnipresence in the etiology for cancer and neurodegenerative disorders

Mitogen Activated Protein Kinase (MAPK) is one of the most well characterized cellular signaling pathways that controls fundamental cellular processes including proliferation, differentiation, and apoptosis. These cellular functions are consequences of transcription of regulatory genes that are influenced and regulated by the MAP-Kinase signaling cascade. MAP kinase components such as Receptor Tyrosine Kinases (RTKs) sense external cues or ligands and transmit these signals via multiple protein complexes such as RAS-RAF, MEK, and ERKs and eventually modulate the transcription factors inside the nucleus to induce transcription and other regulatory functions. Aberrant activation, dysregulation of this signaling pathway, and genetic alterations in any of these components results in the developmental disorders, cancer, and neurodegenerative disorders. Over the years, the MAPK pathway has been a prime pharmacological target, to treat complex human disorders that are genetically linked such as cancer, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The current review re-visits the mechanism of MAPK pathways in gene expression regulation. Further, a current update on the progress of the mechanistic understanding of MAPK components is discussed from a disease perspective.

The Interplay Between Cholesterol and Amyloid-β on HT22 Cell Viability, Morphology, and Receptor Tyrosine Kinase Signaling

BACKGROUND

There is a lack of understanding in the molecular and cellular mechanisms of Alzheimer's disease that has hindered progress on therapeutic development. The focus has been on targeting toxic amyloid-β (Aβ) pathology, but these therapeutics have generally failed in clinical trials. Aβ is an aggregation-prone protein that has been shown to disrupt cell membrane structure in molecular biophysics studies and interfere with membrane receptor signaling in cell and animal studies. Whether the lipid membrane or specific receptors are the primary target of attack has not been determined.

OBJECTIVE

This work elucidates some of the interplay between membrane cholesterol and Aβ42 on HT22 neuronal cell viability, morphology, and platelet-derived growth factor (PDGF) signaling pathways.

METHODS

The effects of cholesterol depletion by methyl-β-cyclodextrin followed by treatment with Aβ and/or PDGF-AA were assessed by MTT cell viability assays, western blot, optical and AFM microscopy.

RESULTS

Cell viability studies show that cholesterol depletion was mildly protective against Aβ toxicity. Together cholesterol reduction and Aβ42 treatment compounded the disruption of the PDGFα receptor activation. Phase contrast optical microscopy and live cell atomic force microscopy imaging revealed that cytotoxic levels of Aβ42 caused morphological changes including cell membrane damage, cytoskeletal disruption, and impaired cell adhesion; cell damage was ameliorated by cellular cholesterol depletion.

CONCLUSIONS

Cholesterol depletion impacted the effects of Aβ42 on HT22 cell viability, morphology, and receptor tyrosine kinase signaling.

Amyloid β Dodecamer Disrupts the Neuronal Membrane More Strongly than the Mature Fibril: Understanding the Role of Oligomers in Neurotoxicity

The amyloid cascade hypothesis states that senile plaques, composed of amyloid β (Aβ) fibrils, play a key role in Alzheimer’s disease (AD). However, recent experiments have shown that Aβ oligomers are more toxic to neurons than highly ordered fibrils. The molecular mechanism underlying this observation remains largely unknown. One of the possible scenarios for neurotoxicity is that Aβ peptides create pores in the lipid membrane that allow Ca²⁺ ions to enter cells, resulting in a signal of cell apoptosis. Hence, one might think that oligomers are more toxic due to their higher ability to create ion channels than fibrils. In this work, we study the effect of Aβ42 dodecamer and fibrils on a neuronal membrane, which is similar to that observed in AD patients, using all-atom molecular dynamics simulations. Due to short simulation times, we cannot observe the formation of pores, but useful insight on the early events of this process has been obtained. Namely, we showed that dodecamer distorts the lipid membrane to a greater extent than fibrils, which may indicate that ion channels can be more easily formed in the presence of oligomers. Based on this result, we anticipate that oligomers are more toxic than mature fibrils, as observed experimentally. Moreover, the Aβ–membrane interaction was found to be governed by the repulsive electrostatic interaction between Aβ and the ganglioside GM1 lipid. We calculated the bending and compressibility modulus of the membrane in the absence of Aβ and obtained good agreement with the experiment. We predict that the dodecamer will increase the compressibility modulus but has little effect on the bending modulus. Due to the weak interaction with the membrane, fibrils insignificantly change the membrane elastic properties.

Unravelling the myth surrounding sterol biosynthesis as plausible target for drug design against leishmaniasis

The mortality rate of leishmaniasis is increasing at an alarming rate and is currently second to malaria amongst the other neglected tropical diseases. Unfortunately, many governments and key stakeholders are not investing enough in the development of new therapeutic interventions. The available treatment options targeting different pathways of the parasite have seen inefficiencies, drug resistance, and toxic side effects coupled with longer treatment durations. Numerous studies to understand the biochemistry of leishmaniasis and its pathogenesis have identified druggable targets including ornithine decarboxylase, trypanothione reductase, and pteridine reductase, which are relevant for the survival and growth of the parasites. Another plausible target is the sterol biosynthetic pathway; however, this has not been fully investigated. Sterol biosynthesis is essential for the survival of the Leishmania species because its inhibition could lead to the death of the parasites. This review seeks to evaluate how critical the enzymes involved in sterol biosynthetic pathway are to the survival of the leishmania parasite. The review also highlights both synthetic and natural product compounds with their IC50 values against selected enzymes. Finally, recent advancements in drug design strategies targeting the sterol biosynthesis pathway of Leishmania are discussed.

Vascular Risk Factors and Alzheimer's Disease: Blood-Brain Barrier Disruption, Metabolic Syndromes, and Molecular Links

Alzheimer's disease (AD) is a neurodegenerative disorder, marked by cortical and hippocampal deposition of amyloid-β (Aβ) plaques and neurofibrillary tangles and cognitive impairment. Studies indicate a prominent link between cerebrovascular abnormalities and the onset and progression of AD, where blood-brain barrier (BBB) dysfunction and metabolic disorders play key risk factors. Pericyte degeneration, endothelial cell damage, astrocyte depolarization, diminished tight junction integrity, and basement membrane disarray trigger BBB damage. Subsequently, the altered expression of low-density lipoprotein receptor-related protein 1 and receptor for advanced glycation end products at the microvascular endothelial cells dysregulate Aβ transport across the BBB. White matter lesions and microhemorrhages, dyslipidemia, altered brain insulin signaling, and insulin resistance contribute to tau and Aβ pathogenesis, and oxidative stress, mitochondrial damage, inflammation, and hypoperfusion serve as mechanistic links between pathophysiological features of AD and ischemia. Deregulated calcium homeostasis, voltage gated calcium channel functioning, and protein kinase C signaling are also common mechanisms for both AD pathogenesis and cerebrovascular abnormalities. Additionally, APOE polymorphic alleles that characterize impaired cerebrovascular integrity function as primary genetic determinants of AD. Overall, the current review enlightens key vascular risk factors for AD and underscores pathophysiologic relationship between AD and vascular dysfunction.

Amyloid-Mediated Mechanisms of Membrane Disruption

Protein aggregation and amyloid formation are pathogenic events underlying the development of an increasingly large number of human diseases named “proteinopathies”. Abnormal accumulation in affected tissues of amyloid β (Aβ) peptide, islet amyloid polypeptide (IAPP), and the prion protein, to mention a few, are involved in the occurrence of Alzheimer’s (AD), type 2 diabetes mellitus (T2DM) and prion diseases, respectively. Many reports suggest that the toxic properties of amyloid aggregates are correlated with their ability to damage cell membranes. However, the molecular mechanisms causing toxic amyloid/membrane interactions are still far to be completely elucidated. This review aims at describing the mutual relationships linking abnormal protein conformational transition and self-assembly into amyloid aggregates with membrane damage. A cross-correlated analysis of all these closely intertwined factors is thought to provide valuable insights for a comprehensive molecular description of amyloid diseases and, in turn, the design of effective therapies.

The interplay between lipid and Aβ amyloid homeostasis in Alzheimer's Disease: risk factors and therapeutic opportunities

Alzheimer's Diseases (AD) is characterized by the accumulation of amyloid deposits of Aβ peptide in the brain. Besides genetic background, the presence of other diseases and an unhealthy lifestyle are known risk factors for AD development. Albeit accumulating clinical evidence suggests that an impaired lipid metabolism is related to Aβ deposition, mechanistic insights on the link between amyloid fibril formation/clearance and aberrant lipid interactions are still unavailable. Recently, many studies have described the key role played by membrane bound Aβ assemblies in neurotoxicity. Moreover, it has been suggested that a derangement of the ubiquitin proteasome pathway and autophagy is significantly correlated with toxic Aβ aggregation and dysregulation of lipid levels. Thus, studies focusing on the role played by lipids in Aβ aggregation and proteostasis could represent a promising area of investigation for the design of valuable treatments. In this review we examine current knowledge concerning the effects of lipids in Aβ aggregation and degradation processes, focusing on the therapeutic opportunities that a comprehensive understanding of all biophysical, biochemical, and biological processes involved may disclose.

The efficacy of statins in the treatment of Alzheimer's disease: a meta-analysis of randomized controlled trial

OBJECTIVE

Alzheimer's disease (AD) is a common type of dementia, which has caused heavy global economic and health burden, and the using of statins to treat AD has caused widely debated. The purpose of this meta-analysis is to explore the effect of statins in the treatment of Alzheimer's disease.

METHODS

Studies were retrieved by searching PubMed, Embase, Cochrane library, OvisdSP, Web of Science, Chinese Nation Knowledge Infrastructure (CNKI) and Chinese Biomedical Database (CBM) databases before March 31, 2019. We extracted the Mini-Mental State Examination (MMSE), Alzheimer's Disease Assessment Scale-cognitive (ADAS-Cog), Neuropsychiatric Inventory (NPI), Activities of Daily Living (ADL) scale score, and other information. The pooled Weighted Mean Difference (WMD) and their 95% confidence intervals (95% CI) were calculated with random effect model or fixed random effect model.

RESULTS

A total of nine randomized controlled trials were included that contained 1489 patients; of them, 742 patients in the statins group, 747 patients in the control group. There were nine studies used the MMSE scale, five studies used the ADAS-Cog scale, four studies used the NPI scale, and six studies used the ADL scale. Meta-analysis of the nine studies that reported the MMSE scale scores indicated that there is no significant effect of statins as compared with control group (the pooled WMD = 1.09, 95% CI, - 0.00, 2.18, p = 0.05, I² = 87.9%). Meta-analysis of the five studies that reported the ADAS-Cog scale scores also indicated that there is no significant effect of statins as compared with control group (the pooled WMD = - 0.16, 95% CI, - 2.67, 2.36, p = 0.90, I² = 80.1%). Meta-analysis of the four studies that reported the NPI scale scores indicated that treatment with statins could slow the rise in the NPI scale scores (the pooled WMD = - 1.16, 95% CI, - 1.88, - 0.44, p = 0.002, I² = 45.4%). Meta-analysis of the six studies that reported the ADL scale scores indicated that treatment with statins could improve patients' daily living ability (the pooled WMD = - 4.06, 95% CI, - 6.88, - 1.24, p = 0.005, I² = 86.7%). Results of subgroup analysis indicated that the use of statins in the short term (≤ 12 months) associated with the change of the MMSE scale scores (the pooled WMD = 1.78, 95% CI, 0.53, 3.04, p = 0.005, I² = 79.6%). Sensitivity analysis and publication bias test were both negative, and the results were relatively reliable and stable.

CONCLUSION

Statins used in AD patients had beneficial effects on the scores of MMSE scale in the short term (≤ 12 months), and statins could slow the deterioration of neuropsychiatric status and significantly improve activities of daily living ability in AD patients, but statins did not show an advantage in the change of the ADAS-Cog scale scores.

Emerging roles for high-density lipoproteins in neurodegenerative disorders

Lipoproteins are the complexes of different lipids and proteins, which are devoted to the transport and clearance of lipids or lipid-related molecules in the circulation. Lipoproteins have been found to play a crucial role in brain function and may influence myelination process. Among lipoproteins, high-density lipoproteins (HDLs) and their major protein component, apoA-I, are directly involved in cholesterol efflux in the brain. It has been suggested that inadequate or dysfunctional brain HDLs may contribute to cerebrovascular dysfunctions, neurodegeneration, or neurovascular instability. HDL deficiency could also promote cognitive decline through impacting on atherosclerotic risk. The focus of this review is to discuss knowledge on HDL dysregulation in neurological disorders. A better understanding on how changes in cellular HDL and apolipoprotein homeostasis affect central nervous system function may provide promising novel avenues for the treatment of specific HDL-related neurological disorders.

Alzheimer's Disease as a Membrane Disorder: Spatial Cross-Talk Among Beta-Amyloid Peptides, Nicotinic Acetylcholine Receptors and Lipid Rafts

Biological membranes show lateral and transverse asymmetric lipid distribution. Cholesterol (Chol) localizes in both hemilayers, but in the external one it is mostly condensed in lipid-ordered microdomains (raft domains), together with saturated phosphatidyl lipids and sphingolipids (including sphingomyelin and glycosphingolipids). Membrane asymmetries induce special membrane biophysical properties and behave as signals for several physiological and/or pathological processes. Alzheimer’s disease (AD) is associated with a perturbation in different membrane properties. Amyloid-β (Aβ) plaques and neurofibrillary tangles of tau protein together with neuroinflammation and neurodegeneration are the most characteristic cellular changes observed in this disease. The extracellular presence of Aβ peptides forming senile plaques, together with soluble oligomeric species of Aβ, are considered the major cause of the synaptic dysfunction of AD. The association between Aβ peptide and membrane lipids has been extensively studied. It has been postulated that Chol content and Chol distribution condition Aβ production and posterior accumulation in membranes and, hence, cell dysfunction. Several lines of evidence suggest that Aβ partitions in the cell membrane accumulate mostly in raft domains, the site where the cleavage of the precursor AβPP by β- and γ- secretase is also thought to occur. The main consequence of the pathogenesis of AD is the disruption of the cholinergic pathways in the cerebral cortex and in the basal forebrain. In parallel, the nicotinic acetylcholine receptor has been extensively linked to membrane properties. Since its transmembrane domain exhibits extensive contacts with the surrounding lipids, the acetylcholine receptor function is conditioned by its lipid microenvironment. The nicotinic acetylcholine receptor is present in high-density clusters in the cell membrane where it localizes mainly in lipid-ordered domains. Perturbations of sphingomyelin or cholesterol composition alter acetylcholine receptor location. Therefore, Aβ processing, Aβ partitioning, and acetylcholine receptor location and function can be manipulated by changes in membrane lipid biophysics. Understanding these mechanisms should provide insights into new therapeutic strategies for prevention and/or treatment of AD. Here, we discuss the implications of lipid-protein interactions at the cell membrane level in AD.

Cholesterol in phospholipid bilayers: positions and orientations inside membranes with different unsaturation degrees

Cholesterol is an essential component of all animal cell membranes and plays an important role in maintaining the membrane structure and physical-chemical properties necessary for correct cell functioning. The presence of cholesterol is believed to be responsible for domain formation (lipid rafts) due to different interactions of cholesterol with saturated and unsaturated lipids. In order to get detailed atomistic insight into the behaviour of cholesterol in bilayers composed of lipids with varying degrees of unsaturation, we have carried out a series of molecular dynamics simulations of saturated and polyunsaturated lipid bilayers with different contents of cholesterol, as well as well-tempered metadynamics simulations with a single cholesterol molecule in these bilayers. From these simulations we have determined distributions of cholesterol across the bilayer, its orientational properties, free energy profiles, and specific interactions of molecular groups able to form hydrogen bonds. Both molecular dynamics and metadynamics simulations showed that the most unsaturated bilayer with 22:6 fatty acid chains shows behaviour which is most different from other lipids. In this bilayer, cholesterol is relatively often found in a "flipped" configuration with the hydroxyl group oriented towards the membrane middle plane. This bilayer has also the highest (least negative) binding free energy among liquid phase bilayers, and the lowest reorientation barrier. Furthermore, cholesterol molecules in this bilayer are often found to form head-to-tail contacts which may lead to specific clustering behaviour. Overall, our simulations support ideas that there can be a subtle interconnection between the contents of highly unsaturated fatty acids and cholesterol, deficiency or excess of each of them is related to many human afflictions and diseases.

Connecting the brain cholesterol and renin-angiotensin systems: potential role of statins and RAS-modifying medications in dementia

Millions of people worldwide receive agents targeting the renin-angiotensin system (RAS) to treat hypertension or statins to lower cholesterol. The RAS and cholesterol metabolic pathways in the brain are autonomous from their systemic counterparts and are interrelated through the cholesterol metabolite 27-hydroxycholesterol (27-OHC). These systems contribute to memory and dementia pathogenesis through interference in the amyloid-beta cascade, vascular mechanisms, glucose metabolism, apoptosis, neuroinflammation and oxidative stress. Previous studies examining the relationship between these treatments and cognition and dementia risk have produced inconsistent results. Defining the blood-brain barrier penetration of these medications has been challenging, and the mechanisms of action on cognition are not clearly established. Potential biases are apparent in epidemiological and clinical studies, such as reverse epidemiology, indication bias, problems defining medication exposure, uncertain and changing doses, and inappropriate grouping of outcomes and medications. This review summarizes current knowledge of the brain cholesterol and RAS metabolism and the mechanisms by which these pathways affect neurodegeneration. The putative mechanisms of action of statins and medications inhibiting the RAS will be examined, together with prior clinical and animal studies on their effects on cognition. We review prior epidemiological studies, analysing their strengths and biases, and identify areas for future research. Understanding the pathophysiology of the brain cholesterol system and RAS and their links to neurodegeneration has enormous potential. In future, well-designed epidemiological studies could identify potential treatments for Alzheimer's disease (AD) amongst medications that are already in use for other indications.

Membrane Aging as the Real Culprit of Alzheimer's Disease: Modification of a Hypothesis

Our previous studies proposed that Alzheimer's disease (AD) is a metabolic disorder and hypothesized that abnormal brain glucose metabolism inducing multiple pathophysiological cascades contributes to AD pathogenesis. Aging is one of the great significant risk factors for AD. Membrane aging is first prone to affect the function and structure of the brain by impairing glucose metabolism. We presume that risk factors of AD, including genetic factors (e.g., the apolipoprotein E ε4 allele and genetic mutations) and non-genetic factors (such as fat, diabetes, and cardiac failure) accelerate biomembrane aging and lead to the onset and development of the disease. In this review, we further modify our previous hypothesis to demonstrate "membrane aging" as an initial pathogenic factor that results in functional and structural alterations of membranes and, consequently, glucose hypometabolism and multiple pathophysiological cascades.

Inhibition of Inflammation Mediated Through the Tumor Necrosis Factor α Biochemical Pathway Can Lead to Favorable Outcomes in Alzheimer Disease

Tumor necrosis factor α (TNF-α) inhibitors have long been used as disease-modifying agents in immune disorders. Recently, research has shown a role of chronic neuroinflammation in the pathophysiology of neurodegenerative diseases such as Alzheimer disease, and interest has been generated in the use of anti-TNF agents and TNF-modulating agents for prevention and treatment. This article extensively reviewed literature on animal studies testing these agents. The results showed a role for direct and indirect TNF-α inhibition through agents such as thalidomide, 3,6-dithiothalidomide, etanercept, infliximab, exendin-4, sodium hydrosulfide, minocycline, imipramine, and atorvastatin. Studies were performed on mice, rats, and monkeys, with induction of neurodegenerative physiology either through the use of chemical agents or through the use of transgenic animals. Most of these agents showed an improvement in cognitive function as tested with the Morris water maze, and immunohistochemical and histopathological staining studies consistently showed better outcomes with these agents. Brains of treated animals showed significant reduction in pro-inflammatory TNF-α and reduced the burden of neurofibrillary tangles, amyloid precursor protein, and β-amyloid plaques. Also, recruitment of microglial cells in the central nervous system was significantly reduced through these drugs. These studies provide a clearer mechanistic understanding of the role of TNF-α modulation in Alzheimer disease. All studies in this review explored the use of these drugs as prophylactic agents to prevent Alzheimer disease through immune modulation of the TNF inflammatory pathway, and their success highlights the need for further research of these drugs as therapeutic agents.

ABCA1 Polymorphism, a Genetic Risk Factor of Harm Avoidance

Abstract. Even though cholesterol homeostasis and self-harm behaviors have shown to be associated, gene polymorphisms of the cholesterol system have not been studied yet in the context of self-harm related personality traits. Here we present an association study between six ABCA1 polymorphisms and temperament scales measured by Cloninger’s Temperament and Character Inventory on 253 young adults. An association between ABCA1 rs4149264 and harm avoidance has been observed. This association remained significant after Bonferroni correction. Haplotype analysis confirmed an independent association between rs4149264 and harm avoidance. ABCA1, a cholesterol homeostasis gene, is a candidate gene for harm related personality traits.

Pharmacophore Mapping of Thienopyrimidine-Based Monophosphonate (ThP-MP) Inhibitors of the Human Farnesyl Pyrophosphate Synthase

The human farnesyl pyrophosphate synthase (hFPPS), a key regulatory enzyme in the mevalonate pathway, catalyzes the biosynthesis of the C-15 isoprenoid farnesyl pyrophosphate (FPP). FPP plays a crucial role in the post-translational prenylation of small GTPases that perform a plethora of cellular functions. Although hFPPS is a well-established therapeutic target for lytic bone diseases, the currently available bisphosphonate drugs exhibit poor cellular uptake and distribution into nonskeletal tissues. Recent drug discovery efforts have focused primarily on allosteric inhibition of hFPPS and the discovery of non-bisphosphonate drugs for potentially treating nonskeletal diseases. Hit-to-lead optimization of a new series of thienopyrimidine-based monosphosphonates (ThP-MPs) led to the identification of analogs with nanomolar potency in inhibiting hFPPS. Their interactions with the allosteric pocket of the enzyme were characterized by crystallography, and the results provide further insight into the pharmacophore requirements for allosteric inhibition.

Evidence for benefit of statins to modify cognitive decline and risk in Alzheimer's disease

Background

Despite substantial research and development investment in Alzheimer’s disease (AD), effective therapeutics remain elusive. Significant emerging evidence has linked cholesterol, β-amyloid and AD, and several studies have shown a reduced risk for AD and dementia in populations treated with statins. However, while some clinical trials evaluating statins in general AD populations have been conducted, these resulted in no significant therapeutic benefit. By focusing on subgroups of the AD population, it may be possible to detect endotypes responsive to statin therapy.

Methods

Here we investigate the possible protective and therapeutic effect of statins in AD through the analysis of datasets of integrated clinical trials, and prospective observational studies.

Results

Re-analysis of AD patient-level data from failed clinical trials suggested by trend that use of simvastatin may slow the progression of cognitive decline, and to a greater extent in ApoE4 homozygotes. Evaluation of continual long-term use of various statins, in participants from multiple studies at baseline, revealed better cognitive performance in statin users. These findings were supported in an additional, observational cohort where the incidence of AD was significantly lower in statin users, and ApoE4/ApoE4-genotyped AD patients treated with statins showed better cognitive function over the course of 10-year follow-up.

Conclusions

These results indicate that the use of statins may benefit all AD patients with potentially greater therapeutic efficacy in those homozygous for ApoE4.

Predicting dementia in primary care patients with a cardiovascular health metric: a prospective population-based study

Background

Improving cardiovascular health possibly decreases the risk of dementia. Primary care practices offer a suitable setting for monitoring and controlling cardiovascular risk factors in the older population. The purpose of the study is to examine the association of a cardiovascular health metric including six behaviors and blood parameters with the risk of dementia in primary care patients.

Methods

Participants (N = 3547) were insurants aged ≥55 of the largest German statutory health insurance company, who were enrolled in a six-year prospective population-based study. Smoking, physical activity, body mass index, blood pressure, total cholesterol, and fasting glucose were assessed by general practitioners at routine examinations. Using recommended cut-offs for each factor, the patients’ cardiovascular health was classified as ideal, moderate, or poor. Behaviors and blood parameters sub-scores, as well as a total score, were calculated. Dementia diagnoses were retrieved from health insurance claims data. Results are presented as hazard ratios (HRs) and 95 % confidence intervals (95 % CIs).

Results

Over the course of the study 296 new cases of dementia occurred. Adjusted for age, sex, and education, current smoking (HR = 1.77, 95 % CI 1.09–2.85), moderate (1.38, 1.05–1.81) or poor (1.81, 1.32–2.47) levels of physical activity, and poor fasting glucose levels (1.43, 1.02–2.02) were associated with an increased risk of dementia. Body mass index, blood pressure, and cholesterol were not associated with dementia. Separate summary scores for behaviors and blood values, as well as a total score showed no association with dementia. Sensitivity analyses with differently defined endpoints led to similar results.

Conclusions

Due to complex relationships of body-mass index and blood pressure with dementia individual components cancelled each other out and rendered the sum-scores meaningless for the prediction of dementia.

Oxidized cholesterol as the driving force behind the development of Alzheimer's disease

Alzheimer’s disease (AD), the most common neurodegenerative disorder associated with dementia, is typified by the pathological accumulation of amyloid Aβ peptides and neurofibrillary tangles (NFT) within the brain. Considerable evidence indicates that many events contribute to AD progression, including oxidative stress, inflammation, and altered cholesterol metabolism. The brain’s high lipid content makes it particularly vulnerable to oxidative species, with the consequent enhancement of lipid peroxidation and cholesterol oxidation, and the subsequent formation of end products, mainly 4-hydroxynonenal and oxysterols, respectively from the two processes. The chronic inflammatory events observed in the AD brain include activation of microglia and astrocytes, together with enhancement of inflammatory molecule and free radical release. Along with glial cells, neurons themselves have been found to contribute to neuroinflammation in the AD brain, by serving as sources of inflammatory mediators. Oxidative stress is intimately associated with neuroinflammation, and a vicious circle has been found to connect oxidative stress and inflammation in AD. Alongside oxidative stress and inflammation, altered cholesterol metabolism and hypercholesterolemia also significantly contribute to neuronal damage and to progression of AD. Increasing evidence is now consolidating the hypothesis that oxidized cholesterol is the driving force behind the development of AD, and that oxysterols are the link connecting the disease to altered cholesterol metabolism in the brain and hypercholesterolemia; this is because of the ability of oxysterols, unlike cholesterol, to cross the blood brain barrier (BBB). The key role of oxysterols in AD pathogenesis has been strongly supported by research pointing to their involvement in modulating neuroinflammation, Aβ accumulation, and cell death. This review highlights the key role played by cholesterol and oxysterols in the brain in AD pathogenesis.

Target risk factors for dementia prevention: a systematic review and Delphi consensus study on the evidence from observational studies

OBJECTIVE

Dementia has a multifactorial etiology, but the importance of individual health and lifestyle related risk factors is often uncertain or based on few studies. The goal of this paper is to identify the major modifiable risk factors for dementia as a first step in developing an effective preventive strategy and promoting healthy late life cognitive functioning.

METHODS

A mixed-method approach combined findings from a systematic literature review and a Delphi consensus study. The literature search was conducted in PubMed and updated an earlier review by the United States National Institutes of Health from 2010. We reviewed the available evidence from observational epidemiological studies. The online Delphi study asked eight international experts to rank and weigh each risk factor for its importance for dementia prevention.

RESULTS

Out of 3127 abstracts, 291 were included in the review. There was good agreement between modifiable risk factors identified in the literature review and risk factors named spontaneously by experts. After triangulation of both methods and re-weighting by experts, strongest support was found for depression, (midlife) hypertension, physical inactivity, diabetes, (midlife) obesity, hyperlipidemia, and smoking, while more research is needed for coronary heart disease, renal dysfunction, diet, and cognitive activity.

CONCLUSIONS

Findings provide good support for several somatic and lifestyle factors and will be used to inform the design of a new multicenter trial into dementia prevention.

Serum cholesterol and variant in cholesterol-related gene CETP predict white matter microstructure

Several common genetic variants influence cholesterol levels, which play a key role in overall health. Myelin synthesis and maintenance are highly sensitive to cholesterol concentrations, and abnormal cholesterol levels increase the risk for various brain diseases, including Alzheimer's disease. We report significant associations between higher serum cholesterol (CHOL) and high-density lipoprotein levels and higher fractional anisotropy in 403 young adults (23.8 ± 2.4 years) scanned with diffusion imaging and anatomic magnetic resonance imaging at 4 Tesla. By fitting a multi-locus genetic model within white matter areas associated with CHOL, we found that a set of 18 cholesterol-related, single-nucleotide polymorphisms implicated in Alzheimer's disease risk predicted fractional anisotropy. We focused on the single-nucleotide polymorphism with the largest individual effects, CETP (rs5882), and found that increased G-allele dosage was associated with higher fractional anisotropy and lower radial and mean diffusivities in voxel-wise analyses of the whole brain. A follow-up analysis detected white matter associations with rs5882 in the opposite direction in 78 older individuals (74.3 ± 7.3 years). Cholesterol levels may influence white matter integrity, and cholesterol-related genes may exert age-dependent effects on the brain.

Cellular membrane fluidity in amyloid precursor protein processing

The senile plaque is a pathologic hallmark of Alzheimer's disease (AD). Amyloid-β peptide (Aβ), the main constituent of senile plaques, is neurotoxic especially in its oligomeric form. Aβ is derived from the sequential cleavage of amyloid precursor protein (APP) by β- and γ-secretases in the amyloidogenic pathway. Alternatively, APP can be cleaved by α-secretases within the Aβ domain to produce neurotrophic and neuroprotective α-secretase-cleaved soluble APP (sAPPα) in the nonamyloidogenic pathway. Since APP and α-, β-, and γ-secretases are membrane proteins, APP processing should be highly dependent on the membrane composition and the biophysical properties of cellular membrane. In this review, we discuss the role of the biophysical properties of cellular membrane in APP processing, especially the effects of phospholipases A(2) (PLA(2)s), fatty acids, cholesterol, and Aβ on membrane fluidity in relation to their effects on APP processing.

From cholesterogenesis to steroidogenesis: role of riboflavin and flavoenzymes in the biosynthesis of vitamin D

Flavin-dependent monooxygenases and oxidoreductases are located at critical branch points in the biosynthesis and metabolism of cholesterol and vitamin D. These flavoproteins function as obligatory intermediates that accept 2 electrons from NAD(P)H with subsequent 1-electron transfers to a variety of cytochrome P450 (CYP) heme proteins within the mitochondria matrix (type I) and the (microsomal) endoplasmic reticulum (type II). The mode of electron transfer in these systems differs slightly in the number and form of the flavin prosthetic moiety. In the type I mitochondrial system, FAD-adrenodoxin reductase interfaces with adrenodoxin before electron transfer to CYP heme proteins. In the microsomal type II system, a diflavin (FAD/FMN)-dependent cytochrome P450 oxidoreductase [NAD(P)H-cytochrome P450 reductase (CPR)] donates electrons to a multitude of heme oxygenases. Both flavoenzyme complexes exhibit a commonality of function with all CYP enzymes and are crucial for maintaining a balance of cholesterol and vitamin D metabolites. Deficits in riboflavin availability, imbalances in the intracellular ratio of FAD to FMN, and mutations that affect flavin binding domains and/or interactions with client proteins result in marked structural alterations within the skeletal and central nervous systems similar to those of disorders (inborn errors) in the biosynthetic pathways that lead to cholesterol, steroid hormones, and vitamin D and their metabolites. Studies of riboflavin deficiency during embryonic development demonstrate congenital malformations similar to those associated with genetic alterations of the flavoenzymes in these pathways. Overall, a deeper understanding of the role of riboflavin in these pathways may prove essential to targeted therapeutic designs aimed at cholesterol and vitamin D metabolism.

Neurotrophic and metabotrophic potential of nerve growth factor and brain-derived neurotrophic factor: Linking cardiometabolic and neuropsychiatric diseases

One of biggest recent achievements of neurobiology is the study on neurotrophic factors. The neurotrophins are exciting examples of these factors. They belong to a family of proteins consisting of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), NT-4/5, NT-6, and NT-7. Today, NGF and BDNF are well recognized to mediate a dizzying number of trophobiological effects, ranging from neurotrophic through immunotrophic and epitheliotrophic to metabotrophic effects. These are implicated in the pathogenesis of various diseases. In the same vein, recent studies in adipobiology reveal that this tissue is the body’s largest endocrine and paracrine organ producing multiple signaling proteins collectively termed adipokines, with NGF and BDNF being also produced from adipose tissue. Altogether, neurobiology and adipobiology contribute to the improvement of our knowledge on diseases beyond obesity such as cardiometabolic (atherosclerosis, type 2 diabetes, and metabolic syndrome) and neuropsychiatric (e.g., Alzheimer’s disease and depression) diseases. The present review updates evidence for (1) neurotrophic and metabotrophic potentials of NGF and BDNF linking the pathogenesis of these diseases, and (2) NGF- and BDNF-mediated effects in ampakines, NMDA receptor antagonists, antidepressants, selective deacetylase inhibitors, statins, peroxisome proliferator-activated receptor gamma agonists, and purinergic P2X₃ receptor up-regulation. This may help to construct a novel paradigm in the field of translational pharmacology of neuro-metabotrophins, particularly NGF and BDNF.

The effects of age and gender on the relationship between HMGCR promoter-911 SNP (rs33761740) and serum lipids in patients with coronary heart disease

BACKGROUND

Hydroxymethylglutaryl-Coenzyme A Reductase (HMGCR) catalyzes the rate-limiting step of cholesterol biosynthesis. This enzyme is the target of the widely available cholesterol lowering statins. In this population-based case-control study, the frequencies of -911 C>A polymorphism (rs3761740) of the HMGCR gene in patients with coronary heart disease (CHD) and healthy subjects were investigated and the correlations between the different genotypes and hypercholesterolemia with cardiovascular risk factors were analyzed.

METHODS

The HMGCR genotypes were determined in 365 patients with CHD and 365 controls by PCR-RFLP assay. Anthropometric measurements were measured in all participants.

RESULTS

There was no significant difference in the genotype frequencies of the HMGCR polymorphism between the male subjects of both patient and control groups, however, the HMGCR-CC genotype was found to be more frequent in female patients with CHD than female controls (p=0.002). The HMGCR-CC genotype showed higher total-cholesterol (TC) and LDL-cholesterol (LDL-C) levels than the CA+AA genotypes in male CHD patients (p=0.018). Due to this significant sex interaction, a multivariate analysis was conducted on the patient group. In the multivariate logistic regression analysis, the HMGCR-CC genotype was significantly associated with age<55 (OR=2.837, p=0.001) and TC ≥ 5.18 mmol/L (OR=1.970, p=0.027) in male subjects. However, this association was not observed in female patients (p>0.05). This analysis confirmed that the HMGCR-CC genotype was associated with elevated TC levels in male CHD patients with age<55 years.

CONCLUSION

These results suggest that age and sex modify the contribution of the HMGCR-911 polymorphism to fasting serum TC, LDL-C levels and risk of CHD.

Intracerebral propagation of Alzheimer's disease: strengthening evidence of a herpes simplex virus etiology

BACKGROUND

A faulty human protein, abnormally phosphorylated tau, was recently publicized to spread "like a virus" from neuron to neuron in Alzheimer's patients' brains. For several decades, we have been amassing arguments showing that herpes simplex virus type 1 (HSV-1), not p-tau, propagates this interneuronal, transsynaptic pathologic cascade.

METHODS

We reiterate convincing data from our own (and other) laboratories, reviewing the first anatomic foothold neurofibrillary tangles gain in brainstem and/or entorhinal cortex; the chronic immunosurveillance cellularity of the trigeminal ganglia wherein HSV-1 awakens from latency to reactivate; the inabilities of p-tau protein's physical properties to promote it to jump synapses; the amino acid homology between human p-tau and VP22, a key target for phosphorylation by HSV serine/threonine-protein kinase UL13; and the exosomic secretion of HSV-1-infected cells' L-particles, attesting to the cell-to-cell passage of microRNAs of herpesviruses.

RESULTS

The now-maturing construct that reactivated HSV-1 best accounts for the intracerebral propagation of AD changes in the human brain should at last seem highly attractive. This hypothesis might even explain statins' apparent mechanism in some studies for lowering AD incidence.

CONCLUSION

Provided that funding agencies will quickly ignite a new realm of investigation, the rejuvenated enthusiasm for testing this optimistic construct holds incalculable potential for rapid, efficacious clinical application, through already available and relatively safe antiviral therapeutics.

Atorvastatin attenuates the production of IL-1β, IL-6, and TNF-α in the hippocampus of an amyloid β1-42-induced rat model of Alzheimer's disease

Background and aim

Amyloid-beta (Aβ) peptide is reported to initiate flexible inflammation in the hippocampus of the human brain in Alzheimer’s disease (AD). The present study aimed to investigate the possible effects of atorvastatin on the production of inflammation cytokines in the hippocampus and the potential impacts on behavioral ability, in an AD model.

Methods

We firstly established AD rat models using intracerebroventricular injection of Aβ1-42. A Morris water maze was also performed to determine the spatial learning and memory ability in the AD models. Intracellular staining of interleukin (IL)-1β, IL-6, and tumor necrosis factor alpha was determined using immunohistochemical staining at 6 hours and day 7 after the injection of Aβ.

Results

The escape latency of the atorvastatin-treated AD group (5 mg/kg/d) was significantly shorter than that of AD group on day 3 (41 ± 1.05 seconds versus 47 ± 1.05 seconds, P < 0.01) and day 4 (34 ± 1.25 seconds versus 43 ± 1.01 seconds, P < 0.01) after the beginning of the training. Furthermore, the atorvastatin-treated AD group displayed a significant higher mean number of annulus crossings than did the AD group (2.9 ± 0.5 versus 2.4 ± 0.9, P < 0.05). Fewer injured nerve cells and proliferated glial cells were also demonstrated in the atorvastatin-treated AD group than in the AD group. Of great importance, we demonstrated that IL-1β, IL-6, and tumor necrosis factor alpha were significantly decreased in the atorvastatin-treated AD group than that in the AD group.

Conclusion

Atorvastatin might attenuate the damage of nerve cells and improve learning and memory ability by inhibiting inflammatory response in the progression of AD.

Alzheimer's disease, cholesterol, and statins: the junctions of important metabolic pathways

Recent years have seen a significant increase in published data supporting the positive effects of statins on neurodegenerative diseases, in particular on Alzheimer's disease. Statins show neuroprotective activity by a combination of different cellular and systemic mechanisms that are based on the inhibition of the biosynthesis of cholesterol and isoprenoid by-products. The promising results obtained in vivo and in epidemiological studies are generally not in accordance with those of placebo-controlled randomized clinical trials. Nevertheless, these results make statins valuable assets for disease prevention rather than therapeutic agents for use when disease symptoms are already displayed. Thus, the modulation of midlife cholesterol and/or statin administration prior to the appearance of dementia or cognitive impairment may have a better long-term outcome.

The link between altered cholesterol metabolism and Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is characterized by the progressive loss of neurons and synapses, and by extracellular deposits of amyloid-β (Aβ) as senile plaques, Aβ deposits in the cerebral blood vessels, and intracellular inclusions of hyperphosphorylated tau in the form of neurofibrillary tangles. Several mechanisms contribute to AD development and progression, and increasing epidemiological and molecular evidence suggests a key role of cholesterol in its initiation and progression. Altered cholesterol metabolism and hypercholesterolemia appear to play fundamental roles in amyloid plaque formation and tau hyperphosphorylation. Over the last decade, growing evidence supports the idea that cholesterol oxidation products, known as oxysterols, may be the missing link between altered brain cholesterol metabolism and AD pathogenesis, as their involvement in neurotoxicity, mainly by interacting with Aβ peptides, is reported.

AlzPathway: a comprehensive map of signaling pathways of Alzheimer's disease

Background

Alzheimer’s disease (AD) is the most common cause of dementia among the elderly. To clarify pathogenesis of AD, thousands of reports have been accumulating. However, knowledge of signaling pathways in the field of AD has not been compiled as a database before.

Description

Here, we have constructed a publicly available pathway map called “AlzPathway” that comprehensively catalogs signaling pathways in the field of AD. We have collected and manually curated over 100 review articles related to AD, and have built an AD pathway map using CellDesigner. AlzPathway is currently composed of 1347 molecules and 1070 reactions in neuron, brain blood barrier, presynaptic, postsynaptic, astrocyte, and microglial cells and their cellular localizations. AlzPathway is available as both the SBML (Systems Biology Markup Language) map for CellDesigner and the high resolution image map. AlzPathway is also available as a web service (online map) based on Payao system, a community-based, collaborative web service platform for pathway model curation, enabling continuous updates by AD researchers.

Conclusions

AlzPathway is the first comprehensive map of intra, inter and extra cellular AD signaling pathways which can enable mechanistic deciphering of AD pathogenesis. The AlzPathway map is accessible at http://alzpathway.org/.

Cholesterol level influences opioid signaling in cell models and analgesia in mice and humans

Cholesterol regulates the signaling of µ-opioid receptor in cell models, but it has not been demonstrated in mice or humans. Whether cholesterol regulates the signaling by mechanisms other than supporting the entirety of lipid raft microdomains is still unknown. By modulating cholesterol-enriched lipid raft microdomains and/or total cellular cholesterol contents in human embryonic kidney cells stably expressing µ-opioid receptor, we concluded that cholesterol stabilized opioid signaling both by supporting the lipid raft's entirety and by facilitating G protein coupling. Similar phenomena were observed in the primary rat hippocampal neurons. In addition, reducing the brain cholesterol level with simvastatin impaired the analgesic effect of opioids in mice, whereas the opioid analgesic effect was enhanced in mice fed a high-cholesterol diet. Furthermore, when the records of patients were analyzed, an inverse correlation between cholesterol levels and fentanyl doses used for anesthesia was identified, which suggested the mechanisms above could also be applicable to humans. Our results identified the interaction between opioids and cholesterol, which should be considered in clinics as a probable route for drug-drug interaction. Our studies also suggested that a low cholesterol level could lead to clinical issues, such as the observed impairment in opioid functions.

SorLA in glia: shared subcellular distribution patterns with caveolin-1

SorLA is an established sorting and trafficking protein in neurons with demonstrated relevance to Alzheimer's disease (AD). It shares these roles with the caveolins, markers of membrane rafts microdomains. To further our knowledge on sorLA's expression and traffic, we studied sorLA expression in various cultured glia and its relation to caveolin-1 (cav-1), a caveolar microdomain marker. RT-PCR and immunoblots demonstrated sorLA expression in rat C6 glioma, primary cultures of rat astrocytes (PCRA), and human astrocytoma 1321N1 cells. PCRA were determined to express the highest levels of sorLA's message. Induction of differentiation of C6 cells into an astrocyte-like phenotype led to a significant decrease in sorLA's mRNA and protein expression. A set of complementary experimental approaches establish that sorLA and cav-1 directly or indirectly interact in glia: (1) co-fractionation in light-density membrane raft fractions of rat C6 glioma, PCRA, and human 1321N1 astrocytoma cells; (2) a subcellular co-localization distribution pattern in vesicular perinuclear compartments seen via confocal imaging in C6 and PCRA; (3) additional confocal analysis in C6 cells suggesting that the perinuclear compartments correspond to their co-localization in early endosomes and the trans-Golgi; and; (4) co-immunoprecipitation data strongly supporting their direct or indirect physical interaction. These findings further establish that sorLA is expressed in glia and that it shares its subcellular distribution pattern with cav-1. A direct or indirect cav-1/sorLA interaction could modify the trafficking and sorting functions of sorLA in glia and its proposed neuroprotective role in AD.

Increases in β-amyloid protein in the hippocampus caused by diabetic metabolic disorder are blocked by minocycline through inhibition of NF-κB pathway activation

Activation of the NF-κB pathway plays an important role in the pathophysiology of Alzheimer's disease (AD), and blocking NF-κB pathway activation has been shown to attenuate cognitive impairment. Diabetic metabolic disorder contributes to β-amyloid protein (Aβ) generation. The goal of this study was to determine the effect of minocycline on Aβ generation and the NF-κB pathway in the hippocampus of diabetic rats and to elucidate the neuroprotective mechanisms of minocycline for the treatment of diabetic metabolic disorder. The diabetic rat model was established using a high-fat diet and an intraperitoneal injection of streptozocin (STZ). Behavioral tests showed that the capacity of learning and memory was significantly lower in diabetic rats. The levels of NF-κB, COX-2, iNOS, IL-1β and TNF-α after the STZ injection were significantly increased in the hippocampus. Significant increases in Aβ, BACE1, NF-κB, COX-2, iNOS, IL-1β and TNF-α were found in diabetic rats. The levels of Aβ, NF-κB, COX-2, iNOS, IL-1β and TNF-α were significantly decreased after minocycline administration; however, minocycline had no effect on BACE1 expression. In sum, diabetes contributes to the activation of the NF-κB pathway and upregulates BACE1 and Aβ. Minocycline downregulates Aβ in the hippocampus by inhibiting NF-κB pathway activation.

Analysis of amyloid precursor protein function in Drosophila melanogaster

Amyloid precursor proteins (APPs) are evolutionary conserved from nematodes to man (Jacobsen and Iverfeldt in Cell Mol Life Sci 66:2299-2318, 2009) suggesting an important physiological function of these proteins. Human APP is a key factor in the pathogenesis of Alzheimer's Disease because its proteolytic processing results in the production of the neurotoxic Aβ-peptide, which accumulates in the amyloid plaques characteristic for this disease (Selkoe in Physiol Rev 81(2):741-766, 2001). However, the processing also leads to the production of several other fragments and the role of these products, as well as the function of the full-length protein is so far not well understood. The functional analysis of APP in vertebrates has been hampered by the fact that two close relatives, APLP1 and APLP2, exist and that knock-out mice for APP only show subtle defects. In contrast, invertebrates like Caenorhabditis elegans and Drosophila express only one APP-like protein but whereas a null mutation in the C. elegans APL-1 protein is lethal, flies lacking APPL (Amyloid Precursor Protein-like) are viable but show synaptic defects and behavioral abnormalities. Together with the analyses of flies that express APP proteins ectoptically or xenotopically, these studies show that APP proteins are involved in neuronal differentiation, neuritic outgrowth, and synapse formation. In addition, they play a role in long-term memory formation and maintaining brain integrity in adult flies.

Caloric intake, dietary lifestyles, macronutrient composition, and alzheimer' disease dementia

Alzheimer's disease is a devastating neurodegenerative condition currently affecting over 5 million elderly individuals in the United States. There is much evidence suggesting that certain dietary lifestyles can help to prevent and possibly treat Alzheimer's disease. In this paper, we discuss how certain cardiovascular and diabetic conditions can induce an increased susceptibility for Alzheimer's disease and the mechanisms through which this occurs. We further discuss how the consumption of certain foods or food components can help to reduce one's risk for Alzheimer's disease and may possibly be developed as a therapeutic agent.

Cholesterol and LDL relate to neuritic plaques and to APOE4 presence but not to neurofibrillary tangles

Elevated serum total cholesterol (TC) has been considered a risk factor for Alzheimer's disease (AD), but conflicting results have confused understanding of the relationships of serum lipids to the presence of AD in the elderly.

METHODS

To clarify these issues, we evaluated correlations of admission TC, low-density (LDL) and high-density (HDL)cholesterol directly with the densities of Alzheimer hallmarks--neuritic plaques (NP) and neurofibrillary tangles (NFT)--in nursing home residents (n=281).

RESULTS

Significant positive associations of TC and LDL with NP densities were found in both the neocortex (TC: r=0.151, p=0.013 and LDL: r=0.190, p=0.005) and the hippocampal/entorhinal (allocortical)region (TC: r=0.182, p=0.002 and LDL: r=0.203, p=0.003). Associations of HDL with NP were less strong but also significant.In contrast, after adjustment for confounders, no correlations of NFT with any lipid were significant.When subjects with any non-AD neuropathology (largely vascular) were excluded, the TC-plaque and LDL-plaque associations for the remaining "Pure AD" subgroup were consistently stronger than for the full sample. The TC- and LDL-plaque correlations were also stronger for the subgroup of 87 subjects with an APOE ε4 allele.

CONCLUSIONS

The findings indicate that serum TC and LDL levels clearly relate to densities of NP, but not to densities of NFT. The stronger associations found in the subgroup that excluded all subjects with non-AD neuropathology suggest that cerebrovascular involvement does not explain these lipid-plaque relationships. Since the associations of TC/LDL with NP were particularly stronger in ε4 carriers, varying prevalence of this allele may explain some discrepancies among prior studies.

Systemic and central immunity in Alzheimer's disease: therapeutic implications

Clinical pharmaceutical trials aimed at modulating the immune system in Alzheimer's Disease have largely focused on either dampening down central proinflammatory innate immunity or have manipulated adaptive immunity to facilitate the removal of centrally deposited beta amyloid. To date, these trials have had mixed clinical therapeutic effects. However, a number of clinical studies have demonstrated disturbances of both systemic and central innate immunity in Alzheimer's Disease and attention has been drawn to the close communication pathways between central and systemic immunity. This paper highlights the need to take into account the potential systemic effects of drugs aimed at modulating central immunity and the possibility of developing novel therapeutic approaches based on the manipulation of systemic immunity and its communication with the central nervous system.

Impacts of membrane biophysics in Alzheimer's disease: from amyloid precursor protein processing to aβ Peptide-induced membrane changes

An increasing amount of evidence supports the notion that cytotoxic effects of amyloid-β peptide (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD), are strongly associated with its ability to interact with membranes of neurons and other cerebral cells. Aβ is derived from amyloidogenic cleavage of amyloid precursor protein (AβPP) by β- and γ-secretase. In the nonamyloidogenic pathway, AβPP is cleaved by α-secretases. These two pathways compete with each other, and enhancing the non-amyloidogenic pathway has been suggested as a potential pharmacological approach for the treatment of AD. Since AβPP, α-, β-, and γ-secretases are membrane-associated proteins, AβPP processing and Aβ production can be affected by the membrane composition and properties. There is evidence that membrane composition and properties, in turn, play a critical role in Aβ cytotoxicity associated with its conformational changes and aggregation into oligomers and fibrils. Understanding the mechanisms leading to changes in a membrane's biophysical properties and how they affect AβPP processing and Aβ toxicity should prove to provide new therapeutic strategies for prevention and treatment of AD.

Association of higher levels of high-density lipoprotein cholesterol in elderly individuals and lower risk of late-onset Alzheimer disease

OBJECTIVE

To reexamine the association of lipid levels with Alzheimer disease (AD) using Cox proportional hazards models.

DESIGN

Prospective cohort study.

SETTING

Northern Manhattan, New York.

PARTICIPANTS

One thousand one hundred thirty elderly individuals free of cognitive impairment at baseline.

MAIN OUTCOME MEASURE

High-density lipoprotein cholesterol (HDL-C) levels.

RESULTS

Higher levels of HDL-C (>55 mg/dL) were associated with a decreased risk of both probable and possible AD and probable AD compared with lower HDL-C levels (hazard ratio, 0.4; 95% confidence interval, 0.2-0.9; P = .03 and hazard ratio, 0.4; 95% confidence interval, 0.2-0.9; P = .03). In addition, higher levels of total and non-HDL-C were associated with a decreased risk of AD in analyses adjusting for age, sex, education, ethnic group, and APOE e4 genotype.

CONCLUSION

High HDL-C levels in elderly individuals may be associated with a decreased risk of AD.

Systems biology approaches and tools for analysis of interactomes and multi-target drugs

Systems biology is essentially a proteomic and epigenetic exercise because the relatively condensed information of genomes unfolds on the level of proteins. The flexibility of cellular architectures is not only mediated by a dazzling number of proteinaceous species but moreover by the kinetics of their molecular changes: The time scales of posttranslational modifications range from milliseconds to years. The genetic framework of an organism only provides the blue print of protein embodiments which are constantly shaped by external input. Indeed, posttranslational modifications of proteins represent the scope and velocity of these inputs and fulfil the requirements of integration of external spatiotemporal signal transduction inside an organism. The optimization of biochemical networks for this type of information processing and storage results in chemically extremely fine tuned molecular entities. The huge dynamic range of concentrations, the chemical diversity and the necessity of synchronisation of complex protein expression patterns pose the major challenge of systemic analysis of biological models. One further message is that many of the key reactions in living systems are essentially based on interactions of moderate affinities and moderate selectivities. This principle is responsible for the enormous flexibility and redundancy of cellular circuitries. In complex disorders such as cancer or neurodegenerative diseases, which initially appear to be rooted in relatively subtle dysfunctions of multimodal physiologic pathways, drug discovery programs based on the concept of high affinity/high specificity compounds ("one-target, one-disease"), which has been dominating the pharmaceutical industry for a long time, increasingly turn out to be unsuccessful. Despite improvements in rational drug design and high throughput screening methods, the number of novel, single-target drugs fell much behind expectations during the past decade, and the treatment of "complex diseases" remains a most pressing medical need. Currently, a change of paradigm can be observed with regard to a new interest in agents that modulate multiple targets simultaneously, essentially "dirty drugs." Targeting cellular function as a system rather than on the level of the single target, significantly increases the size of the drugable proteome and is expected to introduce novel classes of multi-target drugs with fewer adverse effects and toxicity. Multiple target approaches have recently been used to design medications against atherosclerosis, cancer, depression, psychosis and neurodegenerative diseases. A focussed approach towards "systemic" drugs will certainly require the development of novel computational and mathematical concepts for appropriate modelling of complex data. But the key is the extraction of relevant molecular information from biological systems by implementing rigid statistical procedures to differential proteomic analytics.

Effects of fatty acid unsaturation numbers on membrane fluidity and α-secretase-dependent amyloid precursor protein processing

Fatty acids may integrate into cell membranes to change physical properties of cell membranes, and subsequently alter cell functions in an unsaturation number-dependent manner. To address the roles of fatty acid unsaturation numbers in cellular pathways of Alzheimer's disease (AD), we systematically investigated the effects of fatty acids on cell membrane fluidity and α-secretase-cleaved soluble amyloid precursor protein (sAPP(α)) secretion in relation to unsaturation numbers using stearic acid (SA, 18:0), oleic acid (OA, 18:1), linoleic acid (LA, 18:2), α-linolenic acid (ALA, 18:3), arachidonic acid (AA, 20:4), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6). Treatments of differentiated human neuroblastoma (SH-SY5Y cells) with AA, EPA and DHA for 24h increased sAPP(α) secretion and membrane fluidity, whereas those treatments with SA, OA, LA and ALA did not. Treatments with AA and DHA did not alter the total expressions of amyloid precursor protein (APP) and α-secretases in SH-SY5Y cells. These results suggested that not all unsaturated fatty acids but only those with 4 or more double bonds, such as AA, EPA and DHA, are able to increase membrane fluidity and lead to increase in sAPP(α) secretion. This study provides insights into dietary strategies for the prevention of AD.

Altered levels and distribution of amyloid precursor protein and its processing enzymes in Niemann-Pick type C1-deficient mouse brains

Niemann-Pick type C (NPC) disease is an autosomal recessive neurodegenerative disorder characterized by intracellular accumulation of cholesterol and glycosphingolipids in many tissues including the brain. The disease is caused by mutations of either NPC1 or NPC2 gene and is accompanied by a severe loss of neurons in the cerebellum, but not in the hippocampus. NPC pathology exhibits some similarities with Alzheimer's disease, including increased levels of amyloid beta (Abeta)-related peptides in vulnerable brain regions, but very little is known about the expression of amyloid precursor protein (APP) or APP secretases in NPC disease. In this article, we evaluated age-related alterations in the level/distribution of APP and its processing enzymes, beta- and gamma-secretases, in the hippocampus and cerebellum of Npc1(-/-) mice, a well-established model of NPC pathology. Our results show that levels and expression of APP and beta-secretase are elevated in the cerebellum prior to changes in the hippocampus, whereas gamma-secretase components are enhanced in both brain regions at the same time in Npc1(-/-) mice. Interestingly, a subset of reactive astrocytes in Npc1(-/-) mouse brains expresses high levels of APP as well as beta- and gamma-secretase components. Additionally, the activity of beta-secretase is enhanced in both the hippocampus and cerebellum of Npc1(-/-) mice at all ages, while the level of C-terminal APP fragments is increased in the cerebellum of 10-week-old Npc1(-/-) mice. These results, taken together, suggest that increased level and processing of APP may be associated with the development of pathology and/or degenerative events observed in Npc1(-/-) mouse brains.

Capillary cerebral amyloid angiopathy identifies a distinct APOE epsilon4-associated subtype of sporadic Alzheimer's disease

The deposition of amyloid beta-protein (Abeta) in the vessel wall, i.e., cerebral amyloid angiopathy (CAA), is associated with Alzheimer's disease (AD). Two types of CAA can be differentiated by the presence or absence of capillary Abeta-deposits. In addition, as in Alzheimer's disease, risk for capillary CAA is associated with the apolipoprotein E (APOE) epsilon4-allele. Because these morphological and genetic differences between the two types of AD-related CAA exist, the question arises as to whether there exist further differences between AD cases with and without capillary CAA and, if so, whether capillary CAA can be employed to distinguish and define specific subtypes of AD. To address this question, we studied AD and control cases both with and without capillary CAA to identify the following: (1) distinguishing neuropathological features; (2) alterations in perivascular protein expression; and (3) genotype-specific associations. More widespread Abeta-plaque pathology was observed in AD cases with capillary CAA than in those without. Expression of perivascular excitatory amino acid transporter 2 (EAAT-2/GLT-1) was reduced in cortical astrocytes of AD cases with capillary CAA in contrast to those lacking capillary Abeta-deposition and controls. Genetically, AD cases with capillary CAA were strongly associated with the APOE epsilon4 allele compared to those lacking capillary CAA and to controls. To further validate the existence of distinct types of AD we analyzed polymorphisms in additional apoE- and cholesterol-related candidate genes. Our results revealed an association between AD cases without capillary CAA (i.e., AD cases with CAA but lacking capillary CAA and AD cases without CAA) and the T-allele of the alpha(2)macroglobulin receptor/low-density lipoprotein receptor-related protein-1 (LRP-1) C766T polymorphism as opposed to AD cases with capillary CAA and non-AD controls. Taken together, these results indicate that AD cases with capillary CAA differ significantly from other AD cases both genetically and morphologically, thereby pointing to a specific capillary CAA-related and APOE epsilon4-associated subtype of AD.