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Cholesterol levels have been repeatedly linked to Alzheimer's Disease (AD), suggesting that high levels could be detrimental, but this effect is likely attributed to Low-Density Lipoprotein (LDL) cholesterol. On the other hand, High-Density Lipoproteins (HDL) cholesterol levels have been associated with reduced brain amyloidosis and improved cognitive function. However, recent findings have suggested that HDL-functionality, which depends upon the HDL-cargo proteins associated with HDL, rather than HDL levels, appears to be the key factor, suggesting a quality over quantity status. In this report, we have assessed the HDL-cargo (Cholesterol, ApoA-I, ApoA-II, ApoC-I, ApoC-III, ApoD, ApoE, ApoH, ApoJ, CRP, and SAA) in stable healthy control (HC), healthy controls who will convert to MCI/AD (HC-Conv) and AD patients (AD). Compared to HC we observed an increased cholesterol/ApoA-I ratio in AD and HC-Conv, as well as an increased ApoD/ApoA-I ratio and a decreased ApoA-II/ApoA-I ratio in AD. Higher cholesterol/ApoA-I ratio was also associated with lower cortical grey matter volume and higher ventricular volume, while higher ApoA-II/ApoA-I and ApoJ/ApoA-I ratios were associated with greater cortical grey matter volume (and for ApoA-II also with greater hippocampal volume) and smaller ventricular volume. Additionally, in a clinical status-independent manner, the ApoE/ApoA-I ratio was significantly lower in APOE ε4 carriers and lowest in APOE ε4 homozygous. Together, these data indicate that in AD patients the composition of HDL is altered, which may affect HDL functionality, and such changes are associated with altered regional brain volumetric data.

High-density lipoproteins (HDL) are a heterogeneous class of molecules whose main function is to remove excess cholesterol through a mechanism called reverse transport, in which cholesterol is transported from peripheral organs and from arterial foam cells to the liver, where it is subsequently eliminated with bile. While its ability to eliminate excess cholesterol has always been viewed as its main feature, its beneficial effects go beyond this single effect. Many of the proteins that are associated with HDL are responsible for anti-oxidant and anti-inflammatory properties. These proteins that are associated with HDL during its generation and remodelling, are referred to as 'protein cargo', which has been extensively analysed by mass spectrometry analysis in healthy and diseased individuals. In this review, we discuss the pathway that leads to HDL formation and its subsequent remodelling and catabolism with regards to the possible involvement of HDL 'protein cargo' in Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that currently has no cure. Identifying biochemical changes associated with neurodegeneration prior to symptom onset, will provide insight into the biological mechanisms associated with neurodegenerative processes, that may also aid in identifying potential drug targets. The current study therefore investigated associations between plasma neurofilament light chain (NF-L), a marker of neurodegeneration, with plasma metabolites that are products of various cellular processes. Plasma NF-L, measured by ultrasensitive Single molecule array (Simoa) technology (Quanterix) and plasma metabolites, measured by mass-spectrometry (AbsoluteIDQ® p400HR kit, BIOCRATES), were assessed in the Kerr Anglican Retirement Village Initiative in Ageing Health (KARVIAH) cohort comprising 100 cognitively normal older adults. Metabolites belonging to biogenic amine (creatinine, symmetric dimethylarginine, asymmetric dimethylarginine; ADMA, kynurenine, trans-4-hydroxyproline), amino acid (citrulline, proline, arginine, asparagine, phenylalanine, threonine) and acylcarnitine classes were observed to have positive correlations with plasma NF-L, suggesting a link between neurodegeneration and biological pathways associated with neurotransmitter regulation, nitric oxide homoeostasis, inflammation and mitochondrial function. Additionally, after stratifying participants based on low/high brain amyloid-β load (Aβ ±) assessed by positron emission tomography, while creatinine, SDMA and citrulline correlated with NF-L in both Aβ- and Aβ+ groups, ADMA, proline, arginine, asparagine, phenylalanine and acylcarnitine species correlated with NF-L only in the Aβ+ group after adjusting for confounding variables, suggesting that the association of these metabolites with neurodegeneration may be relevant to AD-related neuropathology. Metabolites identified to be associated with plasma NF-L may have the potential to serve as prognostic markers for neurodegenerative diseases, however, further studies are required to validate the current findings in an independent cohort, both cross-sectionally and longitudinally.

Mitochondrial dysfunction including deficits of mitophagy is seen in aging and neurodegenerative disorders including Alzheimer’s disease (AD). Apart from traditionally targeting amyloid beta (Aβ), the main culprit in AD brains, other approaches include investigating impaired mitochondrial pathways for potential therapeutic benefits against AD. Thus, a future therapy for AD may focus on novel candidates that enhance optimal mitochondrial integrity and turnover. Bioactive food components, known as nutraceuticals, may serve as such agents to combat AD. Urolithin A is an intestinal microbe-derived metabolite of a class of polyphenols, ellagitannins (ETs). Urolithin A is known to exert many health benefits. Its antioxidant, anti-inflammatory, anti-atherogenic, anti-Aβ, and pro-mitophagy properties are increasingly recognized. However, the underlying mechanisms of urolithin A in inducing mitophagy is poorly understood. This review discusses the mitophagy deficits in AD and examines potential molecular mechanisms of its activation. Moreover, the current knowledge of urolithin A is discussed, focusing on its neuroprotective properties and its potential to induce mitophagy. Specifically, this review proposes potential mechanisms by which urolithin A may activate and promote mitophagy.

Previous studies have indicated that physical activity may be beneficial in reducing the risk for Alzheimer's disease (AD), although the underlying mechanisms are not fully understood. The goal of this study was to evaluate the relationship between habitual physical activity levels and brain amyloid deposition and AD-related blood biomarkers (i.e., measured using a novel high-performance mass spectrometry-based assay), in apolipoprotein E (APOE) ε4 carriers and noncarriers. We evaluated 143 cognitively normal older adults, all of whom had brain amyloid deposition assessed using positron emission tomography and had their physical activity levels measured using the International Physical Activity Questionnaire (IPAQ). We observed an inverse correlation between brain amyloidosis and plasma beta-amyloid (Aβ)1−42 but found no association between brain amyloid and plasma Aβ1−40 and amyloid precursor protein (APP)669−711. Additionally, higher levels of physical activity were associated with lower plasma Aβ1−40, Aβ1−42, and APP669−711 levels in APOE ε4 noncarriers. The ratios of Aβ1−40/Aβ1−42 and APP669−711/Aβ1−42, which have been associated with higher brain amyloidosis in previous studies, differed between APOE ε4 carriers and non-carriers. Taken together, these data indicate a complex relationship between physical activity and brain amyloid deposition and potential blood-based AD biomarkers in cognitively normal older adults. In addition, the role of APOE ε4 is still unclear, and more studies are necessary to bring further clarification.

Introduction This study involved a parallel comparison of the diagnostic and longitudinal monitoring potential of plasma glial fibrillary acidic protein (GFAP), total tau (t-tau), phosphorylated tau (p-tau181 and p-tau231), and neurofilament light (NFL) in preclinical Alzheimer's disease (AD). Methods Plasma proteins were measured using Simoa assays in cognitively unimpaired older adults (CU), with either absence (Aβ−) or presence (Aβ+) of brain amyloidosis. Results Plasma GFAP, t-tau, p-tau181, and p-tau231 concentrations were higher in Aβ+ CU compared with Aβ− CU cross-sectionally. GFAP had the highest effect size and area under the curve (AUC) in differentiating between Aβ+ and Aβ− CU; however, no statistically significant differences were observed between the AUCs of GFAP, p-tau181, and p-tau231, but all were significantly higher than the AUC of NFL, and the AUC of GFAP was higher than the AUC of t-tau. The combination of a base model (BM), comprising the AD risk factors, age, sex, and apolipoprotein E gene (APOE) e4 status with GFAP was observed to have a higher AUC (>90%) compared with the combination of BM with any of the other proteins investigated in the current study. Longitudinal analyses showed increased GFAP and p-tau181 in Aβ+ CU and increased NFL in Aβ− CU, over a 12-month duration. GFAP, p-tau181, p-tau231, and NFL showed significant correlations with cognition, whereas no significant correlations were observed with hippocampal volume. Discussion These findings highlight the diagnostic and longitudinal monitoring potential of GFAP and p-tau for preclinical AD.

Introduction Neuronal p3-Alcβ peptides are generated from the precursor protein Alcadein β (Alcβ) through cleavage by α- and γ-secretases of the amyloid β (Aβ) protein precursor (APP). To reveal whether p3-Alcβ is involved in Alzheimer's disease (AD) contributes for the development of novel therapy and/or drug targets. Methods We developed new sandwich enzyme-linked immunosorbent assay (sELISA) systems to quantitate levels of p3-Alcβ in the cerebrospinal fluid (CSF). Results In monkeys, CSF p3-Alcβ decreases with age, and the aging is also accompanied by decreased brain expression of Alcβ. In humans, CSF p3-Alcβ levels decrease to a greater extent in those with AD than in age-matched controls. Subjects carrying presenilin gene mutations show a significantly lower CSF p3-Alcβ level. A cell study with an inverse modulator of γ-secretase remarkably reduces the generation of p3-Alcβ37 while increasing the production of Aβ42. Discussion Aging decreases the generation of p3-Alcβ, and further significant decrease of p3-Alcβ caused by aberrant γ-secretase activity may accelerate pathogenesis in AD.

Mitochondria perform many essential cellular functions including energy production, calcium homeostasis, transduction of metabolic and stress signals, and mediating cell survival and death. Maintaining viable populations of mitochondria is therefore critical for normal cell function. The selective disposal of damaged mitochondria, by a pathway known as mitophagy, plays a key role in preserving mitochondrial integrity and quality. Mitophagy reduces the formation of reactive oxygen species and is considered as a protective cellular process. Mitochondrial dysfunction and deficits of mitophagy have important roles in aging and especially in neurodegenerative disorders such as Alzheimer’s disease (AD). Targeting mitophagy pathways has been suggested to have potential therapeutic effects against AD. In this review, we aim to briefly discuss the emerging concepts on mitophagy, molecular regulation of the mitophagy process, current mitophagy detection methods, and mitophagy dysfunction in AD. Finally, we will also briefly examine the stimulation of mitophagy as an approach for attenuating neurodegeneration in AD.

Background: The link between cholesterol and Alzheimer’s disease (AD) has received much attention, as evidence suggests high levels of cholesterol might be an AD risk factor. The carriage of cholesterol and lipids through the body is mediated via lipoproteins, some of which, particularly apolipoprotein E (ApoE), are intimately linked with AD. In humans, high density lipoprotein (HDL) is regarded as a “good” lipid complex due to its ability to enable clearance of excess cholesterol via ‘cholesterol reverse transport’, although its activities in the pathogenesis of AD are poorly understood. There are several subclasses of HDL; these range from the newly formed small HDL, to much larger HDL. Objective: We examined the major subclasses of HDL in healthy controls, mild cognitively impaired, and AD patients who were not taking statins to determine whether there were HDL profile differences between the groups, and whether HDL subclass levels correlated with plasma amyloid-β (Aβ) levels or brain Aβ deposition. Methods: Samples from AIBL cohort were used in this study. HDL subclass levels were assessed by Lipoprint while Aβ1–42 levels were assessed by ELISA. Brain Aβ deposition was assessed by PET scan. Statistical analysis was performed using parametric and non-parametric tests. Results: We found that small HDL subclass is reduced in AD patients and it correlates with cognitive performance while plasma Aβ concentrations do not correlate with lipid profile or HDL subfraction levels. Conclusion: Our data indicate that AD patients exhibit altered plasma HDL profile and that HDL subclasses correlate with cognitive performances.

Worldwide there are over 46 million people living with dementia, and this number is expected to double every 20 years reaching about 131 million by 2050. The cost to the community and government health systems, as well as the stress on families and carers is incalculable. Over three decades of research into this disease have been undertaken by several research groups in Australia, including work by our original research group in Western Australia which was involved in the discovery and sequencing of the amyloid-β peptide (also known as Aβ or A4 peptide) extracted from cerebral amyloid plaques. This review discusses the journey from the discovery of the Aβ peptide in Alzheimer’s disease (AD) brain to the establishment of pre-clinical AD using PET amyloid tracers, a method now serving as the gold standard for developing peripheral diagnostic approaches in the blood and the eye. The latter developments for early diagnosis have been largely achieved through the establishment of the Australian Imaging Biomarker and Lifestyle research group that has followed 1,100 Australians for 11 years. AIBL has also been instrumental in providing insight into the role of the major genetic risk factor apolipoprotein E ɛ4, as well as better understanding the role of lifestyle factors particularly diet, physical activity and sleep to cognitive decline and the accumulation of cerebral Aβ.

Introduction This study assessed the utility of cerebrospinal fluid (CSF) neurofilament light (NfL) in Alzheimer's disease (AD) diagnosis, its association with amyloid and tau pathology, as well as its potential to predict brain atrophy, cognition, and amyloid accumulation. Methods CSF NfL concentration was measured in 221 participants from the Australian Imaging, Biomarkers & Lifestyle Flagship Study of Ageing (AIBL). Results CSF NfL levels as well as NfL/amyloid β (Aβ42) were significantly elevated in AD compared to healthy controls (HC; P < .001), and in mild cognitive impairment (MCI) compared to HC (P = .008 NfL; P < .001 NfL/Aβ42). CSF NfL and NfL/Aβ42 differentiated AD from HC with an area under the receiver operating characteristic (ROC) curve (AUC) of 0.84 and 0.90, respectively. CSF NfL and NfL/Aβ42 predicted cortical amyloid load, brain atrophy, and cognition. Discussion CSF NfL is a biomarker of neurodegeneration, correlating with cognitive impairment and brain neuropathology.

The untargeted discovery and replication of a blood protein panel shows promise for predicting preclinical Alzheimer’s disease., A blood-based assessment of preclinical disease would have huge potential in the enrichment of participants for Alzheimer’s disease (AD) therapeutic trials. In this study, cognitively unimpaired individuals from the AIBL and KARVIAH cohorts were defined as Aβ negative or Aβ positive by positron emission tomography. Nontargeted proteomic analysis that incorporated peptide fractionation and high-resolution mass spectrometry quantified relative protein abundances in plasma samples from all participants. A protein classifier model was trained to predict Aβ-positive participants using feature selection and machine learning in AIBL and independently assessed in KARVIAH. A 12-feature model for predicting Aβ-positive participants was established and demonstrated high accuracy (testing area under the receiver operator characteristic curve = 0.891, sensitivity = 0.78, and specificity = 0.77). This extensive plasma proteomic study has unbiasedly highlighted putative and novel candidates for AD pathology that should be further validated with automated methodologies.

Introduction For early detection of Alzheimer's disease (AD), the field needs biomarkers that can be used to detect disease status with high sensitivity and specificity. Apolipoprotein J (ApoJ, also known as clusterin) has long been associated with AD pathogenesis through various pathways. The aim of this study was to investigate the potential of plasma apoJ as a blood biomarker for AD. Methods Using the Australian Imaging, Biomarkers and Lifestyle (AIBL) study of aging, the present study assayed plasma apoJ levels over baseline and 18 months in 833 individuals. Plasma ApoJ levels were analyzed with respect to clinical classification, age, gender, apolipoprotein E (APOE) ε4 allele status, mini‐mental state examination score, plasma amyloid beta (Aβ), neocortical Aβ burden (as measured by Pittsburgh compound B‐positron emission tomography), and total adjusted hippocampus volume. Results ApoJ was significantly higher in both mild cognitive impairment (MCI) and AD groups as compared with healthy controls (HC; P

Alzheimer’s Disease (AD) is the most common form of dementia, characterised by extracellular amyloid deposition as plaques and intracellular neurofibrillary tangles of tau protein. As no current clinical test can diagnose individuals at risk of developing AD, the aim of this project is to evaluate a blood-based biomarker panel to identify individuals who carry this risk. We analysed the levels of 22 biomarkers in clinically classified healthy controls (HC), mild cognitive impairment (MCI) and Alzheimer’s participants from the well characterised Australian Imaging, Biomarker and Lifestyle (AIBL) study of aging. High levels of IL-10 and IL-12/23p40 were significantly associated with amyloid deposition in HC, suggesting that these two biomarkers might be used to detect at risk individuals. Additionally, other biomarkers (Eotaxin-3, Leptin, PYY) exhibited altered levels in AD participants possessing the APOE ε4 allele. This suggests that the physiology of some potential biomarkers may be altered in AD due to the APOE ε4 allele, a major risk factor for AD. Taken together, these data highlight several potential biomarkers that can be used in a blood-based panel to allow earlier identification of individuals at risk of developing AD and/or early stage AD for which current therapies may be more beneficial.

AbstarctGlaucoma is a chronic disease that shares many similarities with other neurodegenerative disorders of the central nervous system. This study was designed to evaluate the association between glaucoma and other neurodegenerative disorders by investigating glaucoma-associated protein changes in the retina and vitreous humour. The multiplexed Tandem Mass Tag based proteomics (TMT-MS3) was carried out on retinal tissue and vitreous humour fluid collected from glaucoma patients and age-matched controls followed by functional pathway and protein network interaction analysis. About 5000 proteins were quantified from retinal tissue and vitreous fluid of glaucoma and control eyes. Of the differentially regulated proteins, 122 were found linked with pathophysiology of Alzheimer’s disease (AD). Pathway analyses of differentially regulated proteins indicate defects in mitochondrial oxidative phosphorylation machinery. The classical complement pathway associated proteins were activated in the glaucoma samples suggesting an innate inflammatory response. The majority of common differentially regulated proteins in both tissues were members of functional protein networks associated brain changes in AD and other chronic degenerative conditions. Identification of previously reported and novel pathways in glaucoma that overlap with other CNS neurodegenerative disorders promises to provide renewed understanding of the aetiology and pathogenesis of age related neurodegenerative diseases.

Amyloids are fibrous proteins aggregated into toxic forms that are implicated in several chronic disorders. More than 30 diseases show deposition of fibrous amyloid proteins associated with cell loss and degeneration in the affected tissues. Evidence demonstrates that amyloid diseases result from protein aggregation or impaired amyloid clearance, but the connection between amyloid accumulation and tissue degeneration is not clear. Common examples of amyloid diseases are Alzheimer’s disease (AD), Parkinson’s disease (PD) and tauopathies, which are the most common forms of neurodegenerative diseases, as well as polyglutamine disorders and certain peripheral metabolic diseases. In these diseases, increased accumulation of toxic amyloid proteins is suspected to be one of the main causative factors in the disease pathogenesis. It is therefore important to more clearly understand how these toxic amyloid proteins accumulate as this will aide in the development of more effective preventive and therapeutic strategies. Protein homeostasis, or proteostasis, is maintained by multiple cellular pathways—including protein synthesis, quality control, and clearance—which are collectively responsible for preventing protein misfolding or aggregation. Modulating protein degradation is a very complex but attractive treatment strategy used to remove amyloid and improve cell survival. This review will focus on autophagy, an important clearance pathway of amyloid proteins, and strategies for using it as a potential therapeutic target for amyloid diseases. The physiological role of autophagy in cells, pathways for its modulation, its connection with apoptosis, cell models and caveats in developing autophagy as a treatment and as a biomarker is discussed.

It is known that apolipoprotein E (ApoE) is essential for normal lipid metabolism. ApoE is the major apolipoprotein in the central nervous system and plays a key role in neurobiology by mediating the transport of cholesterol, phospholipids, and sulfatides. We therefore examined APOE epsilon2, epsilon3, and epsilon4 knock-in mice, using electrospray ionization mass spectrometry to determine if APOE genotype or age leads to altered levels in the brain of a number of glycerophospholipids (phosphatidylinositol, PI; phosphatidylethanolamine, PE; phosphatidic acid, PA, phosphatidylserine, PS; phosphatidylcholine, PC), sphingolipids (sphingomyelin, SM; ceramide, Cer), cholesterol, and triacylglycerols. We observed slight changes within individual PI, PE, PC, Cer, and SM lipid levels in APOE epsilon2 and epsilon4 mice compared to APOE epsilon3 mice. However, overall, we did not observe any major effects in APOE epsilon4 knock-in mice for the levels of the glycerophospholipids measured, as compared to APOE epsilon2 and epsilon3 mice. Our findings indicate that variations in ApoE isoforms do not per se affect bulk lipid homeostasis in the brain. These findings indicate that APOE epsilon4 is not associated with disturbances in brain sterol or sphingolipids in the absence of environmental factors.

Introduction Alzheimer’s disease (AD) is a growing socioeconomic problem worldwide. Early diagnosis and prevention of this devastating disease have become a research priority. Consequently, the identification of clinically significant and sensitive blood biomarkers for its early detection is very important. Apolipoprotein E (APOE) is a well-known and established genetic risk factor for late-onset AD; however, the impact of the protein level on AD risk is unclear. We assessed the utility of plasma ApoE protein as a potential biomarker of AD in the large, well-characterised Australian Imaging, Biomarkers and Lifestyle Study of Ageing (AIBL) cohort. Methods Total plasma ApoE levels were measured at 18-month follow-up using a commercial bead-based enzyme-linked immunosorbent assay: the Luminex xMAP human apolipoprotein kit. ApoE levels were then analysed between clinical classifications (healthy controls, mild cognitive impairment (MCI) and AD) and correlated with the data available from the AIBL cohort, including but not limited to APOE genotype and cerebral amyloid burden. Results A significant decrease in ApoE levels was found in the AD group compared with the healthy controls. These results validate previously published ApoE protein levels at baseline obtained using different methodology. ApoE protein levels were also significantly affected, depending on APOE genotypes, with ε2/ε2 having the highest protein levels and ε4/ε4 having the lowest. Plasma ApoE levels were significantly negatively correlated with cerebral amyloid burden as measured by neuroimaging. Conclusions ApoE is decreased in individuals with AD compared with healthy controls at 18-month follow-up, and this trend is consistent with our results published at baseline. The influence of APOE genotype and sex on the protein levels are also explored. It is clear that ApoE is a strong player in the aetiology of this disease at both the protein and genetic levels.

High fat diets and sedentary lifestyles are becoming major concerns for Western countries. They have led to a growing incidence of obesity, dyslipidemia, high blood pressure, and a condition known as the insulin-resistance syndrome or metabolic syndrome. These health conditions are well known to develop along with, or be precursors to atherosclerosis, cardiovascular disease, and diabetes. Recent studies have found that most of these disorders can also be linked to an increased risk of Alzheimer's disease (AD). To complicate matters, possession of one or more apolipoprotein E epsilon4 (APOE epsilon4) alleles further increases the risk or severity of many of these conditions, including AD. ApoE has roles in cholesterol metabolism and Abeta clearance, both of which are thought to be significant in AD pathogenesis. The apparent inadequacies of ApoE epsilon4 in these roles may explain the increased risk of AD in subjects carrying one or more APOE epsilon4 alleles. This review describes some of the physiological and biochemical changes that the above conditions cause, and how they are related to the risk of AD. A diversity of topics is covered, including cholesterol metabolism, glucose regulation, diabetes, insulin, ApoE function, amyloid precursor protein metabolism, and in particular their relevance to AD. It can be seen that abnormal lipid, cholesterol and glucose metabolism are consistently indicated as central in the pathophysiology, and possibly the pathogenesis of AD. As diagnosis of mild cognitive impairment and early AD are becoming more reliable, and as evidence is accumulating that health conditions such as diabetes, obesity, and coronary artery disease are risk factors for AD, appropriate changes to diets and lifestyles will likely reduce AD risk, and also improve the prognosis for people already suffering from such conditions.

Human immunodeficiency virus type 1 (HIV-1)-associated dementia is observed in 20 –30% of patients with acquired immunodeficiency syndrome (AIDS). The 4 allele of the apolipoprotein E (APOE) gene currently is thought to play a role as a risk factor for the development of HIV dementia. The HIV protein Tat is neurotoxic and binds to the same receptor as apoE, the low-density lipoprotein receptorrelated protein (LRP). In this study, we investigated the role apoE plays in Tat toxicity. Synaptosomes from wild-type mice treated with Tat had increased reactive oxygen species (ROS), increased lipid and protein oxidation, and decreased mitochondrial membrane potential. Synaptosomes from APOE-knockout mice also had increased ROS, increased protein oxidation, and decreased mitochondrial membrane potential, but to a significantly lesser degree. Treatment of synaptosomes with heparinase and Tat increased Tat-induced oxidative stress, consistent with the notion of Tat requiring interaction with neuronal membranes to induce oxidative damage. Human lipidated apoE3 greatly protected neurons from Tat-induced toxicity, whereas human lipidated apoE4 showed no protection. We demonstrated that human apoE3 has antioxidant properties against Tat-induced toxicity. Taken together, the data suggest that murine apoE and human apoE4 act similarly and do not protect the cell from Tat-induced toxicity. This would allow excess Tat to remain outside the cell and interact with synaptosomal membranes, leading to oxidative stress and neurotoxicity, which could contribute to dementia associated with HIV. We show that the antioxidant properties of apoE3 greatly outweigh the competition for clearance in deterring Tat-induced oxidative stress. © 2004 Wiley-Liss, Inc.

Background It is unclear whether altered expression of a specific isoform of apolipoprotein E (apoE) is associated with the pathology of schizophrenia. Methods To address whether apoE may be involved in the pathology of schizophrenia, we measured the genotypic and allelic frequency of polymorphisms in its gene and transcriptional regulatory region in DNA from Brodmann’s area (BA) 9 obtained postmortem from schizophrenic and control subjects as well as its levels in the same tissue using Western blot analysis. Results The genotypic or allelic frequencies of any polymorphism studied did not vary between diagnostic cohorts. There was a significant increase in the levels of apoE protein in BA 9 from the schizophrenic subjects (Mean ± SEM: 270 ± 8.3 vs. 238 ± 7.1 ng apoE/mg protein, p = .008) and a decrease in tissue from an analogous cortical region from rats treated with haloperidol compared with vehicle-treated animals (50 ± 6.4 vs. 116 ± 9.2 ng apoE/mg protein; p = .0002). Conclusions These data support the hypothesis that increased levels of apoE may be associated with the pathology of schizophrenia and that antipsychotic drugs decrease apoE levels as part of their therapeutic actions.

Clinical studies have shown that the antioxidant vitamin E can slow the progression of Alzheimer's disease (AD). Other antioxidants reported to affect cognitive function include ginkgo biloba, vitamin C, and lipoic acid. To examine the effects of combination antioxidant therapy (CAT) on longevity and neuropathology in mice, we supplemented the diet of ApoE-deficient mice with vitamin E, ginkgo biloba, pycnogenol, and ascorbyl palmitate. ApoE-deficient mice normally exhibit increased numbers of PAS-positive inclusion bodies with aging. However, supplementation with CAT resulted in a significant increase in life span and a marked reduction of inclusion body histopathology in the hippocampus. In addition, while untreated apoE-deficient mice exhibited increased levels of TUNEL staining, a marker of DNA fragmentation, supplementation with CAT resulted in a significant reduction in the levels of TUNEL staining. These findings suggest that oxidative mechanisms, perhaps related to neuronal apoptosis, are integral to inclusion body formation in aging mice. The association between the reduced number of apoptotic cells and the reduction in inclusion bodies may explain in part the increased longevity of mice fed CAT, and supports the contention that the combined actions of selected antioxidants may be therapeutically effective against neurodegenerative diseases.

Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The epsilon4 allele of APOE is one of three (epsilon2 epsilon3 and epsilon4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the epsilon 4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOE epsilon4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the epsilon2/epsilon3/epsilon4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the epsilon2/epsilon3/epsilon4 locus.

The relationship between amyloid-beta protein (Abeta) metabolism and Alzheimer's disease is currently poorly understood. While it is well known that the generation of Abeta results from enzymatic cleavage of its parent molecule, the amyloid beta protein precursor (AbetaPP), there is little information available regarding its in vivo clearance. The E4 isoform of apolipoprotein E (apoE) has been associated with poor clearance of Abeta under in vitro conditions. This is thought to be due to its poor ability to bind Abeta compared with the other common isoforms, apoE2 and apoE3. Although cell culture studies support the notion that Abeta clearance depends upon apoE isoform, validation of these findings requires Abeta clearance studies in vivo. In this study, we examined the clearance of Abeta in vivo from the periphery in mice that expressed apoE (C57BL/6J) or lacked apoE (APOE knockout). We measured the clearance of peripherally injected Abeta over time and additionally, the quantities sequestered by peripheral organs. Western blot analysis of the murine plasma indicated that the half-life of Abeta in the periphery was approximately 15 minutes. The livers of the C57BL/6J mice were found to have sequestered approximately 40% of the total injected Abeta at 90 minutes post-injection, whilst their kidneys contained 5% of the total injected Abeta. In contrast, the livers and kidneys of the APOE knockout animals were found to contain no detectable Abeta. These findings indicate that Abeta is rapidly removed from the plasma by murine peripheral tissues and the rate of its clearance is affected by apoE.

The epsilon4 allele of apolipoprotein E (APOE) is currently the major genetic risk factor identified for Alzheimer's disease (AD). Previous in vivo data from our laboratory has demonstrated that amyloid-beta (Abeta) is rapidly removed from the plasma by the liver and kidney and that the rate of its clearance is affected by ApoE in C57BL/6J and APOE-/- mice. To expand upon these findings, we assessed the peripheral clearance of human synthetic Abeta42 in APOE epsilon2, epsilon3, and epsilon4 knock-in and APOE knock-out mice injected with lipidated recombinant apoE2, E3, and E4 protein. Our results show that APOE does influence the rate at which the mice are able to clear Abeta42 from their bloodstream. Both APOE epsilon4 mice and APOE knock-out mice treated with lipidated recombinant apoE4 demonstrated increased retention of plasma Abeta42 over time compared to APOE epsilon2/APOE knock-out rE2 and APOE epsilon3/APOE knock-out rE3 mice. These findings suggest that the peripheral clearance of Abeta42 is significantly altered by APOE genotype. Given that APOE epsilon4 is a risk factor for AD, then these novel findings provide some insight into the role of ApoE isoforms on the peripheral clearance of Abeta which may impact on clearance from the brain.

It is known that apolipoprotein E (ApoE) is essential for normal lipid metabolism. ApoE is the major apolipoprotein in the central nervous system and plays a key role in neurobiology by mediating the transport of cholesterol, phospholipids, and sulfatides. We therefore examined APOE epsilon2, epsilon3, and epsilon4 knock-in mice, using electrospray ionization mass spectrometry to determine if APOE genotype or age leads to altered levels in the brain of a number of glycerophospholipids (phosphatidylinositol, PI; phosphatidylethanolamine, PE; phosphatidic acid, PA, phosphatidylserine, PS; phosphatidylcholine, PC), sphingolipids (sphingomyelin, SM; ceramide, Cer), cholesterol, and triacylglycerols. We observed slight changes within individual PI, PE, PC, Cer, and SM lipid levels in APOE epsilon2 and epsilon4 mice compared to APOE epsilon3 mice. However, overall, we did not observe any major effects in APOE epsilon4 knock-in mice for the levels of the glycerophospholipids measured, as compared to APOE epsilon2 and epsilon3 mice. Our findings indicate that variations in ApoE isoforms do not per se affect bulk lipid homeostasis in the brain. These findings indicate that APOE epsilon4 is not associated with disturbances in brain sterol or sphingolipids in the absence of environmental factors.