Hypercholesterolemia accelerates the Alzheimer's amyloid pathology in a transgenic mouse model

Liver as a new target organ in Alzheimer's disease: insight from cholesterol metabolism and its role in amyloid-beta clearance

Alzheimer's disease, the primary cause of dementia, is characterized by neuropathologies, such as amyloid plaques, synaptic and neuronal degeneration, and neurofibrillary tangles. Although amyloid plaques are the primary characteristic of Alzheimer's disease in the central nervous system and peripheral organs, targeting amyloid-beta clearance in the central nervous system has shown limited clinical efficacy in Alzheimer's disease treatment. Metabolic abnormalities are commonly observed in patients with Alzheimer's disease. The liver is the primary peripheral organ involved in amyloid-beta metabolism, playing a crucial role in the pathophysiology of Alzheimer's disease. Notably, impaired cholesterol metabolism in the liver may exacerbate the development of Alzheimer's disease. In this review, we explore the underlying causes of Alzheimer's disease and elucidate the role of the liver in amyloid-beta clearance and cholesterol metabolism. Furthermore, we propose that restoring normal cholesterol metabolism in the liver could represent a promising therapeutic strategy for addressing Alzheimer's disease.

Cholesterol profiling reveals 7β-hydroxycholesterol as a pathologically relevant peripheral biomarker of Alzheimer's disease

AIM

Cholesterol homeostasis is associated with Alzheimer's disease (AD). Despite the multitude of cholesterol metabolites, little is known about which metabolites are directly involved in AD pathogenesis and can serve as its potential biomarkers.

METHODS

To identify "hit" metabolites, steroid profiling was conducted in mice with different age, diet, and genotype and also in humans with normal cognition, mild cognitive impairment, and AD using gas chromatography-mass spectrometry. Then, using one of the "hit" molecules (7β-hydroxycholesterol; OHC), molecular and histopathological experiment and behavioral testing were conducted in normal mice following its intracranial stereotaxic injection to see whether this molecule drives AD pathogenesis and causes cognitive impairment.

RESULTS

The serum levels of several metabolites, including 7β-OHC, were increased by aging in the 3xTg-AD unlike normal mice. Consistently, the levels of 7β-OHC were increased in the hairs of patients with AD and were correlated with clinical severity. We found that 7β-OHC directly affects AD-related pathophysiology; intrahippocampal injection of 7β-OHC induced astrocyte and microglial cell activation, increased the levels of pro-inflammatory cytokines (TNF-alpha, IL-1β, IL-6), and enhanced amyloidogenic pathway. Mice treated with 7β-OHC also exhibited deficits in memory and frontal/executive functions assessed by object recognition and 5-choice serial reaction time task, respectively.

CONCLUSIONS

Our results suggest that 7β-OHC could serve as a convenient, peripheral biomarker of AD. As directly involved in AD pathogenesis, 7β-OHC assay may help actualize personalized medicine in a way to identify an at-risk subgroup as a candidate population for statin-based AD treatment.

Cholesterol and Lipid Rafts in the Biogenesis of Amyloid-β Protein and Alzheimer's Disease

Cholesterol has been conjectured to be a modulator of the amyloid cascade, the mechanism that produces the amyloid-β (Aβ) peptides implicated in the onset of Alzheimer's disease. We propose that cholesterol impacts the genesis of Aβ not through direct interaction with proteins in the bilayer, but indirectly by inducing the liquid-ordered phase and accompanying liquid-liquid phase separations, which partition proteins in the amyloid cascade to different lipid domains and ultimately to different endocytotic pathways. We explore the full process of Aβ genesis in the context of liquid-ordered phases induced by cholesterol, including protein partitioning into lipid domains, mechanisms of endocytosis experienced by lipid domains and secretases, and pH-controlled activation of amyloid precursor protein secretases in specific endocytotic environments. Outstanding questions on the essential role of cholesterol in the amyloid cascade are identified for future studies.

Current View on PPAR-α and Its Relation to Neurosteroids in Alzheimer's Disease and Other Neuropsychiatric Disorders: Promising Targets in a Therapeutic Strategy

Peroxisome proliferator-activated receptors (PPARs) may play an important role in the pathomechanism/pathogenesis of Alzheimer's disease (AD) and several other neurological/neuropsychiatric disorders. AD leads to progressive alterations in the redox state, ion homeostasis, lipids, and protein metabolism. Significant alterations in molecular processes and the functioning of several signaling pathways result in the degeneration and death of synapses and neuronal cells, leading to the most severe dementia. Peroxisome proliferator-activated receptor alpha (PPAR-α) is among the processes affected by AD; it regulates the transcription of genes related to the metabolism of cholesterol, fatty acids, other lipids and neurotransmission, mitochondria biogenesis, and function. PPAR-α is involved in the cholesterol transport to mitochondria, the substrate for neurosteroid biosynthesis. PPAR-α-coding enzymes, such as sulfotransferases, which are responsible for neurosteroid sulfation. The relation between PPAR-α and cholesterol/neurosteroids may have a significant impact on the course and progression of neurodegeneration/neuroprotection processes. Unfortunately, despite many years of intensive studies, the pathogenesis of AD is unknown and therapy for AD and other neurodegenerative diseases is symptomatic, presenting a significant goal and challenge today. This review presents recent achievements in therapeutic approaches for AD, which are targeting PPAR-α and its relation to cholesterol and neurosteroids in AD and neuropsychiatric disorders.

Altering plasma lipids and liver enzyme activities via hippocampal injections of hen Lysozyme amyloid aggregates in an Alzheimer's disease mouse model: Insights into the therapeutic role of Bis (Indolyl) phenylmethane

Alzheimer's disease (AD) is a prevalent form of dementia in the elderly. There is currently no effective treatment available for this disease. Diagnosis of AD typically relies on clinical manifestations and specific biomarkers. The present study investigated the impact of inducing Alzheimer's disease (AD) in mice through the injection of lysozyme amyloids formed in the presence or absence of Bis (Indolyl) phenylmethane (BIPM) on alterations in plasma lipid profiles and liver enzyme activities. 24 adult Wistar rats were divided into control, Scopolamine, Lysozyme, BIPM groups and the blood samples were obtained from the groups for biochemical analysis. The findings of the study revealed significant changes in the plasma lipid profiles and liver enzyme markers of the Lysozyme group compared to the control group. The Lysozyme group exhibited elevated triglycerides (n = 6, P < 0.02) and LDL levels (n = 6, P < 0.02), reduced HDL (n = 6, P < 0.05) and cholesterol levels (n = 6, P < 0.02), and altered serum glutamic oxaloacetic transaminase (SGOT) level (n = 6, P < 0.05) compared to controls. While the level of serum glutamic pyruvic transaminase (SGPT) did not change significantly compared to the control. BIPM groups showed no significant changes in lipid or enzyme levels compared to controls. Overall, our research has shown that BIPM has the ability to modify the structure of HEWL aggregates, thereby improving the detrimental effects associated with AD caused by these aggregates. Analyzing lipid profiles and liver enzyme markers presents a promising avenue for targeted therapeutic approaches. These alterations observed in the plasma may potentially serve as candidate biomarkers for diagnosing this disease.

Temporal Characterization of the Amyloidogenic APPswe/PS1dE9;hAPOE4 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a devastating disorder with a global prevalence estimated at 55 million people. In clinical studies administering certain anti-beta-amyloid (Aβ) antibodies, amyloid-related imaging abnormalities (ARIAs) have emerged as major adverse events. The frequency of these events is higher among apolipoprotein ε4 allele carriers (APOE4) compared to non-carriers. To reflect patients most at risk for vascular complications of anti-Aβ immunotherapy, we selected an APPswe/PS1dE9 transgenic mouse model bearing the human APOE4 gene (APPPS1:E4) and compared it with the same APP/PS1 mouse model bearing the human APOE3 gene (APOE ε3 allele; APPPS1:E3). Using histological and biochemical analyses, we characterized mice at three ages: 8, 12, and 16 months. Female and male mice were assayed for general cerebral fibrillar and pyroglutamate (pGlu-3) Aβ deposition, cerebral amyloid angiopathy (CAA), microhemorrhages, apoE and cholesterol composition, astrocytes, microglia, inflammation, lysosomal dysfunction, and neuritic dystrophy. Amyloidosis, lipid deposition, and astrogliosis increased with age in APPPS1:E4 mice, while inflammation did not reveal significant changes with age. In general, APOE4 carriers showed elevated Aβ, apoE, reactive astrocytes, pro-inflammatory cytokines, microglial response, and neuritic dystrophy compared to APOE3 carriers at different ages. These results highlight the potential of the APPPS1:E4 mouse model as a valuable tool in investigating the vascular side effects associated with anti-amyloid immunotherapy.

A randomized feasibility trial of the modified Atkins diet in older adults with mild cognitive impairment due to Alzheimer's disease

Background

Alzheimer's disease (AD) is increasing in prevalence, but effective treatments for its cognitive impairment remain severely limited. This study investigates the impact of ketone body production through dietary manipulation on memory in persons with mild cognitive impairment due to early AD and explores potential mechanisms of action.

Methods

We conducted a 12-week, parallel-group, controlled feasibility trial of a ketogenic diet, the modified Atkins diet (MAD), compared to a control diet in patients with cognitive impairments attributed to AD. We administered neuropsychological assessments, including memory tests, and collected blood samples at baseline and after 12 weeks of intervention. We performed untargeted lipidomic and targeted metabolomic analyses on plasma samples to detect changes over time.

Results

A total of 839 individuals were screened to yield 38 randomized participants, with 20 assigned to receive MAD and 18 assigned to receive a control diet. Due to attrition, only 13 in the MAD arm and nine in the control arm were assessed for the primary endpoint, with two participants meeting ketosis levels used to define MAD adherence criteria. The average change from baseline in the Memory Composite Score was 1.37 (95% CI: -0.87, 4.90) points higher in the MAD group compared to the control group. The effect size of the intervention on baseline MAD change was moderate (Cohen's D = 0.57, 95% CI: -0.67, 1.33). In the 15 participants (nine MAD, six control) assessed for lipidomic and metabolomic-lipidomics and metabolomics, 13 metabolites and 10 lipids showed significant changes from baseline to 12 weeks, including triacylglycerols (TAGs, 50:5, 52:5, and 52:6), sphingomyelins (SM, 44:3, 46:0, 46:3, and 48:1), acetoacetate, fatty acylcarnitines, glycerol-3-phosphate, and hydroxy fatty acids.

Conclusions

Attrition was greatest between baseline and week 6. All participants retained at week 6 completed the study. Despite low rates of adherence by criteria defined a priori, lipidomic and metabolomic analyses indicate significant changes from baseline in circulating lipids and metabolites between MAD and control participants at 12-week postrandomization, and MAD participants showed greater, albeit nonsignificant, improvement in memory.

Maternal history of Alzheimer's disease predisposes to altered serum cholesterol levels in adult offspring

Controversial findings regarding the association between serum cholesterol levels and Alzheimer's disease (AD) have been identified through observational studies. The genetic basis shared by both factors and the causality between them remain largely unknown. The objective of this study is to examine the causal impact of maternal history of AD on changes in serum cholesterol levels in adult offspring. By retrieving genetic variants from summary statistics of large-scale genome-wide association study of maternal history of AD (European-based: Ncase = 27 696, Ncontrol = 260 980). The causal association between genetically predicted maternal history of AD and changes in serum cholesterol levels in adult offspring was examined using the two-sample Mendelian randomization (MR) method. Causal impact estimates were calculated using single-nucleotide polymorphisms in both univariable MR (UMR) and multivariable MR (MVMR) analyses. Additionally, other approaches, such as Cochran's Q test and leave-one-out variant analysis, were employed to correct for potential biases. The results of UMR presented that genetically predicted maternal history of AD was positively associated with hypercholesterolemia (OR = 1.014; 95% CI: 1.009-1.018; p < 0.001), total cholesterol (OR = 1.29; 95% CI: 1.134-1.466; p < 0.001) and low-density lipoprotein (OR = 1.525; 95% CI: 1.272-1.828; p < 0.001) among adult offspring. Genetic predisposition for maternal history of AD to be negatively associated with high-density lipoprotein (OR = 0.889; 95% CI: 0.861-0.917; p < 0.001). The MVMR analysis remained robust and significant after adjusting for diabetes and obesity in offspring. Sufficient evidence was provided in this study to support the putative causal impact of maternal history of AD on the change of serum cholesterol profile in adult offspring. In clinical practice, priority should be given to the detection and monitoring of cholesterol levels in individuals with a maternal history of AD, particularly in the early stages.

Impact of micronutrients and nutraceuticals on cognitive function and performance in Alzheimer's disease

Alzheimer's disease (AD) is a major global health problem today and is the most common form of dementia. AD is characterized by the formation of β-amyloid (Aβ) plaques and neurofibrillary clusters, leading to decreased brain acetylcholine levels in the brain. Another mechanism underlying the pathogenesis of AD is the abnormal phosphorylation of tau protein that accumulates at the level of neurofibrillary aggregates, and the areas most affected by this pathological process are usually the cholinergic neurons in cortical, subcortical, and hippocampal areas. These effects result in decreased cognitive function, brain atrophy, and neuronal death. Malnutrition and weight loss are the most frequent manifestations of AD, and these are also associated with greater cognitive decline. Several studies have confirmed that a balanced low-calorie diet and proper nutritional intake may be considered important factors in counteracting or slowing the progression of AD, whereas a high-fat or hypercholesterolemic diet predisposes to an increased risk of developing AD. Especially, fruits, vegetables, antioxidants, vitamins, polyunsaturated fatty acids, and micronutrients supplementation exert positive effects on aging-related changes in the brain due to their antioxidant, anti-inflammatory, and radical scavenging properties. The purpose of this review is to summarize some possible nutritional factors that may contribute to the progression or prevention of AD, understand the role that nutrition plays in the formation of Aβ plaques typical of this neurodegenerative disease, to identify some potential therapeutic strategies that may involve some natural compounds, in delaying the progression of the disease.

Current Perspectives: Obesity and Neurodegeneration - Links and Risks

Obesity is increasing in prevalence across all age groups. Long-term obesity can lead to the development of metabolic and cardiovascular diseases through its effects on adipose, skeletal muscle, and liver tissue. Pathological mechanisms associated with obesity include immune response and inflammation as well as oxidative stress and consequent endothelial and mitochondrial dysfunction. Recent evidence links obesity to diminished brain health and neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD). Both AD and PD are associated with insulin resistance, an underlying syndrome of obesity. Despite these links, causative mechanism(s) resulting in neurodegenerative disease remain unclear. This review discusses relationships between obesity, AD, and PD, including clinical and preclinical findings. The review then briefly explores nonpharmacological directions for intervention.

Associations of dietary cholesterol and fat, blood lipids, and risk for dementia in older women vary by APOE genotype

INTRODUCTION

Whether apolipoprotein E's (APOE's) involvement in lipid metabolism contributes to Alzheimer's disease (AD) risk remains unknown.

METHODS

Incident probable dementia and cognitive impairment (probable dementia+mild cognitive impairment) were analyzed in relation to baseline serum lipids (total, low-density lipoprotein [LDL], high-density lipoprotein [HDL], non-HDL cholesterol, total-to-HDL, LDL-to-HDL, remnant cholesterol, and triglycerides) using Mendelian randomization in 5358 postmenopausal women from the Women's Health Initiative Memory Study. We also examined associations of baseline dietary cholesterol and fat with lipids based on APOE status.

RESULTS

After an average of 11.13 years, less favorable lipid levels related to greater dementia and cognitive impairment risk. Dementia (odds ratio [OR] = 3.13; 95% confidence interval [CI]: 2.31 to 4.24) and cognitive impairment (OR = 2.38; 95% CI: 1.85 to 3.06) risk were greatest in relation to higher remnant cholesterol levels. Greater cholesterol consumption related to poorer lipids in APOE4+ compared to APOE3 carriers.

DISCUSSION

APOE4+ carriers consuming more cholesterol had less favorable lipids, which were associated with greater dementia and cognitive impairment risk.

HIGHLIGHTS

Less favorable serum lipids were associated with higher dementia incidence. Mendelian randomization findings suggest causality between lipids and dementia. Lipid levels in older women may be clinical indicators of dementia risk. APOE4 carriers had poorest lipid profiles in relation to cholesterol consumption. APOE risk for dementia may be modifiable through lipid management.

Sterol-activated amyloid beta fibril formation

The metabolic processes that link Alzheimer's disease (AD) to elevated cholesterol levels in the brain are not fully defined. Amyloid beta (Aβ) plaque accumulation is believed to begin decades prior to symptoms and to contribute significantly to the disease. Cholesterol and its metabolites accelerate plaque formation through as-yet-undefined mechanisms. Here, the mechanism of cholesterol (CH) and cholesterol 3-sulfate (CS) induced acceleration of Aβ42 fibril formation is examined in quantitative ligand binding, Aβ42 fibril polymerization, and molecular dynamics studies. Equilibrium and pre-steady-state binding studies reveal that monomeric Aβ42•ligand complexes form and dissociate rapidly relative to oligomerization, that the ligand/peptide stoichiometry is 1-to-1, and that the peptide is likely saturated in vivo. Analysis of Aβ42 polymerization progress curves demonstrates that ligands accelerate polymer synthesis by catalyzing the conversion of peptide monomers into dimers that nucleate the polymerization reaction. Nucleation is accelerated ∼49-fold by CH, and ∼13,000-fold by CS - a minor CH metabolite. Polymerization kinetic models predict that at presumed disease-relevant CS and CH concentrations, approximately half of the polymerization nuclei will contain CS, small oligomers of neurotoxic dimensions (∼12-mers) will contain substantial CS, and fibril-formation lag times will decrease 13-fold relative to unliganded Aβ42. Molecular dynamics models, which quantitatively predict all experimental findings, indicate that the acceleration mechanism is rooted in ligand-induced stabilization of the peptide in non-helical conformations that readily form polymerization nuclei.

The Effect of Fat Intake with Increased Omega-6-to-Omega-3 Polyunsaturated Fatty Acid Ratio in Animal Models of Early and Late Alzheimer's Disease-like Pathogenesis

This work aims to clarify the effect of dietary polyunsaturated fatty acid (PUFA) intake on the adult brain affected by amyloid pathology. McGill-R-Thy1-APP transgenic (Tg) rat and 5xFAD Tg mouse models that represent earlier or later disease stages were employed. The animals were exposed to a control diet (CD) or an HFD based on corn oil, from young (rats) or adult (mice) ages for 24 or 10 weeks, respectively. In rats and mice, the HFD impaired reference memory in wild-type (WT) animals but did not worsen it in Tg, did not cause obesity, and did not increase triglycerides or glucose levels. Conversely, the HFD promoted stronger microglial activation in Tg vs. WT rats but had no effect on cerebral amyloid deposition. IFN-γ, IL-1β, and IL-6 plasma levels were increased in Tg rats, regardless of diet, while CXCL1 chemokine levels were increased in HFD-fed mice, regardless of genotype. Hippocampal 3-nitrotyrosine levels tended to increase in HFD-fed Tg rats but not in mice. Overall, an HFD with an elevated omega-6-to-omega-3 ratio as compared to the CD (25:1 vs. 8.4:1) did not aggravate the outcome of AD regardless of the stage of amyloid pathology, suggesting that many neurobiological processes relevant to AD are not directly dependent on PUFA intake.

Characterizing the transmembrane domains of ADAM10 and BACE1 and the impact of membrane composition

The β-secretase, BACE1, and the α-secretase, ADAM10, are known to competitively cleave amyloid precursor protein (APP) in the amyloid cascades of Alzheimer's disease. Cleavage of APP by BACE1 produces a 99-residue C-terminal peptide (APP-C99) that is subsequently cleaved by γ-secretase to form amyloid-β (Aβ) protein, whereas cleavage of APP by ADAM10 is nonamyloidogenic. It has been speculated that ADAM10/APP and BACE1/APP interactions are regulated by colocalization within and outside of liquid-ordered membrane domains; however, the mechanism of this regulation and the character of the proteins' transmembrane domains are not well understood. In this work, we have developed and characterized minimal congener sequences for the transmembrane domains of ADAM10 and BACE1 using a multiscale modeling approach combining both temperature replica exchange and conventional molecular dynamics simulations based on the coarse-grained Martini2.2 and all-atom CHARMM36 force fields. Our results show that membrane composition impacts the character of the transmembrane domains of BACE1 and ADAM10, adding credence to the speculation that membrane domains are involved in the etiology of Alzheimer's disease.

Cholesterol-dependent amyloid β production: space for multifarious interactions between amyloid precursor protein, secretases, and cholesterol

Amyloid β is considered a key player in the development and progression of Alzheimer's disease (AD). Many studies investigating the effect of statins on lowering cholesterol suggest that there may be a link between cholesterol levels and AD pathology. Since cholesterol is one of the most abundant lipid molecules, especially in brain tissue, it affects most membrane-related processes, including the formation of the most dangerous form of amyloid β, Aβ42. The entire Aβ production system, which includes the amyloid precursor protein (APP), β-secretase, and the complex of γ-secretase, is highly dependent on membrane cholesterol content. Moreover, cholesterol can affect amyloidogenesis in many ways. Cholesterol influences the stability and activity of secretases, but also dictates their partitioning into specific cellular compartments and cholesterol-enriched lipid rafts, where the amyloidogenic machinery is predominantly localized. The most complicated relationships have been found in the interaction between cholesterol and APP, where cholesterol affects not only APP localization but also the precise character of APP dimerization and APP processing by γ-secretase, which is important for the production of Aβ of different lengths. In this review, we describe the intricate web of interdependence between cellular cholesterol levels, cholesterol membrane distribution, and cholesterol-dependent production of Aβ, the major player in AD.

Mitochondrial cholesterol: Metabolism and impact on redox biology and disease

Cholesterol is a crucial component of membrane bilayers by regulating their structural and functional properties. Cholesterol traffics to different cellular compartments including mitochondria, whose cholesterol content is low compared to other cell membranes. Despite the limited availability of cholesterol in the inner mitochondrial membrane (IMM), the metabolism of cholesterol in the IMM plays important physiological roles, acting as the precursor for the synthesis of steroid hormones and neurosteroids in steroidogenic tissues and specific neurons, respectively, or the synthesis of bile acids through an alternative pathway in the liver. Accumulation of cholesterol in mitochondria above physiological levels has a negative impact on mitochondrial function through several mechanisms, including the limitation of crucial antioxidant defenses, such as the glutathione redox cycle, increased generation of reactive oxygen species and consequent oxidative modification of cardiolipin, and defective assembly of respiratory supercomplexes. These adverse consequences of increased mitochondrial cholesterol trafficking trigger the onset of oxidative stress and cell death, and, ultimately, contribute to the development of diverse diseases, including metabolic liver diseases (i.e. fatty liver disease and liver cancer), as well as lysosomal disorders (i.e. Niemann-Pick type C disease) and neurodegenerative diseases (i.e. Alzheimer's disease). In this review, we summarize the metabolism and regulation of mitochondrial cholesterol and its potential impact on liver and neurodegenerative diseases.

Cholesterol twists the transmembrane Di-Gly region of amyloid-precursor protein

Nearly 95% of Alzheimer's disease (AD) occurs sporadically without genetic linkage. Aging, hypertension, high cholesterol content, and diabetes are known nongenomic risk factors of AD. Aggregation of Aβ peptides is an initial event of AD pathogenesis. Aβ peptides are catabolic products of a type I membrane protein called amyloid precursor protein (APP). Aβ40 is the major product, whereas the 2-residue-longer version, Aβ42, induces amyloid plaque formation in the AD brain. Since cholesterol content is one risk factor for sporadic AD, we aimed to explore whether cholesterol in the membrane affects the structure of the APP transmembrane region, thereby modulating the γ-secretase cutting behavior. Here, we synthesized several peptides containing the APP transmembrane region (sequence 693-726, corresponding to the Aβ_22-55 sequence) with one or two Cys mutations for spin labeling. We performed three electron spin resonance experiments to examine the structural changes of the peptides in liposomes composed of dioleoyl phosphatidylcholine and different cholesterol content. Our results show that cholesterol increases membrane thickness by 10% and peptide length accordingly. We identified that the di-glycine region of Aβ_36-40 (sequence VGGVV) exhibits the most profound change in response to cholesterol compared with other segments, explaining how the presence of cholesterol affects the γ-secretase cutting site. This study provides spectroscopic evidence showing how cholesterol modulates the structure of the APP transmembrane region in a lipid bilayer.

White matter injury, cholesterol dysmetabolism, and APP/Abeta dysmetabolism interact to produce Alzheimer's disease (AD) neuropathology: A hypothesis and review

We postulate that myelin injury contributes to cholesterol release from myelin and cholesterol dysmetabolism which contributes to Abeta dysmetabolism, and combined with genetic and AD risk factors, leads to increased Abeta and amyloid plaques. Increased Abeta damages myelin to form a vicious injury cycle. Thus, white matter injury, cholesterol dysmetabolism and Abeta dysmetabolism interact to produce or worsen AD neuropathology. The amyloid cascade is the leading hypothesis for the cause of Alzheimer's disease (AD). The failure of clinical trials based on this hypothesis has raised other possibilities. Even with a possible new success (Lecanemab), it is not clear whether this is a cause or a result of the disease. With the discovery in 1993 that the apolipoprotein E type 4 allele (APOE4) was the major risk factor for sporadic, late-onset AD (LOAD), there has been increasing interest in cholesterol in AD since APOE is a major cholesterol transporter. Recent studies show that cholesterol metabolism is intricately involved with Abeta (Aβ)/amyloid transport and metabolism, with cholesterol down-regulating the Aβ LRP1 transporter and upregulating the Aβ RAGE receptor, both of which would increase brain Aβ. Moreover, manipulating cholesterol transport and metabolism in rodent AD models can ameliorate pathology and cognitive deficits, or worsen them depending upon the manipulation. Though white matter (WM) injury has been noted in AD brain since Alzheimer's initial observations, recent studies have shown abnormal white matter in every AD brain. Moreover, there is age-related WM injury in normal individuals that occurs earlier and is worse with the APOE4 genotype. Moreover, WM injury precedes formation of plaques and tangles in human Familial Alzheimer's disease (FAD) and precedes plaque formation in rodent AD models. Restoring WM in rodent AD models improves cognition without affecting AD pathology. Thus, we postulate that the amyloid cascade, cholesterol dysmetabolism and white matter injury interact to produce and/or worsen AD pathology. We further postulate that the primary initiating event could be related to any of the three, with age a major factor for WM injury, diet and APOE4 and other genes a factor for cholesterol dysmetabolism, and FAD and other genes for Abeta dysmetabolism.

Correlations between the NMR Lipoprotein Profile, APOE Genotype, and Cholesterol Efflux Capacity of Fasting Plasma from Cognitively Healthy Elderly Adults

Cholesterol efflux capacity (CEC) is of interest given its potential relationship with several important clinical conditions including Alzheimer's disease. The inactivation of the APOE locus in mouse models supports the idea that it is involved in determining the CEC. With that in mind, we examine the impact of the plasma metabolome profile and the APOE genotype on the CEC in cognitively healthy elderly subjects. The study subjects were 144 unrelated healthy individuals. The plasma CEC was determined by exposing cultured mouse macrophages treated with BODIPY-cholesterol to human plasma. The metabolome profile was determined using NMR techniques. Multiple regression was performed to identify the most important predictors of CEC, as well as the NMR features most strongly associated with the APOE genotype. Plasma 3-hydroxybutyrate was the variable most strongly correlated with the CEC (r = 0.365; p = 7.3 × 10^-6). Male sex was associated with a stronger CEC (r = -0.326, p = 6.8 × 10^-5). Most of the NMR particles associated with the CEC did not correlate with the APOE genotype. The NMR metabolomics results confirmed the APOE genotype to have a huge effect on the concentration of plasma lipoprotein particles as well as those of other molecules including omega-3 fatty acids. In conclusion, the CEC of human plasma was associated with ketone body concentration, sex, and (to a lesser extent) the other features of the plasma lipoprotein profile. The APOE genotype exerted only a weak effect on the CEC via the modulation of the lipoprotein profile. The APOE locus was associated with omega-3 fatty acid levels independent of the plasma cholesterol level.

Non-Enzymatic Antioxidants against Alzheimer's Disease: Prevention, Diagnosis and Therapy

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive memory loss and cognitive decline. Although substantial research has been conducted to elucidate the complex pathophysiology of AD, the therapeutic approach still has limited efficacy in clinical practice. Oxidative stress (OS) has been established as an early driver of several age-related diseases, including neurodegeneration. In AD, increased levels of reactive oxygen species mediate neuronal lipid, protein, and nucleic acid peroxidation, mitochondrial dysfunction, synaptic damage, and inflammation. Thus, the identification of novel antioxidant molecules capable of detecting, preventing, and counteracting AD onset and progression is of the utmost importance. However, although several studies have been published, comprehensive and up-to-date overviews of the principal anti-AD agents harboring antioxidant properties remain scarce. In this narrative review, we summarize the role of vitamins, minerals, flavonoids, non-flavonoids, mitochondria-targeting molecules, organosulfur compounds, and carotenoids as non-enzymatic antioxidants with AD diagnostic, preventative, and therapeutic potential, thereby offering insights into the relationship between OS and neurodegeneration.

The relationship between midlife dyslipidemia and lifetime incidence of dementia: A systematic review and meta-analysis of cohort studies

Introduction

We conducted a systematic review and meta-analysis to review the relationship between midlife dyslipidemia and lifetime incident dementia.

Methods

The databases Medline, Embase, Scopus, Web of Science, and Cochrane were searched from inception to February 20, 2022. Longitudinal studies examining the relationship between midlife lipid levels on dementia, dementia subtypes, and/or cognitive impairment were pooled using inverse-variance weighted random-effects meta-analysis.

Results

Seventeen studies (1.2 million participants) were included. Midlife hypercholesterolemia was associated with increased incidence of mild cognitive impairment (effect size [ES] = 2.01; 95% confidence interval [CI] 1.19 to 2.84; I² = 0.0%) and all-cause dementia (ES = 1.14; 95% CI: 1.07 to 1.21; I² = 0.0%). Each 1 mmol/L increase in low-density lipoprotein was associated with an 8% increase (ES = 1.08, 95% CI: 1.03 to 1.14; I² = 0.3%) in incidence of all-cause dementia.

Discussion

Midlife dyslipidemia is associated with an increased risk of cognitive impairment in later life.

The Joint Effect of Body Mass Index and Serum Lipid Levels on Incident Dementia among Community-Dwelling Older Adults

OBJECTIVES

This study aimed to explore the joint effect of body mass index (BMI) and serum lipids levels on incident dementia.

METHODS

We prospectively followed up with 1,627 dementia-free community residents aged ≥60 for 5.7 years on average. At baseline, weight, and height were measured, and total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were detected in serum. Demographic characteristics were collected through questionnaires. Dementia was based on consensus diagnosis of neurologists and neuropsychologists using DSM-IV criteria. Additive Cox proportional model was used to assess the exposure-response relationship between BMI and serum lipid levels and dementia risk. Interactions and further classifications of BMI and serum lipid levels were further presented by bivariate surface models and decision-tree models.

RESULTS

The joint effects of TC with BMI, TG with BMI, and LDL-C with BMI on the risk of incident dementia shared a similar pattern, different from their independent exposure-response curves. The joint effect of HDL-C with BMI showed an S-surface but without statistical significance. Participants with TC<5.4 mmol/L and BMI<21 kg/m2 (Hazard Ratio(HR) 1.93, 95% Confidence Interval (CI) 1.05-3.53), TC<5.4 mmol/L and BMI≥21 kg/m2 (HR 1.73, 95% CI 1.09-2.72), and TC≥5.4 mmol/L and BMI<21 kg/m2 (HR 4.02, 95% CI 2.10-7.71) were identified to have the increased risk of incident dementia compared to those with TC≥5.4 mmol/L and BMI≥21 kg/m2. Participants with TG<1.7 mmol/L and BMI<21 kg/m2 had an increased risk of incident dementia compared to those with TG≥1.7 mmol/L and BMI≥21 kg/m2 (HR 1.98, 95%CI 1.17-3.3). Participants with LDL-C≥3.3 mmol/L and BMI<21 kg/m2 were identified to have an increased risk of incident dementia compared to those with LDL-C≥3.3 mmol/L and BMI≥21 kg/m2 (HR 3.33, 95%CI 1.64-6.78).

CONCLUSIONS

Our study showed that low BMI combined with low or high levels of serum lipids may increase the risk of dementia among older adults. This finding suggests the potential impacts of these two metabolic indexes on the risk of dementia.

Cardiovascular Risk Factors and Risk of Alzheimer Disease and Mortality: A Latent Class Approach

Background Cardiovascular risk factors co-occur with one another, and little is known about the extent of their clustering and risk of Alzheimer disease (AD). We identify groups of cardiovascular risk factors in cognitively normal individuals and investigate between-group differences in incident AD and death. Methods and Results Cognitively normal individuals were recruited from the National Alzheimer's Coordinator Center. A latent class analysis was conducted with hypertension, hypercholesterolemia, heart condition, stroke, smoking history, diabetes, and high body mass index. Between-group differences in the incidence of AD, mortality, and mortality-adjusted AD were investigated. This study included 12 412 cognitively normal individuals (average follow-up, 65 months). Three groups were identified: (1) low probabilities of cardiovascular risk factors (reference; N=5398 [43%]), (2) hypertension and hypercholesterolemia (vascular-dominant; N=5721 [46%]), and (3) hypertension, hypercholesterolemia, diabetes, and high body mass index (vascular-metabolic; N=1293 [10%]). Both vascular groups were significantly older, had more men, were slightly less educated, and were slightly more cognitively impaired than the reference group (all P<0.05). However, only the vascular-metabolic group had a significantly younger age of death compared with the reference group (84.3 versus 88.7 years, P<0.001). Only the vascular-dominant group had a greater incidence of AD (odds ratio [OR], 1.30; P<0.001) compared with the reference group. Mortality was greater in the vascular-dominant (OR, 3.26; P<0.001) and vascular-metabolic groups (OR, 1.84; P=0.02). Mortality-adjusted AD was greater in the vascular-dominant (OR, 1.54; P=0.02) and vascular-metabolic groups (OR, 1.46; P=0.04). Conclusions Three distinct cardiovascular risk factor groups were identified in cognitively normal elderly individuals. Only the vascular-dominant group was associated with a greater incidence of AD. Selective mortality may contribute to the attenuated association between the vascular-metabolic group and incident AD.

Diabetes and hypertension are related to amyloid-beta burden in the population-based Rotterdam Study

Higher vascular disease burden increases the likelihood of developing dementia, including Alzheimer's disease. Better understanding the association between vascular risk factors and Alzheimer's disease pathology at the predementia stage is critical for developing effective strategies to delay cognitive decline. In this work, we estimated the impact of six vascular risk factors on the presence and severity of in vivo measured brain amyloid-beta (Aβ) plaques in participants from the population-based Rotterdam Study. Vascular risk factors (hypertension, hypercholesterolaemia, diabetes, obesity, physical inactivity and smoking) were assessed 13 (2004-2008) and 7 years (2009-2014) prior to 18F-florbetaben PET (2018-2021) in 635 dementia-free participants. Vascular risk factors were associated with binary amyloid PET status or continuous PET readouts (standard uptake value ratios, SUVrs) using logistic and linear regression models, respectively, adjusted for age, sex, education, APOE4 risk allele count and time between vascular risk and PET assessment. Participants' mean age at time of amyloid PET was 69 years (range: 60-90), 325 (51.2%) were women and 190 (29.9%) carried at least one APOE4 risk allele. The adjusted prevalence estimates of an amyloid-positive PET status markedly increased with age [12.8% (95% CI 11.6; 14) in 60-69 years versus 35% (36; 40.8) in 80-89 years age groups] and APOE4 allele count [9.7% (8.8; 10.6) in non-carriers versus 38.4% (36; 40.8) to 60.4% (54; 66.8) in carriers of one or two risk allele(s)]. Diabetes 7 years prior to PET assessment was associated with a higher risk of a positive amyloid status [odds ratio (95% CI) = 3.68 (1.76; 7.61), P < 0.001] and higher standard uptake value ratios, indicating more severe Aβ pathology [standardized beta = 0.40 (0.17; 0.64), P = 0.001]. Hypertension was associated with higher SUVr values in APOE4 carriers (mean SUVr difference of 0.09), but not in non-carriers (mean SUVr difference 0.02; P = 0.005). In contrast, hypercholesterolaemia was related to lower SUVr values in APOE4 carriers (mean SUVr difference -0.06), but not in non-carriers (mean SUVr difference 0.02). Obesity, physical inactivity and smoking were not related to amyloid PET measures. The current findings suggest a contribution of diabetes, hypertension and hypercholesterolaemia to the pathophysiology of Alzheimer's disease in a general population of older non-demented adults. As these conditions respond well to lifestyle modification and drug treatment, further research should focus on the preventative effect of early risk management on the development of Alzheimer's disease neuropathology.

Valorizing the usage of olive leaves, bioactive compounds, biological activities, and food applications: A comprehensive review

Olive oil production is a significant source of economic profit for Mediterranean nations, accounting for around 98 percent of global output. Olive oil usage has increased dramatically in recent years, owing to its organoleptic characteristics and rising knowledge of its health advantages. The culture of olive trees and the manufacture of industrial and table olive oil produces enormous volumes of solid waste and dark liquid effluents, involving olive leaves, pomace, and olive oil mill wastewaters. These by-products cause an economic issue for manufacturers and pose major environmental concerns. As a result, partial reuse, like other agronomical production wastes, is a goal to be achieved. Because these by-products are high in bioactive chemicals, which, if isolated, might denote components with significant added value for the food, cosmetic, and nutraceutical sectors, indeed, they include significant amounts of beneficial organic acids, carbohydrates, proteins, fibers, and phenolic materials, which are distributed differently between the various wastes depending on the olive oil production method and table olive agronomical techniques. However, the extraction and recovery of bioactive materials from chosen by-products is a significant problem of their reasonable value, and rigorous detection and quantification are required. The primary aims of this review in this context are to outline the vital bioactive chemicals in olive by-products, evaluate the main developments in extraction, purification, and identification, and study their uses in food packaging systems and safety problems.

Plasma high-density lipoprotein cargo is altered in Alzheimer's disease and is associated with regional brain volume

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.

Cholesterol-induced robust Ca oscillation in astrocytes required for survival and lipid droplet formation in high-cholesterol condition

Cholesterol, one of the major cell membrane components, stabilizes membrane fluidity and regulates signal transduction. Beside its canonical roles, cholesterol has been reported to directly activate signaling pathways such as hedgehog (Hh). We recently found that astrocytes, one of the glial cells, respond to Hh pathway stimulation by Ca signaling. These notions led us to test if extracellularly applied cholesterol triggers Ca signaling in astrocytes. Here, we found that cholesterol application induces robust Ca oscillation only in astrocytes with different properties from the Hh-induced Ca response. The Ca oscillation has a long delay which corresponds to the onset of cholesterol accumulation in the plasma membrane. Blockade of the Ca oscillation resulted in enhancement of astrocytic cell death and disturbance of lipid droplet formation, implying a possibility that the cholesterol-induced Ca oscillation plays important roles in astrocytic survival and cholesterol handling under pathological conditions of cholesterol load such as demyelination.

•

Robust Ca oscillation by cholesterol in astrocytes but not in neurons and microglia

•

Cholesterol-induced Ca oscillation relates to membrane cholesterol accumulation

•

The Ca oscillation is driven via the PLC-IP₃ signaling pathway

•

Ca oscillation inhibition leads to astrocytic death and lipid droplet malformation

When the infectious environment meets the AD brain

Background

The Amyloid theory of Alzheimer’s disease (AD) suggests that the deposition of Amyloid β (Aβ) in the brain triggers a chain of events, involving the deposition of phosphorylated Tau and other misfolded proteins, leading to neurodegeneration via neuroinflammation, oxidative stress, and neurovascular factors. The infectious theory linked various infectious agents with the development of AD, raising the possibility that they serve as etiological causes of the disease. Are these theories mutually exclusive, or do they coincide?

Main body

In this review, we will discuss how the two theories converge. We present a model by which (1) the systemic infectious burden accelerates the development of AD brain pathology via bacterial Amyloids and other pathogen-associated molecular patterns (PAMPs), and (2) the developing AD brain pathology increases its susceptibility to the neurotoxicity of infectious agents -derived PAMPs, which drive neurodegeneration via activated microglia.

Conclusions

The reciprocal effects of amyloid deposition and systemic infectious burden may lead to a vicious cycle fueling Alzheimer’s disease pathogenesis.

Impact of A2T and D23N mutations on C99 homodimer conformations

The proteolytic cleavage of C99 by γ-secretase is the last step in the production of amyloid-β (Aβ) peptides. Previous studies have shown that membrane lipid composition, cholesterol concentration, and mutation in the transmembrane helix modified the structures and fluctuations of C99. In this study, we performed atomistic molecular dynamics simulations of the homodimer of the 55-residue congener of the C-terminal domain of the amyloid protein precursor, C99(1-55), in a POPC-cholesterol lipid bilayer, and we compared the conformational ensemble of WT sequence to those of the A2T and D23N variants. These mutations are particularly interesting as the protective Alzheimer's disease (AD) A2T mutation is known to decrease Aβ production, whereas the early onset AD D23N mutation does not affect Aβ production. We found noticeable differences in the structural ensembles of the three sequences. In particular, A2T varies from both WT and D23N by having long-range effects on the population of the extracellular justamembrane helix, the interface between the G29xxx-G33xxx-G37 motifs and the fluctuations of the transmembrane helical topologies.

Lipophilic Bioactive Compounds Transported in Triglyceride-Rich Lipoproteins Modulate Microglial Inflammatory Response

Microglial cells can contribute to Alzheimer’s disease by triggering an inflammatory response that leads to neuronal death. In addition, the presence of amyloid-β in the brain is consistent with alterations in the blood–brain barrier integrity and triglyceride-rich lipoproteins (TRL) permeation. In the present work, we used lab-made TRL as carriers of lipophilic bioactive compounds that are commonly present in dietary oils, namely oleanolic acid (OA), α-tocopherol (AT) and β-sitosterol (BS), to assess their ability to modulate the inflammatory response of microglial BV-2 cells. We show that treatment with lab-made TRL increases the release and gene-expression of IL-1β, IL-6, and TNF-α, as well as NO and iNOS in microglia. On the other hand, TRL revealed bioactive compounds α-tocopherol and β-sitosterol as suitable carriers for oleanolic acid. The inclusion of these biomolecules in TRL reduced the release of proinflammatory cytokines. The inclusion of these biomolecules in TRL reduced the release of proinflammatory cytokines. AT reduced IL-6 release by 72%, OA reduced TNF-α release by approximately 50%, and all three biomolecules together (M) reduced IL-1β release by 35% and TNF-α release by more than 70%. In addition, NO generation was reduced, with the inclusion of OA by 45%, BS by 80% and the presence of M by 88%. Finally, a recovery of the basal glutathione content was observed with the inclusion of OA and M in the TRL. Our results open the way to exploiting the neuro-pharmacological potential of these lipophilic bioactive compounds through their delivery to the brain as part of TRL.

Astrocytes and oligodendrocytes undergo subtype-specific transcriptional changes in Alzheimer's disease

Resolving glial contributions to Alzheimer's disease (AD) is necessary because changes in neuronal function, such as reduced synaptic density, altered electrophysiological properties, and degeneration, are not entirely cell autonomous. To improve understanding of transcriptomic heterogeneity in glia during AD, we used single-nuclei RNA sequencing (snRNA-seq) to characterize astrocytes and oligodendrocytes from apolipoprotein (APOE) Ɛ2/3 human AD and age- and genotype-matched non-symptomatic (NS) brains. We enriched astrocytes before sequencing and characterized pathology from the same location as the sequenced material. We characterized baseline heterogeneity in both astrocytes and oligodendrocytes and identified global and subtype-specific transcriptomic changes between AD and NS astrocytes and oligodendrocytes. We also took advantage of recent human and mouse spatial transcriptomics resources to localize heterogeneous astrocyte subtypes to specific regions in the healthy and inflamed brain. Finally, we integrated our data with published AD snRNA-seq datasets, highlighting the power of combining datasets to resolve previously unidentifiable astrocyte subpopulations.

Effects of Sex on the Relationship Between Apolipoprotein E Gene and Serum Lipid Profiles in Alzheimer’s Disease

Background

Sex is an important factor in studying the relationship between the APOE gene, lipid profiles, and AD. However, few studies have focused on the effect of sex on lipids in AD and normal controls with different APOE genes.

Materials and Methods

A total of 549 participants, including 298 AD patients and 251 body mass index (BMI)-matched healthy controls (HCs), were enrolled. Lipid profiles and APOE genes in both AD patients and HCs were determined.

Results

(1) TC and LDL were higher in AD patients than in HCs, only in APOEε4 carrying populations, but not in non-carrying populations. (2) TC and LDL were higher in APOEε4 allele carriers than in non-carriers, only in AD populations, but not in HCs. (3) The TC of APOEε2 carriers was lower than that of non-carriers in the male AD population, but not in the female AD population, female HCs, and male HCs. (4) The increased LDL level may increase the risk of AD in female people carrying APOEε4.

Conclusion

The TC and LDL levels of APOEε4 carriers were higher than those of non-carriers, and the effect was more significant in the female AD population. The TC levels in APOEε2 carriers were lower than those in non-carriers, which was more significant in the male AD population.

Guanabenz mitigates the neuropathological alterations and cell death in Alzheimer's disease

Alzheimer's disease (AD) pathology is characterized by cognitive impairment, increased acetylcholinesterase (AChE) activity, and impaired neuronal communication. Clinically, AChE inhibitors are being used to treat AD patients; however, these remain unable to prevent the disease progression. Therefore, further development of new therapeutic molecules is required having broad spectrum effects on AD-related various neurodegenerative events. Since repurposing is a quick mode to search the therapeutic molecules; henceforth, this study was conducted to evaluate the anti-Alzheimer activity of drug guanabenz which is already in use for the management of high blood pressure in clinics. The study was performed employing both cellular and rat models of AD along with donepezil as reference drug. Guanabenz treatment in both the experimental models showed significant protection against AD-specific behavioral and pathological indicators like AChE activity, tau phosphorylation, amyloid precursor protein, and memory retention. In conjunction, guanabenz also attenuated the AD-related oxidative stress, impaired mitochondrial functionality (MMP, cytochrome-c translocation, ATP level, and mitochondrial complex I activity), endoplasmic reticulum stress (GRP78, GADD153, cleaved caspase-12), neuronal apoptosis (Bcl-2, Bax, cleaved caspase-3), and DNA fragmentation. In conclusion, findings suggested the panoptic protective effect of guanabenz on disease-related multiple degenerative markers and signaling. Furthermore, clinical trial may shed light and expedite the availability of new therapeutic anti-Alzheimer's molecule for the wellbeing of AD patients.

Connecting the Dots Between Hypercholesterolemia and Alzheimer’s Disease: A Potential Mechanism Based on 27-Hydroxycholesterol

Alzheimer’s disease (AD), the most common cause of dementia, is a complex and multifactorial disease involving genetic and environmental factors, with hypercholesterolemia considered as one of the risk factors. Numerous epidemiological studies have reported a positive association between AD and serum cholesterol levels, and experimental studies also provide evidence that elevated cholesterol levels accelerate AD pathology. However, the underlying mechanism of hypercholesterolemia accelerating AD pathogenesis is not clear. Here, we review the metabolism of cholesterol in the brain and focus on the role of oxysterols, aiming to reveal the link between hypercholesterolemia and AD. 27-hydroxycholesterol (27-OHC) is the major peripheral oxysterol that flows into the brain, and it affects β-amyloid (Aβ) production and elimination as well as influencing other pathogenic mechanisms of AD. Although the potential link between hypercholesterolemia and AD is well established, cholesterol-lowering drugs show mixed results in improving cognitive function. Nevertheless, drugs that target cholesterol exocytosis and conversion show benefits in improving AD pathology. Herbs and natural compounds with cholesterol-lowering properties also have a potential role in ameliorating cognition. Collectively, hypercholesterolemia is a causative risk factor for AD, and 27-OHC is likely a potential mechanism for hypercholesterolemia to promote AD pathology. Drugs that regulate cholesterol metabolism are probably beneficial for AD, but more research is needed to unravel the mechanisms involved in 27-OHC, which may lead to new therapeutic strategies for AD.

Hypothyroidism and Diabetes-Related Dementia: Focused on Neuronal Dysfunction, Insulin Resistance, and Dyslipidemia

The incidence of dementia is steadily increasing worldwide. The risk factors for dementia are diverse, and include genetic background, environmental factors, sex differences, and vascular abnormalities. Among the subtypes of dementia, diabetes-related dementia is emerging as a complex type of dementia related to metabolic imbalance, due to the increase in the number of patients with metabolic syndrome and dementia worldwide. Thyroid hormones are considered metabolic regulatory hormones and affect various diseases, such as liver failure, obesity, and dementia. Thyroid dysregulation affects various cellular mechanisms and is linked to multiple disease pathologies. In particular, hypothyroidism is considered a critical cause for various neurological problems-such as metabolic disease, depressive symptoms, and dementia-in the central nervous system. Recent studies have demonstrated the relationship between hypothyroidism and brain insulin resistance and dyslipidemia, leading to diabetes-related dementia. Therefore, we reviewed the relationship between hypothyroidism and diabetes-related dementia, with a focus on major features of diabetes-related dementia such as insulin resistance, neuronal dysfunction, and dyslipidemia.

Lipid levels and the risk of dementia: A dose-response meta-analysis of prospective cohort studies

OBJECTIVES

We performed a dose-response meta-analysis to estimate the association between lipid profiles with the risk of dementia and the potential differences according to the subtype of dementia based on prospective studies.

METHODS

We searched PubMed, Embase and Web of Science for relevant articles and performed a meta-analysis. We applied fixed or random-effects models to calculate pooled relative risk (RR) with their 95% confidence intervals (CI). The dose-response relationship was assessed by restricted cubic spline.

RESULTS

Twenty-five prospective studies comprising 362,443 participants and 20,121 cases were included in the final analysis. We found that increased risk of all-cause dementia could be predicted by elevated total cholesterol (TC) (RR = 1.13, 95% CI 1.04-1.22). When looking at dementia subtypes, we also observed high TC and triglycerides (TG) may increase the future risk of Alzheimer's disease (AD), with a pooled RR of 1.13 (95% CI: 1.06-1.21) and 1.10 (95% CI: 1.04-1.15) respectively. Moreover, a dose-response analysis revealed a linear association between TC or TG and the risk of AD, with a pooled RR of 1.09 (95% CI: 1.02-1.16) and 1.12 (95% CI: 1.05-1.21) for per 3-mmol/L increment in TC and TG, respectively.

CONCLUSIONS

Current evidence suggest that every 3-mmol/L increase in blood TC or TG is linearly associated with a 9% or 12% increase in RR of AD, supporting the notion that high TC and TG levels appear to play a causal role in the development of AD.

Palmitic Acid and Oleic Acid Differently Modulate TLR2-Mediated Inflammatory Responses in Microglia and Macrophages

The relationship between systemic immunity and neuroinflammation is widely recognised. Infiltration of peripheral immune cells to the CNS during certain chronic inflammatory states contributes significantly to neuropathology. Obesity and its co-morbidities are primary risk factors for neuroinflammatory and neurodegenerative conditions, including Alzheimer’s disease (AD). Dietary fats are among the most proinflammatory components of the obesogenic diet and play a prominent role in the low-grade systemic inflammation associated with the obese state. Saturated fatty acid (SFA) is largely implicated in the negative consequences of obesity, while the health benefits of monounsaturated fatty acid (MUFA) are widely acknowledged. The current study sought to explore whether SFA and MUFA differently modulate inflammatory responses in the brain, compared with peripheral immune cells. Moreover, we assessed the neuroinflammatory impact of high-fat-induced obesity and hypothesised that a MUFA-rich diet might mitigate inflammation despite obesogenic conditions. Toll-like receptor (TLR)2 mediates the inflammation associated with both obesity and AD. Using the TLR2 agonist lipoteichoic acid (LTA), we report that pre-exposure to either palmitic acid (PA) or oleic acid (OA) attenuated cytokine secretion from microglia, but heightened sensitivity to nitric oxide (NO) production. The reduction in cytokine secretion was mirrored in LTA-stimulated macrophages following exposure to PA only, while effects on NO were restricted to OA, highlighting important cell-specific differences. An obesogenic diet over 12 weeks did not induce prominent inflammatory changes in either cortex or hippocampus, irrespective of fat composition. However, we reveal a clear disparity in the effects of MUFA under obesogenic and non-obesogenic conditions.

Mechanistic Link between Vitamin B12 and Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly population, affecting over 55 million people worldwide. Histopathological hallmarks of this multifactorial disease are an increased plaque burden and tangles in the brains of affected individuals. Several lines of evidence indicate that B12 hypovitaminosis is linked to AD. In this review, the biochemical pathways involved in AD that are affected by vitamin B12, focusing on APP processing, Aβ fibrillization, Aβ-induced oxidative damage as well as tau hyperphosphorylation and tau aggregation, are summarized. Besides the mechanistic link, an overview of clinical studies utilizing vitamin B supplementation are given, and a potential link between diseases and medication resulting in a reduced vitamin B12 level and AD are discussed. Besides the disease-mediated B12 hypovitaminosis, the reduction in vitamin B12 levels caused by an increasing change in dietary preferences has been gaining in relevance. In particular, vegetarian and vegan diets are associated with vitamin B12 deficiency, and therefore might have potential implications for AD. In conclusion, our review emphasizes the important role of vitamin B12 in AD, which is particularly important, as even in industrialized countries a large proportion of the population might not be sufficiently supplied with vitamin B12.

Association Between Gout and Dementia in the Elderly: A Nationwide Population-Based Cohort Study

OBJECTIVE

The data showing the association between gout and dementia are inconsistent. The objective of this study was to examine whether gout is associated with the risk of dementia in the elderly.

METHODS

This retrospective cohort study used population-based representative claims data from the National Health Insurance Service in Korea. We used the Elderly Cohort database which represents 10% of the elderly Koreans over the age of 60, from 2002 to 2013. We assessed the association of gout with a new diagnosis of dementia with Cox proportional hazard models and adjusted the data for potential covariates such as demographics (age, sex) and comorbidities.

RESULTS

We included 22,178 patients with gout and 113,590 without. In each group, 2,557 (11.53%) and 18,264 (16.08%) patients, respectively, had dementia. In multivariable analyses, gout was independently associated with a significantly lower hazard ratio of incident dementia, with an adjusted hazard ratio of 0.63 (95% CI, 0.60-0.66). A sub-group analysis conducted to find out the effects of gout medication showed that febuxostat use significantly decreased incident dementia.

CONCLUSION

Gout was independently associated with a 37% lower risk of dementia in the elderly.

An evidence-based review of neuronal cholesterol role in dementia and statins as a pharmacotherapy in reducing risk of dementia

INTRODUCTION

Dementia is a progressive neurodegenerative disorder impairing memory and cognition. Alzheimer's Disease, followed by vascular dementia - the most typical form. Risk factors for vascular dementia include diabetes, cardiovascular disease, hyperlipidemia. Lipids' levels are significantly associated with vascular changes in the brain.

AREAS COVERED

The present article reviews the cholesterol metabolism in the brain, which includes: the synthesis, transport, storage, and elimination process. Additionally, it reviews the role of cholesterol in the pathogenesis of dementia and statin as a therapeutic intervention in dementia. In addition to the above, it further reviews evidence in support of as well as against statin therapy in dementia, recent updates of statin pharmacology, and demerits of use of statin pharmacotherapy.

EXPERT OPINION

Amyloid-β peptides and intraneuronal neurofibrillary tangles are markers of Alzheimer's disease. Evidence shows cholesterol modulates the functioning of enzymes associated with Amyloid-β peptide processing and synthesis. Lowering cholesterol using statin may help prevent or delay the progression of dementia. This paper reviews the role of statin in dementia and recommends extensive future studies, including genetic research, to obtain a precise medication approach for patients with dementia.

Neurodegenerative Diseases and Cholesterol: Seeing the Field Through the Players

Neurodegenerative diseases, namely Alzheimer’s (AD), Parkinson’s (PD), and Huntington’s disease (HD) together with amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS), devastate millions of lives per year worldwide and impose an increasing socio-economic burden across nations. Consequently, these diseases occupy a considerable portion of biomedical research aiming to understand mechanisms of neurodegeneration and to develop efficient treatments. A potential culprit is cholesterol serving as an essential component of cellular membranes, as a cofactor of signaling pathways, and as a precursor for oxysterols and hormones. This article uncovers the workforce studying research on neurodegeneration and cholesterol using the TeamTree analysis. This new bibliometric approach reveals the history and dynamics of the teams and exposes key players based on citation-independent metrics. The team-centered view reveals the players on an important field of biomedical research.

Axonal plasma membrane-mediated toxicity of cholesterol in Alzheimer's disease: A microsecond molecular dynamics study

Alzheimer's disease is increasingly being recognized as an immune-mediated disease of brain. Since physiological brain health and brain immune function is dependent upon homeostatic neuronal membrane structure and function, alterations in membrane lipid biochemistry may predispose to disease. Brain is rich in cholesterol, and cholesterol metabolism dysfunction is a known risk factor for AD. Employing extensive microsecond all-atom molecular dynamics simulations, we investigated the properties of model neuronal membranes as a function of cholesterol concentration; phospholipid and phospholipid/cholesterol bilayers were also simulated to compare against available experimental data. Increased cholesterol concentrations compact and stiffen the lipid membrane, reducing permeability while modulating local water densities in the peri-membranous environment. Conversely, lower cholesterol mole fraction yields membranes with increased molecular disorder, enhanced fluidity, higher molecular tilting, and augmented interdigitation between bilayer leaflet lipids. Our findings provide a molecular insight on effect of cholesterol composition on various biochemical processes occurring at neuronal axon plasma membrane. These calculations also endeavor to establish a membrane-based link between cholesterol as an AD risk factor and possible AD pathology.

Methyl-Beta-Cyclodextrin Restores KIR Channel Function in Brain Endothelium of Female Alzheimer's Disease Mice

Background:

As the sixth-leading cause of death in the United States, Alzheimer’s disease (AD) entails deteriorating endothelial control of blood flow throughout the brain. In particular, reduced inward-rectifying K⁺ (K_IR) channel function in animal models of aging and AD compromises endothelial function and optimal perfusion of brain parenchyma. Deficient endothelial K_IR channels may result from aberrant interaction with plasma membrane cholesterol as a primary regulator of membrane fluidity and ion channels.

Objective:

We tested the hypothesis that mild methyl-β-cyclodextrin (MβCD) treatment to reduce membrane cholesterol may restore endothelial K_IR channel function in brain endothelium of old AD mice.

Methods:

Membrane potential was continuously measured in isolated endothelial tubes from posterior cerebral arteries of young (1 to 3 months) and old (16 to 19 months) female 3xTg-AD mice before and after mild treatment with the cholesterol-removing agent MβCD (1 mmol/L). Elevated extracellular potassium ([K⁺]_E; 15 mmol/L) and NS309 (1μmol/L) activated K_IR and Ca²⁺-activated K⁺ (SK_Ca/IK_Ca) channels respectively before and after MβCD treatment.

Results:

SK_Ca/IK_Ca channel function for producing hyperpolarization remained stable regardless of age group and MβCD treatment (ΔV_m: ∼–33 mV). However, as deficient during AD, K_IR channel function was restored (ΔV_m: –9±1 mV) versus pre-MβCD conditions (–5±1 mV); a progressive effect that reached –14±1 mV hyperpolarization at 60 min following MβCD washout.

Conclusion:

In female animals, MβCD treatment of brain endothelium selectively restores K_IR versus SK_Ca/IK_Ca channel function during AD. Thus, the endothelial cholesterol-K_IR channel interface is a novel target for ameliorating perfusion of the AD brain.

Blood Triglyceride and High-Density Lipoprotein Levels Are Associated with Plasma Amyloid-β Transport: A Population-Based Cross-Sectional Study

BACKGROUND

Studies have found that blood lipids are associated with plasma amyloid-β (Aβ) levels, but the underlying mechanism is still unclear. Two Aβ transporters, soluble form of low-density lipoprotein receptor related protein-1 (sLRP1) and soluble receptor of advanced glycation end products (sRAGE), are crucial in peripheral Aβ transport.

OBJECTIVE

The aim was to investigate the effects of lipids on the relationships between plasma Aβ and transporter levels.

METHODS

This study included 1,436 adults aged 40 to 88 years old. Blood Aβ, sLRP1, sRAGE, and lipid levels were measured. Univariate and multivariate analyses were used to analyze the relationships between lipids and plasma Aβ, sLRP1, and sRAGE.

RESULTS

After adjusting for all possible covariates, high-density lipoprotein (HDL-c) was positively associated with plasma Aβ42 and sRAGE (β= 6.158, p = 0.049; β= 121.156, p < 0.001, respectively), while triglyceride (TG) was negatively associated with plasma Aβ40, Aβ42, and sRAGE (β= -48.389, p = 0.017; β= -11.142, p = 0.020; β= -147.937, p = 0.003, respectively). Additionally, positive correlations were found between plasma Aβ and sRAGE in the normal TG (Aβ40: β= 0.034, p = 0.005; Aβ42: β= 0.010, p = 0.001) and HDL-c groups (Aβ40: β= 0.023, p = 0.033; Aβ42: β= 0.008, p = 0.002) but not in the high TG and low HDL-c groups.

CONCLUSION

Abnormal levels of TG and HDL-c are associated with decreased Aβ and sRAGE levels. Positive correlations between plasma Aβ and sRAGE were only found in the normal TG and HDL-c groups but not in the high TG and low HDL-c groups. These results indicated that dyslipidemia contributing to plasma Aβ levels might also be involved in peripheral Aβ clearance.

Plasma High Density Lipoprotein Small Subclass is Reduced in Alzheimer's Disease Patients and Correlates with Cognitive Performance

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 Aβ_1–42 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.

Impact of age, hypercholesterolemia, and the vitamin D receptor on brain endogenous β-amyloid peptide accumulation in mice

Age, hypercholesterolemia, and vitamin D deficiency are risk factors that increase the brain accumulation of pathogenic β-amyloid peptides (40 and 42), precursors leading to Alzheimer's disease (AD) in humans. The relative changes accompanying aging, high cholesterol, and/or treatment of calcitriol, active vitamin D receptor (VDR) ligand, under normal physiology are unknown. We examined these relative changes in C57BL/6 mice of ages 2, 4-8, and more than 10 months old, which were fed a normal or high fat / high cholesterol diet and treated with calcitriol, active ligand of the vitamin D receptor (0 or 2.5 μg/kg ×4, intraperitoneally, every other day to elicit cholesterol lowering in liver). Aβ₄₀ but not Aβ₄₂ accumulation in brain and lower P-glycoprotein (P-gp) and neprilysin protein expressions for Aβ efflux and degradation, respectively, were found to be associated with aging. But there was no trend for BACE1 (β-secretase 1, a cholesterol-sensitive enzyme) toward Aβ synthesis with age. In response to calcitriol treatment, P-gp was elevated, mitigating partially the age-related changes. Although age-dependent decreasing trends in mRNA expression levels existed for Cyp46a1, the brain cholesterol processing enzyme, whose inhibition increases BACE1 and ApoE to facilitate microglia Aβ degradation, mRNA changes for other cholesterol transporters: Acat1 and Abca1, and brain cholesterol levels remained unchanged. There was no observable change in the mRNA expression of amyloid precursor protein (APP) and the influx (RAGE) and efflux (LRP1) transporters with respect to age, diet, or calcitriol treatment. Overall, aging poses as a risk factor contributing to Aβ accumulation in brain, and VDR-mediated P-gp activation partially alleviates the outcome.

A High Fat/Cholesterol Diet Recapitulates Some Alzheimer's Disease-Like Features in Mice: Focus on Hippocampal Mitochondrial Dysfunction

BACKGROUND

Ample evidence from clinical and pre-clinical studies suggests mid-life hypercholesterolemia as a risk factor for developing Alzheimer's disease (AD) at a later age. Hypercholesterolemia induced by dietary habits can lead to vascular perturbations that increase the risk of developing sporadic AD.

OBJECTIVE

To investigate the effects of a high fat/cholesterol diet (HFCD) as a risk factor for AD by using a rodent model of AD and its correspondent control (healthy animals).

METHODS

We compared the effect of a HFCD in normal mice (non-transgenic mice, NTg) and the triple transgenic mouse model of AD (3xTgAD). We evaluated cognitive performance in relation to changes in oxidative metabolism and neuron-derived nitric oxide (•NO) concentration dynamics in hippocampal slices as well as histochemical staining of markers of the neurovascular unit.

RESULTS

In NTg, the HFCD produced only moderate hypercholesterolemia but significant decline in spatial memory was observed. A tendency for decrease in •NO production was accompanied by compromised mitochondrial function with decrease in spare respiratory capacity. In 3xTgAD mice, a robust increase in plasma cholesterol levels with the HFCD did not worsen cognitive performance but did induce compromise of mitochondrial function and significantly decreased •NO production. We found increased staining of biomarkers for astrocyte endfeet and endothelial cells in 3xTgAD hippocampi, which was further increased by the HFCD.

CONCLUSION

A short term (8 weeks) intervention with HFCD can produce an AD-like phenotype even in the absence of overt systemic hypercholesterolemia and highlights mitochondrial dysfunction as a link between hypercholesterolemia and sporadic AD.

Fatty acids and beyond: Age and Alzheimer's disease related changes in lipids reveal the neuro-nutraceutical potential of lipids in cognition

Lipids are essential in maintaining brain function, and lipid profiles have been reported to be altered in aged and Alzheimer's disease (AD) brains as compared to healthy mature brains. Both age and AD share common metabolic hallmarks such as increased oxidative stress and perturbed metabolic function, and age remains the most strongly correlated risk factor for AD, a neurodegenerative disease. A major accompanying pathological symptom of these conditions is cognitive impairment, which is linked with changes in lipid metabolism. Thus, nutraceuticals that affect brain lipid metabolism or lipid levels as a whole have the potential to ameliorate cognitive decline. Lipid analyses and lipidomic studies reveal changes in specific lipid types with aging and AD, which can identify potential lipid-based nutraceuticals to restore the brain to a healthy lipid phenotype. The brain lipid profile can be influenced directly with dietary administration of lipids themselves, although because of synergistic effects of nutrients it may be more useful to consider a multi-component diet rather than single nutrient supplementation. Gut microbiota also serve as a source of beneficial lipids, and the value of treatments that manipulate the composition of gut microbiome should not be ignored. Lastly, instead of direct supplementation, compounds that affect pathways involved with lipid metabolism should also be considered as a way of manipulating lipid levels to improve cognition. In this review, we briefly discuss the role of lipids in the brain, the changing lipid profile in AD, current research on lipid-based nutraceuticals and their therapeutic potential to combat cognitive impairment.

Cholesterol and Alzheimer's Disease; From Risk Genes to Pathological Effects

While the central nervous system compromises 2% of our body weight, it harbors up to 25% of the body's cholesterol. Cholesterol levels in the brain are tightly regulated for physiological brain function, but mounting evidence indicates that excessive cholesterol accumulates in Alzheimer's disease (AD), where it may drive AD-associated pathological changes. This seems especially relevant for late-onset AD, as several of the major genetic risk factors are functionally associated with cholesterol metabolism. In this review we discuss the different systems that maintain brain cholesterol metabolism in the healthy brain, and how dysregulation of these processes can lead, or contribute to, Alzheimer's disease. We will also discuss how AD-risk genes might impact cholesterol metabolism and downstream AD pathology. Finally, we will address the major outstanding questions in the field and how recent technical advances in CRISPR/Cas9-gene editing and induced pluripotent stem cell (iPSC)-technology can aid to study these problems.