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.

A Mendelian randomization study of the entire phenome to explore the causal links between epilepsy

OBJECTIVE

The causes and triggering factors of epilepsy are still unknown. The results of genome-wide association studies can be utilized for a phenome-wide association study using Mendelian randomization (MR) to identify potential risk factors for epilepsy.

METHODS

This study utilizes two-sample MR analysis to investigate whether 316 phenotypes, including lifestyle, environmental factors, blood biomarker, and more, are causally associated with the occurrence of epilepsy. The primary analysis employed the inverse variance weighted (IVW) model, while complementary MR analysis methods (MR Egger, Wald ratio) were also employed. Sensitivity analyses were also conducted to evaluate heterogeneity and pleiotropy.

RESULTS

There was no evidence of a statistically significant causal association between the examined phenotypes and epilepsy following Bonferroni correction (p < 1.58 × 10-4) or false discovery rate correction. The results of the MR analysis indicate that the frequency of tiredness or lethargy in the last 2 weeks (p = 0.042), blood uridine (p = 0.003), blood propionylcarnitine (p = 0.041), and free cholesterol (p = 0.044) are suggestive causal risks for epilepsy. Lifestyle choices, such as sleep duration and alcohol consumption, as well as biomarkers including steroid hormone levels, hippocampal volume, and amygdala volume were not identified as causal factors for developing epilepsy (p > 0.05).

CONCLUSIONS

Our study provides additional insights into the underlying causes of epilepsy, which will serve as evidence for the prevention and control of epilepsy. The associations observed in epidemiological studies may be partially attributed to shared biological factors or lifestyle confounders.

Association between Age at Diagnosis of Hyperlipidemia and Subsequent Risk of Dementia

OBJECTIVES

The relationship between age at diagnosis of hyperlipidemia and dementia remains unclear. We examined whether younger age at diagnosis of hyperlipidemia is associated with higher risk of subsequent dementia.

DESIGN

A longitudinal population-based study with a median follow-up of 12.8 years.

SETTING AND PARTICIPANTS

We analyzed data on a sample of 489,642 participants in the United Kingdom.

METHODS

This study was based on the UK Biobank. Information on hyperlipidemia and dementia diagnoses was collected at baseline (2006-2010) and follow-up [median = 12.8 years, interquartile range (IQR): 12.1-13.6 years]. Propensity score matching method and Cox proportional hazards models were used to assess the association between age at diagnosis of hyperlipidemia and dementia.

RESULTS

Among 489,642 participants (mean age: 56.9 ± 8.1 years; female: 54.7%), 114,112 (23.3%) were diagnosed with hyperlipidemia. Younger age at diagnosis of hyperlipidemia (per 10-year decrease) was significantly associated with higher risks of all-cause dementia [hazard ratio (HR), 1.12; 95% CI, 1.07-1.18; P < .001], Alzheimer's disease (AD) (HR, 1.22; 95% CI, 1.14-1.31; P < .001), and vascular dementia (VD) (HR, 1.16; 95% CI, 1.05-1.27; P < .001). After propensity score matching, patients with hyperlipidemia diagnosed before 50 years had the highest HR for all-cause dementia (HR, 1.46; 95% CI, 1.15-1.86; P = .002), followed by patients diagnosed between 50 and 69 years (HR, 1.21; 95% CI, 1.12-1.31; P < .001) and then patients diagnosed aged 70 years and older (HR, 0.94; 95% CI, 0.84-1.06; P = .302). Similar results were observed for AD and VD.

CONCLUSIONS AND IMPLICATIONS

A dose-response relationship between age at hyperlipidemia diagnosis and risk of dementia was found in the longitudinal cohort study, with younger age at diagnosis of hyperlipidemia being associated with higher subsequent risk.

Oxysterols as Biomarkers of Aging and Disease

Oxysterols derive from either enzymatic or non-enzymatic oxidation of cholesterol. Even though they are produced as intermediates of bile acid synthesis pathway, they are recognised as bioactive compounds in cellular processes. Therefore, their absence or accumulation have been shown to be associated with disease phenotypes. This chapter discusses the contribution of oxysterol to ageing, age-related diseases such as neurodegeneration and various disorders such as cancer, cardiovascular disease, diabetes, metabolic and ocular disorders. It is clear that oxysterols play a significant role in development and progression of these diseases. As a result, oxysterols are being investigated as suitable markers for disease diagnosis purposes and some drug targets are in development targeting oxysterol pathways. However, further research will be needed to confirm the suitability of these potentials.

Implication of Oxysterols and Phytosterols in Aging and Human Diseases

Cholesterol is easily oxidized and can be transformed into numerous oxidation products, among which oxysterols. Phytosterols are plant sterols related to cholesterol. Both oxysterols and phytosterols can have an impact on human health and diseases.Cholesterol is a member of the sterol family that plays essential roles in biological processes, including cell membrane stability and myelin formation. Cholesterol can be metabolized into several molecules including bile acids, hormones, and oxysterols. On the other hand, phytosterols are plant-derived compounds structurally related to cholesterol, which can also have an impact on human health. Here, we review the current knowledge about the role of oxysterols and phytosterols on human health and focus on the impact of their pathways on diseases of the central nervous system (CNS), autoimmune diseases, including inflammatory bowel diseases (IBD), vascular diseases, and cancer in both experimental models and human studies. We will first discuss the implications of oxysterols and then of phytosterols in different human diseases.

Effect and Mechanism of Rapamycin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Alzheimer's disease (AD), the most common form of dementia, remains long-term and challenging to diagnose. Furthermore, there is currently no medication to completely cure AD patients. Rapamycin has been clinically demonstrated to postpone the aging process in mice and improve learning and memory abilities in animal models of AD. Therefore, rapamycin has the potential to be significant in the discovery and development of drugs for AD patients.

Objective

The main objective of this systematic review and meta-analysis was to investigate the effects and mechanisms of rapamycin on animal models of AD by examining behavioral indicators and pathological features.

Methods

Six databases were searched and 4,277 articles were retrieved. In conclusion, 13 studies were included according to predefined criteria. Three authors independently judged the selected literature and methodological quality. Use of subgroup analyses to explore potential mechanistic effects of rapamycin interventions: animal models of AD, specific types of transgenic animal models, dosage, and periodicity of administration.

Results

The results of Morris Water Maze (MWM) behavioral test showed that escape latency was shortened by 15.60 seconds with rapamycin therapy, indicating that learning ability was enhanced in AD mice; and the number of traversed platforms was increased by 1.53 times, indicating that the improved memory ability significantly corrected the memory deficits.

CONCLUSIONS

Rapamycin therapy reduced age-related plaque deposition by decreasing AβPP production and down-regulating β-secretase and γ-secretase activities, furthermore increased amyloid-β clearance by promoting autophagy, as well as reduced tau hyperphosphorylation by up-regulating insulin-degrading enzyme levels.

Mechanisms of 3-Hydroxyl 3-Methylglutaryl CoA Reductase in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide and has a high incidence in the elderly. Unfortunately, there is no effective therapy for AD owing to its complicated pathogenesis. However, the development of lipid-lowering anti-inflammatory drugs has heralded a new era in the treatment of Alzheimer's disease. Several studies in recent years have shown that lipid metabolic dysregulation and neuroinflammation are associated with the pathogenesis of AD. 3-Hydroxyl 3-methylglutaryl CoA reductase (HMGCR) is a rate-limiting enzyme in cholesterol synthesis that plays a key role in cholesterol metabolism. HMGCR inhibitors, known as statins, have changed from being solely lipid-lowering agents to neuroprotective compounds because of their effects on lipid levels and inflammation. In this review, we first summarize the main regulatory mechanism of HMGCR affecting cholesterol biosynthesis. We also discuss the pathogenesis of AD induced by HMGCR, including disordered lipid metabolism, oxidative stress, inflammation, microglial proliferation, and amyloid-β (Aβ) deposition. Subsequently, we explain the possibility of HMGCR as a potential target for AD treatment. Statins-based AD treatment is an ascent field and currently quite controversial; therefore, we also elaborate on the current application prospects and limitations of statins in AD treatment.

Reexamining the Causes and Effects of Cholesterol Deposition in the Brains of Patients with Alzheimer's Disease

Alzheimer's disease (AD) is a degenerative disease of the central nervous system. Numerous studies have shown that imbalances in cholesterol homeostasis in the brains of AD patients precede the onset of clinical symptoms. In addition, cholesterol deposition has been observed in the brains of AD patients even though peripheral cholesterol does not enter the brain through the blood‒brain barrier (BBB). Studies have demonstrated that cholesterol metabolism in the brain is associated with many pathological conditions, such as amyloid beta (Aβ) production, Tau protein phosphorylation, oxidative stress, and inflammation. In 2022, some scholars put forward a new hypothesis of AD: the disease involves lipid invasion and its exacerbation of the abnormal metabolism of cholesterol in the brain. In this review, by discussing the latest research progress, the causes and effects of cholesterol retention in the brains of AD patients are analyzed and discussed. Additionally, the possible mechanism through which AD may be improved by targeting cholesterol is described. Finally, we propose that improving the impairments in cholesterol removal observed in the brains of AD patients, instead of further reducing the already impaired cholesterol synthesis in the brain, may be the key to preventing cholesterol deposition and improving the corresponding pathological symptoms.

Causal associations between blood lipids and brain structures: a Mendelian randomization study

The potential causal association between dyslipidemia and brain structures remains unclear. Therefore, this study aimed to investigate whether circulating lipids are causally associated with brain structure alterations using Mendelian randomization analysis. Genome-wide association study summary statistics of blood lipids and brain structures were obtained from publicly available databases. Inverse-variance weighted method was used as the primary method to assess causality. In addition, four additional Mendelian randomization methods (MR-Egger, weighted median, simple mode, and weighted mode) were applied to supplement inverse-variance weighted. Furthermore, Cochrane's Q test, MR-Egger intercept test, MR-PRESSO global test, and leave-one-out analysis were performed for sensitivity analyses. After Bonferroni corrections, two causal associations were finally identified: elevated non-high-density lipoprotein cholesterol level leads to higher average cortical thickness (β = 0.0066 mm, 95% confidence interval: 0.0045-0.0087 mm, P = 0.001); and elevated high-density lipoprotein cholesterol level leads to higher inferior temporal surface area (β = 18.6077 mm2, 95% confidence interval: 11.9835-25.2320 mm2, P = 0.005). Four additional Mendelian randomization methods indicated parallel results. Sensitivity tests demonstrated the stability. Overall, the present study showed causal relationships between several lipid profiles and specific brain structures, providing new insights into the link between dyslipidemia and neurological disorders.

Ferulic acid alleviates high fat diet-induced cognitive impairment by inhibiting oxidative stress and apoptosis

Cognitive impairment has become a major public health problem. Growing evidence suggests that high-fat diet (HFD) can cause cognitive dysfunction and increase the risk of dementia. However, effective treatment for cognitive impairment is not available. Ferulic acid (FA) is a single phenolic compound with anti-inflammatory and antioxidant properties. Nevertheless, its role in regulating learning and memory in HFD-fed mice and the underlying mechanism remains unclear. In this study, we aimed to identify the neuroprotective mechanisms of FA in HFD induced cognitive impairment. We found that FA improved the survival rate of HT22 cells treated with palmitic acid (PA), inhibited cell apoptosis, and reduced oxidative stress via the IRS1/PI3K/AKT/GSK3β signaling pathway; Furthermore, FA treatment for 24 weeks improved the learning and memory of HFD-fed mice and decreased hyperlipidemia. Moreover, the expression of Nrf2 and Gpx4 proteins were decreased in HFD-fed mice. After FA treatment, the decline of these proteins was reversed. Our study showed that the neuroprotective effect of FA on cognitive impairment was related to the inhibition of oxidative stress and apoptosis and regulation of glucose and lipid metabolism. These findings suggested that FA can be developed as a potential agent for the treatment of HFD-induced cognitive impairment.

QEEG indices are associated with inflammatory and metabolic risk factors in Parkinson's disease dementia: An observational study

BACKGROUND

Quantitative electroencephalography (QEEG) is a reliable and non-invasive diagnostic tool to quantify cortical synaptic injury or loss in the clinical assessment of neurodegenerative diseases, and may be able to differentiate various types of dementia. We investigated if QEEG indices can differentiate Parkinson's Disease (PD) with nondementia (PD-ND) from PD with dementia (PDD), and to determine if QEEG indices correlate with inflammation and lipid metabolism markers in PD.

METHODS

This clinical study collected data between July 1, 2018 and July 1, 2021 in Zhujiang Hospital of Southern Medical University in China and data was analysed. A total of 125 individuals comprising of 31 PDD, 47 patients with PD-ND and 47 healthy controls were included. We calculated the absolute spectral power (ASP) of frequency bands and the slow-to-fast frequency ratios of specific brain regions. Plasma levels of hypersensitive C-reactive protein (Hs-CRP), superoxide dismutase (SOD), and high-density lipoprotein cholesterol (HDL-C) were measured and correlations with QEEG indices were examined.

FINDINGS

A significantly higher ASP of delta frequency especially in the frontal region was observed in patients with PDD compared to PD-ND (P=0.004) and controls (P=0.000). Decreased HDL-C (OR=0.186, P=0.030), and increased Hs-CRP (OR =2.856, P=0.015) were associated with PDD. Frontal-delta ASP was negatively correlated with plasma HDL-C (r=-0.353, P=0.000) and SOD (r=-0.322, P=0.001), and positively correlated with Hs-CRP (r=0.342, P=0.000).

INTERPRETATION

We highlight novel correlations between QEEG indices and inflammation and lipid metabolism markers in PD-ND and PDD. QEEG indices, HDL-C and Hs-CRP are potentially useful for the evaluation of PDD. Our current findings suggest that peripheral inflammation might contribute to the pathogenesis of cognitive impairment and EEG slowing in PDD. The mechanism underlying frontal-delta ASP and its correlation with neuro-inflammatory and metabolic markers in PDD should be further investigated.

FUNDING

The National Natural Science Foundation of China (NO: 81873777, 82071414); the Scientific Research Foundation of Guangzhou (NO: 202206010005); the Science and Technology Program of Guangdong of China (NO: 2020A0505100037); the High-level Hospital Construction Research Project of Maoming People's Hospital (NO: xz2020009); the Science and Technology Program of Maoming City (NO: 2021S0026). Dr EK Tan is supported by the National Medical Research Council, Singapore.

Remodeling of the Neurovascular Unit Following Cerebral Ischemia and Hemorrhage

Formulated as a group effort of the stroke community, the transforming concept of the neurovascular unit (NVU) depicts the structural and functional relationship between brain cells and the vascular structure. Composed of both neural and vascular elements, the NVU forms the blood-brain barrier that regulates cerebral blood flow to meet the oxygen demand of the brain in normal physiology and maintain brain homeostasis. Conversely, the dysregulation and dysfunction of the NVU is an essential pathological feature that underlies neurological disorders spanning from chronic neurodegeneration to acute cerebrovascular events such as ischemic stroke and cerebral hemorrhage, which were the focus of this review. We also discussed how common vascular risk factors of stroke predispose the NVU to pathological changes. We synthesized existing literature and first provided an overview of the basic structure and function of NVU, followed by knowledge of how these components remodel in response to ischemic stroke and brain hemorrhage. A greater understanding of the NVU dysfunction and remodeling will enable the design of targeted therapies and provide a valuable foundation for relevant research in this area.

Remnant Cholesterol and Dyslipidemia Are Risk Factors for Guillain–Barré Syndrome and Severe Guillain–Barré Syndrome by Promoting Monocyte Activation

Background

Guillain–Barré syndrome (GBS) is the most common severe acute paralytic neuropathy, with a mortality rate of 5% and permanent sequelae rate of 10%. Currently, the cause of GBS remains unclear. Therefore, we sought to determine potential predictors for GBS and its severity.

Methods

A case–control study was performed at Tiantan Hospital in Beijing from January 2017 to December 2021. Laboratory and clinical characteristics were assessed in recruited GBS patients and healthy control individuals (matched by sex and age). The potential risk factors for GBS and severe GBS were assessed using a logistic regression analysis. The mRNA levels of toll-like receptor 4 (TLR4), toll-like receptor 2 (TLR2) and nuclear factor κB (NF-κB) in GBS patients and control PBMCs were detected by fluorescence quantitative PCR. THP-1 cells were costimulated with LPS and free cholesterol to demonstrate the effect of free cholesterol on monocyte activation.

Results

A total of 147 GBS patients and 153 healthy individuals were included in the study. Logistic regression analyses showed that preceding infection, alcohol consumption, remnant cholesterol, homocysteine and the dyslipidemia index were correlated with a higher risk of GBS. In contrast, increased HDL cholesterol was correlated with a lower risk of GBS. Moreover, remnant cholesterol and the dyslipidemia index were significantly correlated with severe GBS. The mRNA levels of TLR4, TLR2 and NF-κB in the PBMCs of GBS patients were significantly higher than those of healthy individuals. LPS activated THP-1 cells, and free cholesterol treatment increased the expression of TLR4, TLR2, NF-κB and IL-1β mRNA in LPS-activated THP-1 cells.

Conclusion

Dyslipidemia was correlated with the risk of GBS and severe GBS. Remnant cholesterol may promote the activation of monocytes in GBS patients. It may be valuable to control lipid levels in the prevention of GBS and severe GBS.

Oxysterols and Oxysterol Sulfates in Alzheimer’s Disease Brain and Cerebrospinal Fluid

Background:

Brain cholesterol levels are tightly regulated but increasing evidence indicates that cholesterol metabolism may drive Alzheimer’s disease (AD)-associated pathological changes. Recent advances in understanding of mitochondrial dysfunction in AD brain have presented a vital role played by mitochondria in oxysterol biosynthesis and their involvement in pathophysiology. Oxysterol accumulation in brain is controlled by various enzymatic pathways including sulfation. While research into oxysterol is under the areas of active investigation, there is less evidence for oxysterol sulfate levels in human brain.

Objective:

This study investigates the hypothesis that AD brain oxysterol detoxification via sulfation is impaired in later stages of disease resulting in oxysterol accumulation.

Methods:

Lipids were extracted from postmortem frozen brain tissue and cerebrospinal (CSF) from late- (Braak stage III-IV) and early- (Braak stage I-II) stage AD patients. Samples were spiked with internal standards prior to lipid extraction. Oxysterols were enriched with a two-step solid phase extraction using a polymeric SPE column and further separation was achieved by LC-MS/MS.

Results:

Oxysterols, 26-hydroxycholesterol (26-OHC), 25-hydroxycholesterol (25-OHC), and 7-oxycholesterol levels were higher in brain tissue and mitochondria extracted from late-stage AD brain tissue except for 24S-hydroxycholesterol, which was decreased in late AD. However, oxysterol sulfates are significantly lower in the AD frontal cortex. Oxysterols, 25-OHC, and 7-oxocholesterol was higher is CSF but 26-OHC and oxysterol sulfate levels were not changed.

Conclusion:

Our results show oxysterol metabolism is altered in AD brain mitochondria, favoring synthesis of 26-OHC, 25-OHC, and 7-oxocholesterol, and this may influence brain mitochondrial function and acceleration of the disease.

Association of F2-isoprostane levels with Alzheimer's disease in observational studies: A systematic review and meta-analysis

INTRODUCTION

The association between F₂-isoprostanes and Alzheimer's disease (AD) has been controversially discussed in the literature since the 1990s. However, no systematic review has been performed so far.

METHODS

A systematic review of observational studies on the associations of F₂-isoprostanes and the specific biomarker 8-iso-prostaglandin F_2α with AD were conducted. Random-effects model meta-analyses were performed.

RESULTS

29 studies were included in the systematic review, including four longitudinal studies. In an overall meta-analysis of the 25 cross-sectional studies, F₂-isoprostane levels were statistically significantly associated with AD (Hedge's g [95% confidence interval]: 1.00 [0.69-1.32]). When studies were grouped by biomarker and sample specimen, F₂-isoprostane and 8-iso-prostaglandin F_2α levels were statistically significantly elevated in tissue samples of the frontal lobe of AD patients. Moreover, F₂-isoprostane levels in cerebrospinal fluid and 8-iso-prostaglandin F_2α levels in blood samples of AD patients were significantly increased. Meta-analyses of the few longitudinal studies did not reach statistical significance.

DISCUSSION

Increased concentrations of F₂-isoprostanes were found in AD patients. However, due to the lack of adjustment in most cross-sectional case-control studies, results must be interpreted carefully. In addition, the causality of the association is uncertain because evidence from well-conducted longitudinal studies was conflicting, and further longitudinal studies are required to reinforce the results.

Vascular Dementia and Crosstalk Between the Complement and Coagulation Systems

Vascular Dementia (VaD) is a neurocognitive disorder caused by reduced blood flow to the brain tissue, resulting in infarction, and is the second most common type of dementia. The complement and coagulation systems are evolutionary host defence mechanisms activated by acute tissue injury to induce inflammation, clot formation and lysis; recent studies have revealed that these systems are closely interlinked. Overactivation of these systems has been recognised to play a key role in the pathogenesis of neurological disorders such as Alzheimer's disease and multiple sclerosis, however their role in VaD has not yet been extensively reviewed. This review aims to bridge the gap in knowledge by collating current understanding of VaD to enable identification of complement and coagulation components involved in the pathogenesis of this disorder that may have their effects amplified or supressed by crosstalk. Exploration of these mechanisms may unveil novel therapeutic targets or biomarkers that would improve current treatment strategies for VaD.

Cholesterol Dysmetabolism in Alzheimer's Disease: A Starring Role for Astrocytes?

In recent decades, the impairment of cholesterol metabolism in the pathogenesis of Alzheimer’s disease (AD) has been intensively investigated, and it has been recognized to affect amyloid β (Aβ) production and clearance, tau phosphorylation, neuroinflammation and degeneration. In particular, the key role of cholesterol oxidation products, named oxysterols, has emerged. Brain cholesterol metabolism is independent from that of peripheral tissues and it must be preserved in order to guarantee cerebral functions. Among the cells that help maintain brain cholesterol homeostasis, astrocytes play a starring role since they deliver de novo synthesized cholesterol to neurons. In addition, other physiological roles of astrocytes are to modulate synaptic transmission and plasticity and support neurons providing energy. In the AD brain, astrocytes undergo significant morphological and functional changes that contribute to AD onset and development. However, the extent of this contribution and the role played by oxysterols are still unclear. Here we review the current understanding of the physiological role exerted by astrocytes in the brain and their contribution to AD pathogenesis. In particular, we focus on the impact of cholesterol dysmetabolism on astrocyte functions suggesting new potential approaches to develop therapeutic strategies aimed at counteracting AD development.

Apolipoprotein A1, the neglected relative of Apolipoprotein E and its potential role in Alzheimer's disease

Lipoproteins are multi-molecule assemblies with the primary function of transportation and processing of lipophilic substances within aqueous bodily fluids (blood, cerebrospinal fluid). Nevertheless, they also exert other physiological functions such as immune regulation. In particular, neurons are both sensitive to uncontrolled responses of the immune system and highly dependent on a controlled and sufficient supply of lipids. For this reason, the role of certain lipoproteins and their protein-component (apolipoproteins, Apo's) in neurological diseases is perceivable. ApoE, for example, is well-accepted as one of the major risk factors for sporadic Alzheimer's disease with a protective allele variant (ε2) and a risk-causing allele variant (ε4). ApoA1, the major protein component of high-density lipoproteins, is responsible for transportation of excess cholesterol from peripheral tissues to the liver. The protein is synthesized in the liver and intestine but also can enter the brain via the choroid plexus and thereby might have an impact on brain lipid homeostasis. This review focuses on the role of ApoA1 in Alzheimer's disease and discusses whether its role within this neurodegenerative disorder is specific or represents a general neuroprotective mechanism.

A Tau-Driven Adverse Outcome Pathway Blueprint Toward Memory Loss in Sporadic (Late-Onset) Alzheimer's Disease with Plausible Molecular Initiating Event Plug-Ins for Environmental Neurotoxicants

The worldwide prevalence of sporadic (late-onset) Alzheimer's disease (sAD) is dramatically increasing. Aging and genetics are important risk factors, but systemic and environmental factors contribute to this risk in a still poorly understood way. Within the frame of BioMed21, the Adverse Outcome Pathway (AOP) concept for toxicology was recommended as a tool for enhancing human disease research and accelerating translation of data into human applications. Its potential to capture biological knowledge and to increase mechanistic understanding about human diseases has been substantiated since. In pursuit of the tau-cascade hypothesis, a tau-driven AOP blueprint toward the adverse outcome of memory loss is proposed. Sequences of key events and plausible key event relationships, triggered by the bidirectional relationship between brain cholesterol and glucose dysmetabolism, and contributing to memory loss are captured. To portray how environmental factors may contribute to sAD progression, information on chemicals and drugs, that experimentally or epidemiologically associate with the risk of AD and mechanistically link to sAD progression, are mapped on this AOP. The evidence suggests that chemicals may accelerate disease progression by plugging into sAD relevant processes. The proposed AOP is a simplified framework of key events and plausible key event relationships representing one specific aspect of sAD pathology, and an attempt to portray chemical interference. Other sAD-related AOPs (e.g., Aβ-driven AOP) and a better understanding of the impact of aging and genetic polymorphism are needed to further expand our mechanistic understanding of early AD pathology and the potential impact of environmental and systemic risk factors.

Omega-3 fatty acids are associated with blood-brain barrier integrity in a healthy aging population

In aging populations, omega-3 polyunsaturated fatty acids (PUFAs) have been associated with better cognitive function, slower rates of cognitive decline, and lower risk of developing dementia. Animal studies have shown that diets rich in omega-3 PUFAs reduce blood-brain barrier (BBB) disruption associated with aging, but this has yet to be observed in humans. Forty-five healthy subjects (mean age, 76 years) were recruited and underwent cognitive assessment (verbal learning and memory, language, processing speed, executive function, and motor control) and measurement of PUFAs. Forty of the same subjects also underwent magnetic resonance imaging (MRI) to measure BBB integrity (K_trans using dynamic contrast-enhanced MRI). The long chain omega-3 score (DHA+EPA) was negatively correlated with K_trans values in the internal capsule, indicating higher omega-3 levels were associated with greater BBB integrity in this region (r = -0.525, p = .004). Trends were observed for a positive correlation between the long chain omega-3 score and both memory and language scores, but not with executive function, speed, or motor control. The omega-6 score was not significantly correlated with any cognitive scores or K_trans values. The significant correlations between long chain omega-3 levels and BBB integrity provide a possible mechanism by which omega-3 PUFAs are associated with brain health.

Nutritional cognitive neuroscience of aging: Focus on carotenoids and cognitive frailty

The term „nutritional cognitive neuroscience” was recently established to define a research field focusing on the impact of nutrition on cognition and brain health across the life span. In this overview, we summarize the robust evidence on the role of carotenoids as micronutrients with different biological properties in persons with cognitive (pre)frailty. As neurodegenerative processes during aging occur in a continuum from brain aging to dementia, we propose the name „nutritional cognitive neuroscience of aging“ to define research on the role of nutrition and micronutrients in cognitive frailty. Further studies are warranted which integrate carotenoid interventions in multidomain, personalized lifestyle strategies.

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Cognitive integrity is an essential element of healthy and active ageing.

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Oxidative distress is strongly linked to neurodegeneration.

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Consumption and levels of carotenoids are linked to cognitive frailty.

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There is conflict of evidence for intervention trials with carotenoids in dementia.

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Future studies with carotenoids should be within personalized and multidomain strategies.

The Controversial Role of 24-S-Hydroxycholesterol in Alzheimer's Disease

The development of Alzheimer’s disease (AD) is influenced by several events, among which the dysregulation of cholesterol metabolism in the brain plays a major role. Maintenance of brain cholesterol homeostasis is essential for neuronal functioning and brain development. To maintain the steady-state level, excess brain cholesterol is converted into the more hydrophilic metabolite 24-S-hydroxycholesterol (24-OHC), also called cerebrosterol, by the neuron-specific enzyme CYP46A1. A growing bulk of evidence suggests that cholesterol oxidation products, named oxysterols, are the link connecting altered cholesterol metabolism to AD. It has been shown that the levels of some oxysterols, including 27-hydroxycholesterol, 7β-hydroxycholesterol and 7-ketocholesterol, significantly increase in AD brains contributing to disease progression. In contrast, 24-OHC levels decrease, likely due to neuronal loss. Among the different brain oxysterols, 24-OHC is certainly the one whose role is most controversial. It is the dominant oxysterol in the brain and evidence shows that it represents a signaling molecule of great importance for brain function. However, numerous studies highlighted the potential role of 24-OHC in favoring AD development, since it promotes neuroinflammation, amyloid β (Aβ) peptide production, oxidative stress and cell death. In parallel, 24-OHC has been shown to exert several beneficial effects against AD progression, such as preventing tau hyperphosphorylation and Aβ production. In this review we focus on the current knowledge of the controversial role of 24-OHC in AD pathogenesis, reporting a detailed overview of the findings about its levels in different AD biological samples and its noxious or neuroprotective effects in the brain. Given the relevant role of 24-OHC in AD pathophysiology, its targeting could be useful for disease prevention or slowing down its progression.

Phytosterols: Targeting Neuroinflammation in Neurodegeneration

Plant-derived sterols, phytosterols, are well known for their cholesterol-lowering activity in serum and their anti-inflammatory activities. Recently, phytosterols have received considerable attention due to their beneficial effects on various non-communicable diseases, and recommended use as daily dietary components. The signaling pathways mediated in the brain by phytosterols have been evaluated, but little is known about their effects on neuroinflammation, and no clinical studies have been undertaken on phytosterols of interest. In this review, we discuss the beneficial roles of phytosterols, including their attenuating effects on inflammation, blood cholesterol levels, and hallmarks of the disease, and their regulatory effects on neuroinflammatory disease pathways. Despite recent advancements made in phytosterol pharmacology, some critical questions remain unanswered. Therefore, we have tried to highlight the potential of phytosterols as viable therapeutics against neuroinflammation and to direct future research with respect to clinical applications.

Tucumã (Astrocaryum aculeatum) prevents memory loss and oxidative imbalance in the brain of rats with hyperlipidemia

Hyperlipidemia generates deposition of lipids, inflammation, and oxidative damage in cells and tissues, including those of the brain. Tucumã (Astrocaryum aculeatum) fruits contain bioactive compounds with antioxidant and anti-inflammatory effects. We evaluated the action of Tucumã extract on memory and brain cortex redox balance in hyperlipidemic rats. For 30 days, Wistar rats received Tucumã extract (250 mg/kg). Then, hyperlipidemia was induced by intraperitoneal administration of Poloxamer-407. Twenty-four hours later, the object recognition index was measured. The animals were euthanized for sample collection 36 hr postinduction. Hyperlipidemic animals showed memory loss and an imbalance between reactive species and intrinsic antioxidants. We found that Tucumã prevented memory loss and protein and lipid oxidative damage and prompted a better antioxidant response in the cerebral cortex of rats with hyperlipidemia. These findings suggest a neuroprotective effect and nutraceutical potential of Tucumã. PRACTICAL APPLICATIONS: In the present work, we demonstrated that induced hyperlipidemia in rats caused memory loss and redox unbalance, both factors prevented by the administration of Tucumã (Astrocaryum aculeatum) extract. Two aims were fulfilled with these results. The first was to show that hyperlipidemia affected brain function through oxidative damage and concerned basic research. The second was to offer a therapy that prevented this harm and could be applied in the clinic. Tucumã has ethnopharmacological importance through the consumption of fruits or the administration of extracts and oils by a population that was shown to enjoy improved health and longevity. Here, we show evidence that Tucumã contributes to the maintenance of brain health by preventing memory loss and oxidative damage, a nutraceutical supplement that may aid the prevention of vascular, inflammatory, and brain diseases.

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

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

Inflammation, Lipid (Per)oxidation, and Redox Regulation

Significance: Inflammation increases during the aging process. It is linked to mitochondrial dysfunction and increased reactive oxygen species (ROS) production. Mitochondrial macromolecules are critical targets of oxidative damage; they contribute to respiratory uncoupling with increased ROS production, redox stress, and a cycle of senescence, cytokine production, and impaired oxidative phosphorylation. Targeting the formation or accumulation of oxidized biomolecules, particularly oxidized lipids, in immune cells and mitochondria could be beneficial for age-related inflammation and comorbidities. Recent Advances: Inflammation is central to age-related decline in health and exhibits a complex relationship with mitochondrial redox state and metabolic function. Improvements in mass spectrometric methods have led to the identification of families of oxidized phospholipids (OxPLs), cholesterols, and fatty acids that increase during inflammation and which modulate nuclear factor erythroid 2-related factor 2 (Nrf2), peroxisome proliferator-activated receptor gamma (PPARγ), activator protein 1 (AP1), and NF-κB redox-sensitive transcription factor activity. Critical Issues: The kinetic and spatial resolution of the modified lipidome has profound and sometimes opposing effects on inflammation, promoting initiation at high concentration and resolution at low concentration of OxPLs. Future Directions: There is an emerging opportunity to prevent or delay age-related inflammation and vascular comorbidity through a resolving (oxy)lipidome that is dependent on improving mitochondrial quality control and restoring redox homeostasis.

Canine Models of Inherited Musculoskeletal and Neurodegenerative Diseases

Mouse models of human disease remain the bread and butter of modern biology and therapeutic discovery. Nonetheless, more often than not mouse models do not reproduce the pathophysiology of the human conditions they are designed to mimic. Naturally occurring large animal models have predominantly been found in companion animals or livestock because of their emotional or economic value to modern society and, unlike mice, often recapitulate the human disease state. In particular, numerous models have been discovered in dogs and have a fundamental role in bridging proof of concept studies in mice to human clinical trials. The present article is a review that highlights current canine models of human diseases, including Alzheimer's disease, degenerative myelopathy, neuronal ceroid lipofuscinosis, globoid cell leukodystrophy, Duchenne muscular dystrophy, mucopolysaccharidosis, and fucosidosis. The goal of the review is to discuss canine and human neurodegenerative pathophysiologic similarities, introduce the animal models, and shed light on the ability of canine models to facilitate current and future treatment trials.

Low high-density lipoprotein cholesterol and high triglycerides lipid profile in neuromyelitis optica spectrum disorder: Associations with disease activity and disability

BACKGROUND

Altered lipid metabolism is a feature of systemic autoimmune diseases. Dyslipidemia is associated with the disease activity and progression in patients with multiple sclerosis. However, in neuromyelitis optica spectrum disorder (NMOSD), changes in the lipid profile and the associations between specific lipid levels and disease activity/disability are unknown.

METHODS

Serum samples (N = 148) were collected from 53 patients with aquaporin-4 (AQP4)-positive NMOSD when they were not treated with lipid lowering agents. Fasting lipid (total cholesterol, triglyceride [TG], high-density lipoprotein cholesterol [HDL-C], low-density lipoprotein cholesterol) levels were compared between 39 patients with NMOSD, not taking steroids, and 142 age-, sex-, and body mass index-matched healthy controls. In addition, we analyzed the differences in the lipid profile between attack and remission samples and the associations between lipid profiles and clinical outcome in all 148 samples from 53 patients. The generalized estimating equation was used.

RESULTS

Patients with NMOSD showed lower HDL-C and higher TG levels compared to healthy controls (p = 0.017 and p < 0.001, respectively). HDL-C level was significantly lower during attack than remission (β = -7.851; p = 0.035), and TG level had positive correlation with EDSS scores (β = 0.014; p = 0.002) regardless of disease activity status. However, enhanced lesions on magnetic resonance imaging were not associated with lipid profiles.

CONCLUSION

Dyslipidemia with low HDL-C and high TG correlated disease activity and disability in AQP4-positive NMOSD. It remains to be elucidated whether altered lipid metabolism contributes to deleterious immune response, possibly through inflammation, or is secondary to neurological disability in NMOSD.

Localisation of oxysterols at the sub-cellular level and in biological fluids

Oxysterols are oxidized derivatives of cholesterol that are formed enzymatically or via reactive oxygen species or both. Cholesterol or oxysterols ingested as food are absorbed and packed into lipoproteins that are taken up by hepatic cells. Within hepatic cells, excess cholesterol is metabolised to form bile acids. The endoplasmic reticulum acts as the main organelle in the bile acid synthesis pathway. Metabolised sterols originating from this pathway are distributed within other organelles and in the cell membrane. The alterations to membrane oxysterol:sterol ratio affects the integrity of the cell membrane. The presence of oxysterols changes membrane fluidity and receptor orientation. It is well documented that hydroxylase enzymes located in mitochondria facilitate oxysterol production via an acidic pathway. More recently, the presence of oxysterols was also reported in lysosomes. Peroxisomal deficiencies favour intracellular oxysterols accumulation. Despite the low abundance of oxysterols compared to cholesterol, the biological actions of oxysterols are numerous and important. Oxysterol levels are implicated in the pathogenesis of multiple diseases ranging from chronic inflammatory diseases (atherosclerosis, Alzheimer's disease and bowel disease), cancer and numerous neurodegenerative diseases. In this article, we review the distribution of oxysterols in sub-cellular organelles and in biological fluids.

miRNA 933 Expression by Endothelial Cells is Increased by 27-Hydroxycholesterol and is More Prevalent in Plasma from Dementia Patients

Alzheimer’s disease (AD) etiology is complex; gene and environmental risk factors may interact to predispose to disease. From single nucleotide polymorphism analyses and genome-wide association studies, a number of candidate risk genes for the onset of AD have been identified and cluster around lipid metabolism and inflammation. We hypothesized that endothelial cells which line the blood-brain barrier are likely to be critical mediators of systemic metabolism within the brain. Therefore, we have studied the effect of 27 hydroxycholesterol (27-OHC) on microvascular endothelial cell (HMVEC) redox state, inflammatory cytokine secretion, and microRNA (miR) expression. Using a transwell method, we have studied directional secretion profiles for the proinflammatory cytokines TNFα and IL-6 and confirmed that 27-OHC induces discrete and directional inflammatory molecular signatures from HMVEC. The lipids caused depletion of cellular glutathione and cytokine secretion is HMVEC-redox state-dependent. Discovery miR expression change in HMVEC with and without 27-OHC treatment was undertaken. We selected three genes for further analysis by qPCR; miR-144 and 146 expression, which are anti-inflammatory and redox regulating modulators, were not affected significantly by 27-OHC. However, increased expression of a putative neurotrophic regulatory factor miR933 in HMVEC with 27-OHC was confirmed by qPCR. In plasma from patients with dementia, all three miR were found at significantly elevated levels compared to healthy older adults. These data highlight that 27-OHC has an important regulatory effect on endothelial microvascular cells to increase expression of a miR (–933) and secretion of inflammatory cytokines that are elevated in plasma from dementia patients.

Triptolide Improves Cognitive Dysfunction in Rats with Vascular Dementia by Activating the SIRT1/PGC-1α Signaling Pathway

Tripterygium Wilfordii Hook F has been exploited as a treatment for several diseases due to its neuroprotective, anti-tumor, and anti-inflammatory effects. Triptolide is one of its key bioactive compounds. Currently, the role of triptolide in cognitive dysfunction remains unclear. Here, the role of triptolide on cognitive dysfunction was investigated using chronic cerebral hypoperfusion-induced vascular dementia (VD) rat model. SD rats were administrated with Triptolide (5 μg/kg) for 6 weeks after undergoing permanent bilateral common carotid artery occlusion. The results show that triptolide treatment conferred neuroprotective effects in VD rats. Intraperitoneal injection of triptolide attenuated oxidative stress, learning and memory deficits, and neuronal apoptosis in the hippocampi. Moreover, triptolide enhanced the expression of SIRT1, PGC-1α, ZO-1, Claudin-5, and decreased the serum levels of NSE and S100B significantly. It also improved CCH-induced learning and memory deficits, and this is attributed to its capacity to promote SIRT1/PGC-1α signaling, confer antioxidant effects, and inhibit neuronal apoptosis. These findings indicate that triptolide may be an effective therapeutic agent for vascular cognitive dysfunction.

A Crosstalk Between Brain Cholesterol Oxidation and Glucose Metabolism in Alzheimer's Disease

In Alzheimer’s disease (AD), both cholesterol and glucose dysmetabolism precede the onset of memory deficit and contribute to the disease’s progression. It is indeed now believed that oxidized cholesterol in the form of oxysterols and altered glucose uptake are the main triggers in AD affecting production and clearance of Aβ, and tau phosphorylation. However, only a few studies highlight the relationship between them, suggesting the importance of further extensive studies on this topic. Recently, a molecular link was demonstrated between cholesterol oxidative metabolism and glucose uptake in the brain. In particular, 27-hydroxycholesterol, a key linker between hypercholesterolemia and the increased AD risk, is considered a biomarker for reduced glucose metabolism. In fact, its excess increases the activity of the renin-angiotensin system in the brain, thus reducing insulin-mediated glucose uptake, which has a major impact on brain functioning. Despite this important evidence regarding the role of 27-hydroxycholesterol in regulating glucose uptake by neurons, the involvement of other cholesterol oxidation products that have been clearly demonstrated to be key players in AD cannot be ruled out. This review highlights the current understanding of the potential role of cholesterol and glucose dysmetabolism in AD progression, and the bidirectional crosstalk between these two phenomena.

Emerging molecular mechanisms of vascular dementia

PURPOSE OF REVIEW

Microvascular ischemic disease of the brain is a common cause of cognitive impairment and dementia, particularly in the context of preexisting cardiovascular risk factors and aging. This review summarizes our current understanding of the emerging molecular themes that underlie progressive and irreparable vascular disease leading to neuronal tissue injury and dementia.

RECENT FINDINGS

Cardiometabolic risk factors including diabetes and hypertension are known to contribute to vascular disease. Currently, the impact of these risk factors on the integrity and function of the brain vasculature has been target of intense investigation. Molecularly, the consequences associated with these risk factors indicate that reactive oxygen species are strong contributors to cerebrovascular dysfunction and injury. In addition, genetic linkage analyses have identified penetrant monogenic causes of vascular dementia. Finally, recent reports begun to uncover a large number of polymorphisms associated with a higher risk for cerebrovascular disease.

SUMMARY

A comprehensive picture of key risk factors and genetic predispositions that contribute to brain microvascular disease and result in vascular dementia is starting to emerge. Understanding their relationships and cross-interactions will significantly aid in the development of preventive and intervention strategies for this devastating condition.

Pneumococcal Immunization Reduces Neurological and Hepatic Symptoms in a Mouse Model for Niemann-Pick Type C1 Disease

Niemann-Pick type C1 (NPC1) disease is caused by a deleterious mutation in the Npc1 gene, causing lysosomal accumulation of unesterified cholesterol and sphingolipids. Consequently, NPC1 disease patients suffer from severe neurovisceral symptoms which, in the absence of effective treatments, result in premature death. NPC1 disease patients display increased plasma levels of cholesterol oxidation products such as those enriched in oxidized low-density lipoprotein (oxLDL), a pro-inflammatory mediator. While it has been shown that inflammation precedes and exacerbates symptom severity in NPC1 disease, it is unclear whether oxLDL contributes to NPC1 disease progression. In this study, we investigated the effects of increasing anti-oxLDL IgM autoantibodies on systemic and neurological symptoms in an NPC1 disease mouse model. For this purpose, Npc1^nih mice were immunized with heat-inactivated S. pneumoniae, an immunogen which elicits an IgM autoantibody-mediated immune response against oxLDL. Npc1^nih mice injected with heat-inactivated pneumococci displayed an improved hepatic phenotype, including liver lipid accumulation and inflammation. In addition, regression of motor skills was delayed in immunized Npc1^nih. In line with these results, brain analyses showed an improved cerebellar phenotype and neuroinflammation in comparison with control-treated subjects. This study highlights the potential of the pneumococcal immunization as a novel therapeutical approach in NPC1 disease. Future research should investigate whether implementation of this therapy can improve life span and quality of life of NPC1 disease patients.

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

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

Cholesterol intake and statin use regulate neuronal G protein-gated inwardly rectifying potassium channels

Cholesterol, a critical component of the cellular plasma membrane, is essential for normal neuronal function. Cholesterol content is highest in the brain, where most cholesterol is synthesized de novo; HMG-CoA reductase controls the synthesis rate. Despite strict control, elevated blood cholesterol levels are common and are associated with various neurological disorders. G protein-gated inwardly rectifying potassium (GIRK) channels mediate the actions of inhibitory brain neurotransmitters. Loss of GIRK function enhances neuron excitability; gain of function reduces neuronal activity. However, the effect of dietary cholesterol or HMG-CoA reductase inhibition (i.e., statin therapy) on GIRK function remains unknown. Using a rat model, we compared the effects of a high-cholesterol versus normal diet both with and without atorvastatin, a widely prescribed HMG-CoA reductase inhibitor, on neuronal GIRK currents. The high-cholesterol diet increased hippocampal CA1 region cholesterol levels and correspondingly increased neuronal GIRK currents. Both phenomena were reversed by cholesterol depletion in vitro. Atorvastatin countered the high-cholesterol diet effects on neuronal cholesterol content and GIRK currents; these effects were reversed by cholesterol enrichment in vitro. Our findings suggest that high-cholesterol diet and atorvastatin therapy affect ion channel function in the brain by modulating neuronal cholesterol levels.

Effect of Cholesterol on Membrane Fluidity and Association of Aβ Oligomers and Subsequent Neuronal Damage: A Double-Edged Sword

Background: The beta-amyloid peptide (Aβ) involved in Alzheimer's disease (AD) has been described to associate/aggregate on the cell surface disrupting the membrane through pore formation and breakage. However, molecular determinants involved for this interaction (e.g., some physicochemical properties of the cell membrane) are largely unknown. Since cholesterol is an important molecule for membrane structure and fluidity, we examined the effect of varying cholesterol content with the association and membrane perforation by Aβ in cultured hippocampal neurons. Methods: To decrease or increase the levels of cholesterol in the membrane we used methyl-β-cyclodextrin (MβCD) and MβCD/cholesterol, respectively. We analyzed if membrane fluidity was affected using generalized polarization (GP) imaging and the fluorescent dye di-4-ANEPPDHQ. Additionally membrane association and perforation was assessed using immunocytochemistry and electrophysiological techniques, respectively. Results: The results showed that cholesterol removal decreased the macroscopic association of Aβ to neuronal membranes (fluorescent-puncta/20 μm: control = 18 ± 2 vs. MβCD = 10 ± 1, p < 0.05) and induced a facilitation of the membrane perforation by Aβ with respect to control cells (half-time for maximal charge transferred: control = 7.2 vs. MβCD = 4.4). Under this condition, we found an increase in membrane fluidity (46 ± 3.3% decrease in GP value, p < 0.001). On the contrary, increasing cholesterol levels incremented membrane rigidity (38 ± 2.7% increase in GP value, p < 0.001) and enhanced the association and clustering of Aβ (fluorescent-puncta/20 μm: control = 18 ± 2 vs. MβCD = 10 ± 1, p < 0.01), but inhibited membrane disruption. Conclusion: Our results strongly support the significance of plasma membrane organization in the toxic effects of Aβ in hippocampal neurons, since fluidity can regulate distribution and insertion of the Aβ peptide in the neuronal membrane.

Dapsone protects brain microvascular integrity from high-fat diet induced LDL oxidation

Atherosclerosis was considered to induce many vascular-related complications, such as acute myocardial infarction and stroke. Abnormal lipid metabolism and its peroxidation inducing blood–brain barrier (BBB) leakage were associated with the pre-clinical stage of stroke. Dapsone (DDS), an anti-inflammation and anti-oxidation drug, has been found to have protective effects on vascular. However, whether DDS has a protective role on brain microvessels during lipid oxidation had yet to be elucidated. We investigated brain microvascular integrity in a high-fat diet (HFD) mouse model. We designed this study to explore whether DDS had protective effects on brain microvessels under lipid oxidation and tried to explain the underlying mechanism. In our live optical study, we found that DDS significantly attenuated brain microvascular leakage through reducing serum oxidized low-density lipoprotein (oxLDL) in HFD mice (p < 0.001), and DDS significantly inhibited LDL oxidation in vitro (p < 0.001). Our study showed that DDS protected tight junction proteins: ZO-1 (p < 0.001), occludin (p < 0.01), claudin-5 (p < 0.05) of microvascular endothelial cells in vivo and in vitro. DDS reversed LAMP1 aggregation in cytoplasm, and decreased the destruction of tight junction protein: ZO-1 in vitro. We first revealed that DDS had a protective role on cerebral microvessels through preventing tight junction ZO-1 from abnormal degradation by autophagy and reducing lysosome accumulation. Our findings suggested the significance of DDS in protecting brain microvessels under lipid metabolic disorders, which revealed a novel potential therapeutic strategy in brain microvascular-related diseases.

Pro- and Anti-inflammatory Effects of High Cholesterol Diet on Aged Brain

Both hypercholesterolemia and aging are related to cognitive decline or Alzheimer's disease. However, their interactive influence on the neurodegenerative progress remains unclear. To address this issue, 6-month-old and 16-month-old female mice were fed a 3% cholesterol diet for 8 weeks, followed by hippocampus-related functional, pathological, biochemical and molecular analyses. The high cholesterol diet did not exacerbate age-dependent cognitive decline and hippocampal neuronal death, and even greatly mitigated decreases of synaptophysin and growth associated protein 43 expression in the hippocampus of aged mice. Compared with young controls, aged mice fed normal diet showed mild activation of hippocampal microglia with increased expression of CD68, a marker of the microglial M1 phenotype, and decreased expression of CD206, a marker of the microglial M2 phenotype. More interestingly, the high cholesterol diet not only improved NLRP3 inflammasome activation and IL-1β expression, but also increased levels of anti-inflammatory cytokines IL-4 and IL-6 in the hippocampus of old mice, suggesting playing pro- and anti-neuroinflammatory effects. In addition, the cholesterol rich diet resulted in a defect of the blood-brain barrier of aged hippocampus, as revealed by increased brain albumin content. These results have revealed both harmful and protective effects of high cholesterol diet on aged brain, which helps us to understand that hypercholesterolemia in the aged population is not associated with dementia and cognitive impairment.

Theobromine-Induced Changes in A1 Purinergic Receptor Gene Expression and Distribution in a Rat Brain Alzheimer's Disease Model

Dementia caused by Alzheimer's disease (AD) is mainly characterized by accumulation in the brain of extra- and intraneuronal amyloid-β (Aβ) and tau proteins, respectively, which selectively affect specific regions, particularly the neocortex and the hippocampus. Sporadic AD is mainly caused by an increase in apolipoprotein E, a component of chylomicrons, which are cholesterol transporters in the brain. Recent studies have shown that high lipid levels, especially cholesterol, are linked to AD. Adenosine is an atypical neurotransmitter that regulates a wide range of physiological functions by activating four P1 receptors (A1, A2A, A2B, and A3) and P2 purinergic receptors that are G protein-coupled. A1 receptors are involved in the inhibition of neurotransmitter release, which could be related to AD. The aim of the present work was to study the effects of a lard-enriched diet (LED) on cognitive and memory processes in adult rats (6 months of age) as well as the effect of theobromine on these processes. The results indicated that the fat-enriched diet resulted in a long-term deterioration in cognitive and memory functions. Increased levels of Aβ protein and IL-1β were also observed in the rats fed with a high-cholesterol diet, which were used to validate the AD animal model. In addition, the results of qPCR and immunohistochemistry indicated a decrease in gene expression and distribution of A1 purinegic receptor, respectively, in the hippocampus of LED-fed rats. Interestingly, theobromine, at both concentrations tested, restored A1 receptor levels and improved cognitive functions and Aβ levels for a dose of 30 mg/L drinking water.

Effect of Cholesterol on Membrane Fluidity and Association of Aβ Oligomers and Subsequent Neuronal Damage: A Double-Edged Sword

Background: The beta-amyloid peptide (Aβ) involved in Alzheimer's disease (AD) has been described to associate/aggregate on the cell surface disrupting the membrane through pore formation and breakage. However, molecular determinants involved for this interaction (e.g., some physicochemical properties of the cell membrane) are largely unknown. Since cholesterol is an important molecule for membrane structure and fluidity, we examined the effect of varying cholesterol content with the association and membrane perforation by Aβ in cultured hippocampal neurons. Methods: To decrease or increase the levels of cholesterol in the membrane we used methyl-β-cyclodextrin (MβCD) and MβCD/cholesterol, respectively. We analyzed if membrane fluidity was affected using generalized polarization (GP) imaging and the fluorescent dye di-4-ANEPPDHQ. Additionally membrane association and perforation was assessed using immunocytochemistry and electrophysiological techniques, respectively. Results: The results showed that cholesterol removal decreased the macroscopic association of Aβ to neuronal membranes (fluorescent-puncta/20 μm: control = 18 ± 2 vs. MβCD = 10 ± 1, p < 0.05) and induced a facilitation of the membrane perforation by Aβ with respect to control cells (half-time for maximal charge transferred: control = 7.2 vs. MβCD = 4.4). Under this condition, we found an increase in membrane fluidity (46 ± 3.3% decrease in GP value, p < 0.001). On the contrary, increasing cholesterol levels incremented membrane rigidity (38 ± 2.7% increase in GP value, p < 0.001) and enhanced the association and clustering of Aβ (fluorescent-puncta/20 μm: control = 18 ± 2 vs. MβCD = 10 ± 1, p < 0.01), but inhibited membrane disruption. Conclusion: Our results strongly support the significance of plasma membrane organization in the toxic effects of Aβ in hippocampal neurons, since fluidity can regulate distribution and insertion of the Aβ peptide in the neuronal membrane.

A Mini-Review of the NADPH oxidases in Vascular Dementia: Correlation with NOXs and Risk Factors for VaD

Oxidative stress (OS) is one of the factors that cause dementia conditions such as Alzheimer’s disease and vascular dementia (VaD). In the pathogenesis of VaD, OS is associated with risk factors that include increased age, hypertension, and stroke. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a molecular source of reactive oxygen species (ROS). According to recent studies, inhibition of NOX activity can reduce cognitive impairment in animal models of VaD. In this article, we review the evidence linking cognitive impairment with NOX-dependent OS, including the vascular NOX and non-vascular NOX systems, in VaD.

Blood-brain barrier dysfunction and recovery after ischemic stroke

The blood-brain barrier (BBB) plays a vital role in regulating the trafficking of fluid, solutes and cells at the blood-brain interface and maintaining the homeostatic microenvironment of the CNS. Under pathological conditions, such as ischemic stroke, the BBB can be disrupted, followed by the extravasation of blood components into the brain and compromise of normal neuronal function. This article reviews recent advances in our knowledge of the mechanisms underlying BBB dysfunction and recovery after ischemic stroke. CNS cells in the neurovascular unit, as well as blood-borne peripheral cells constantly modulate the BBB and influence its breakdown and repair after ischemic stroke. The involvement of stroke risk factors and comorbid conditions further complicate the pathogenesis of neurovascular injury by predisposing the BBB to anatomical and functional changes that can exacerbate BBB dysfunction. Emphasis is also given to the process of long-term structural and functional restoration of the BBB after ischemic injury. With the development of novel research tools, future research on the BBB is likely to reveal promising potential therapeutic targets for protecting the BBB and improving patient outcome after ischemic stroke.

European contribution to the study of ROS: A summary of the findings and prospects for the future from the COST action BM1203 (EU-ROS)

The European Cooperation in Science and Technology (COST) provides an ideal framework to establish multi-disciplinary research networks. COST Action BM1203 (EU-ROS) represents a consortium of researchers from different disciplines who are dedicated to providing new insights and tools for better understanding redox biology and medicine and, in the long run, to finding new therapeutic strategies to target dysregulated redox processes in various diseases. This report highlights the major achievements of EU-ROS as well as research updates and new perspectives arising from its members. The EU-ROS consortium comprised more than 140 active members who worked together for four years on the topics briefly described below. The formation of reactive oxygen and nitrogen species (RONS) is an established hallmark of our aerobic environment and metabolism but RONS also act as messengers via redox regulation of essential cellular processes. The fact that many diseases have been found to be associated with oxidative stress established the theory of oxidative stress as a trigger of diseases that can be corrected by antioxidant therapy. However, while experimental studies support this thesis, clinical studies still generate controversial results, due to complex pathophysiology of oxidative stress in humans. For future improvement of antioxidant therapy and better understanding of redox-associated disease progression detailed knowledge on the sources and targets of RONS formation and discrimination of their detrimental or beneficial roles is required. In order to advance this important area of biology and medicine, highly synergistic approaches combining a variety of diverse and contrasting disciplines are needed.

A 2-year Double-Blind RCT Follow-up Study with Fermented Papaya Preparation (FPP) Modulating Key Markers in Middle-Age Subjects with Clustered Neurodegenerative Disease-Risk Factors

In recent years a number of studies have reported the significant relationship between metabolic syndrome and neurodegenerative disease. There is accumulating evidence that the interplay of combined genetic and environmental risk factors (from diet to life style to pollutants) to intrinsic age-related oxi-inflammatory changes may be advocated for to explain the pandemic of neurodegenerative diseases. In recent years a specific Fermented Papaya Preparation (FPP) has been shown to significantly affect a number of redox signalling abnormalities in a variety of chronic diseases and as well in aging mechanisms either on experimental and on clinical ground. The aim of the present study was to evaluate FPP use in impending metabolic disease patients with potentially neurodegenerative disease clustered risk factors. The study population consisted of 90 patients aged 45-65 years old, with impending metabolic syndrome and previously selected as to be ApoE4 genotype negative. By applying a RCT, double-blind method, one group received FPP 4.5 g twice a day (the most common dosage utilized in prior clinical studies) while the other received an oral antioxidant cocktail (trans-resveratrol, selenium, vitamin E, vitamin C). Then, after 21 month treatment period, a selected heavy metal chelator was added at the dosage of 3 g/nocte for the final 3 months study treatment. The parameters tested were: routine tests oxidized LDL-cholesterol, anti-oxidised LDL, Cyclophilin-A (CyPA), plasminogen activator inhibitor-1 and CyPA gene expression. From this study it would appear that FPP, unlike the control antioxidant, significantly decreased oxidized-LDL and near normalizing the anti-Ox-LDL/Ox-LDL ratio (p<0.001) although unaffecting the lipid profile per sè. Moreover, only FPP decreased cyclophilin-A plasma level and plasminogen activator-inhibitor (p<0.01) together with downregulating cyclophilin-A gene expression (p<0.01). Insulin resistance was only mildly improved. Heavy metals gut clearance proved to be effectively enhanced by the chelator (p<0.01) and this was not affected by any of the nutraceuticals, nor it added any further benefit to the biological action of FPP.

Cholesterol up-regulates neuronal G protein-gated inwardly rectifying potassium (GIRK) channel activity in the hippocampus

Hypercholesterolemia is a well known risk factor for the development of neurodegenerative disease. However, the underlying mechanisms are mostly unknown. In recent years, it has become increasingly evident that cholesterol-driven effects on physiology and pathophysiology derive from its ability to alter the function of a variety of membrane proteins including ion channels. Yet, the effect of cholesterol on G protein-gated inwardly rectifying potassium (GIRK) channels expressed in the brain is unknown. GIRK channels mediate the actions of inhibitory brain neurotransmitters. As a result, loss of GIRK function can enhance neuron excitability, whereas gain of GIRK function can reduce neuronal activity. Here we show that in rats on a high-cholesterol diet, cholesterol levels in hippocampal neurons are increased. We also demonstrate that cholesterol plays a critical role in modulating neuronal GIRK currents. Specifically, cholesterol enrichment of rat hippocampal neurons resulted in enhanced channel activity. In accordance, elevated currents upon cholesterol enrichment were also observed in Xenopus oocytes expressing GIRK2 channels, the primary GIRK subunit expressed in the brain. Furthermore, using planar lipid bilayers, we show that although cholesterol did not affect the unitary conductance of GIRK2, it significantly enhanced the frequency of channel openings. Last, combining computational and functional approaches, we identified two putative cholesterol-binding sites in the transmembrane domain of GIRK2. These findings establish that cholesterol plays a critical role in modulating GIRK activity in the brain. Because up-regulation of GIRK function can reduce neuronal activity, our findings may lead to novel approaches for prevention and therapy of cholesterol-driven neurodegenerative disease.

Mechanisms of acupuncture on vascular dementia-A review of animal studies

Vascular dementia (VaD) is the second leading type of dementia after Alzheimer's disease plaguing the aging population. Acupuncture has served as alternative and complementary medicine in the world for a long time and its use for VaD is based on a large body of preclinical and clinical researches. The mechanisms that underlie the protective effects of acupuncture are slowly beginning to be understood. Acupuncture influences multiple aspects of the pathological process of VaD. It improves cognitive function through protecting cerebral neurons from oxidative stress, apoptosis, and neuroinflammation, regulating glucose metabolism and neurotransmitters. Acupuncture may also improve synaptic plasticity and blood vessel function. It is likely that no single factor can explain the protection provided by acupuncture. This review provides a comprehensive overview of established and recent findings in animal-based researches aiming to elucidate the complex mechanisms of acupuncture on VaD.

Changes in brain oxysterols at different stages of Alzheimer's disease: Their involvement in neuroinflammation

Alzheimer's disease (AD) is a gradually debilitating disease that leads to dementia. The molecular mechanisms underlying AD are still not clear, and at present no reliable biomarkers are available for the early diagnosis. In the last several years, together with oxidative stress and neuroinflammation, altered cholesterol metabolism in the brain has become increasingly implicated in AD progression. A significant body of evidence indicates that oxidized cholesterol, in the form of oxysterols, is one of the main triggers of AD. The oxysterols potentially most closely involved in the pathogenesis of AD are 24-hydroxycholesterol and 27-hydroxycholesterol, respectively deriving from cholesterol oxidation by the enzymes CYP46A1 and CYP27A1. However, the possible involvement of oxysterols resulting from cholesterol autooxidation, including 7-ketocholesterol and 7β-hydroxycholesterol, is now emerging. In a systematic analysis of oxysterols in post-mortem human AD brains, classified by the Braak staging system of neurofibrillary pathology, alongside the two oxysterols of enzymatic origin, a variety of oxysterols deriving from cholesterol autoxidation were identified; these included 7-ketocholesterol, 7α-hydroxycholesterol, 4β-hydroxycholesterol, 5α,6α-epoxycholesterol, and 5β,6β-epoxycholesterol. Their levels were quantified and compared across the disease stages. Some inflammatory mediators, and the proteolytic enzyme matrix metalloprotease-9, were also found to be enhanced in the brains, depending on disease progression. This highlights the pathogenic association between the trends of inflammatory molecules and oxysterol levels during the evolution of AD. Conversely, sirtuin 1, an enzyme that regulates several pathways involved in the anti-inflammatory response, was reduced markedly with the progression of AD, supporting the hypothesis that the loss of sirtuin 1 might play a key role in AD. Taken together, these results strongly support the association between changes in oxysterol levels and AD progression.