Possible modification of Alzheimer's disease by statins in midlife: interactions with genetic and non-genetic risk factors

Rosuvastatin attenuates total-tau serum levels and increases expression of miR-124-3p in dyslipidemic Alzheimer's patients: a historic cohort study

microRNAs are candidate diagnostic biomarkers for Alzheimer's disease. This study aimed to compare Silymarin with Rosuvastatin and placebo on total-Tau protein level and expression levels of microRNAs and TGF-β and COX-2 in Alzheimer's patients with secondary dyslipidemia. 36 mild AD patients with dyslipidemia were divided into three groups of 12. The first group received silymarin (140mg), the second group received placebo (140mg), and the third group recieved Rosuvastatin (10mg). Tablets were administered three times a day for Six months. The blood samples of the patients were collected before and after the intervention and the serum was separated. Using the RT-qPCR method, the expression levels of miR-124-3p and miR-125b-5p were assessed, and the serum levels of total-Tau, TGF-β, and COX-2 enzyme were measured using the ELISA method. Data were analyzed with SPSS software. In this study, the level of Δtotal-Tau was significantly lower in the Rosuvastatin group compared to the placebo (P = 0.038). Also, a significant reduction in the level of ΔTGF-β was observed in the Silymarin to Rosuvastatin group (p = 0.046) and ΔmiR-124-3p was significantly increased in the Rosuvastatin compared to the placebo group (p = 0.044). Rosuvastatin outperformed silymarin in decreasing Δtotal-Tau serum levels and enhancing expression of ΔmiR-124-3p, attributed to Rosuvastatin's capacity to lower cholesterol levels and inflammation concurrently. Conversely, silymarin was more effective than Rosuvastatin in reducing levels of ΔTGF-β. Serum miR-124-3p could serve as a promising diagnostic biomarker and a new therapeutic focus in AD.

Diabetes mellitus and Alzheimer's disease: Understanding disease mechanisms, their correlation, and promising dual activity of selected herbs

ETHNOPHARMACOLOGICAL RELEVANCE

This review explores the link between Type 2 Diabetes Mellitus (T2DM) and diabetes-induced Alzheimer's disease (AD). It emphasizes the shared pathophysiological links and mechanisms between the two conditions, focusing on reduced insulin levels and receptors, impaired glucose metabolism, insulin resistance, mitochondrial dysfunction, and oxidative damage in AD-affected brains-paralleling aspects of T2DM. The review suggests AD as a "diabetes of the brain," supported by cognitive enhancement through antidiabetic interventions. It focuses on the traditionally used Indian herbs as a means to manage both conditions while addressing developmental challenges.

AIM OF THE STUDY

This study explores the DM-AD connection, reviewing medicinal herbs with protective potential for both ailments, considering traditional uses and developmental challenges.

MATERIALS AND METHODS

Studied research, reviews, and ethnobotanical and scientific data from electronic databases and traditional books.

RESULTS

The study analyzes the pathophysiological links between DM and AD, emphasizing their interconnected factors. Eight Ayurvedic plants with dual protective effects against T2DM and AD are thoroughly reviewed with preclinical/clinical evidence. Historical context, phytoconstituents, and traditional applications are explored. Innovative formulations using these plants are examined. Challenges stemming from phytoconstituents' physicochemical properties are highlighted, prompting novel formulation development, including nanotechnology-based delivery systems. The study uncovers obstacles in formulating treatments for these diseases.

CONCLUSION

The review showcases the dual potential of chosen medicinal herbs against both diseases, along with their traditional applications, endorsing their use. It addresses formulation obstacles, proposing innovative delivery technologies for herbal therapies, while acknowledging their constraints. The review suggests the need for heightened investment and research in this area.

Oxidative stress is associated with Aβ accumulation in chronic sleep deprivation model

Amyloid-β (Aβ) accumulation is the main pathological change in Alzheimer's disease (AD), which results from the imbalance of production and clearance of Aβ in the brain. Our previous study found that chronic sleep deprivation (CSD) led to the deposition of Aβ in the brain by disrupting the balance of Aβ production and clearance, but the specific mechanism was not clear. In the present study, we investigated the effects of oxidative stress on Aβ accumulation in CSD rats. We found that the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) significantly increased after CSD, while superoxide dismutase (SOD) decreased in the brain. Furthermore, the serum ROS was elevated and SOD declined after CSD. The levels of oxidative stress in the brain were significantly correlated with β-site APP-cleaving enzyme 1 (BACE1), low-density lipoprotein receptor-related protein-1 (LRP1), and receptor of advanced glycation end products (RAGE) levels in hippocampus and prefrontal lobe, and the concentration of serum oxidative mediators were strongly correlated with plasma levels of soluble LRP1 (sLRP1) and soluble RAGE (sRAGE). These results suggested that the oxidative stress in the brain and serum may involved in the CSD-induced Aβ accumulation. The underlying mechanism may be associated with disrupting the balance of Aβ production and clearance.

Statins and risks of dementia among patients with heart failure: a population-based retrospective cohort study in Hong Kong

Background

Heart failure (HF) and dementia frequently co-exist with shared pathological mechanisms and risk factors. Our study aims to investigate the association between statin therapy and the risks of dementia and its subtypes among patients with HF.

Methods

The Hong Kong Clinical Data Analysis and Reporting System database was interrogated to identify patients with incident HF diagnosis from 2004 to 2018, using ICD 9/ICD 10 codes. Inverse probability of treatment weighting (IPTW) was used to balance baseline covariates between statin users (N = 54,004) and non-users (N = 50,291). The primary outcomes were incident all-cause dementia, including subtypes of Alzheimer's disease, vascular dementia, and unspecified dementia. Cox proportional-hazard model with competing risk regression was performed to estimate the sub-distribution hazards ratio (SHR) with corresponding 95% confidence intervals (CI) of the risks of all-cause dementia and its subtypes that are associated with statin use.

Findings

Of all eligible patients with HF (N = 104,295), the mean age was 74.2 ± 13.6 years old and 52,511 (50.3%) were male. Over a median follow-up of 9.9 years (interquartile range [IQR]: 6.4-13.0), 10,031 (9.6%) patients were diagnosed with dementia, among which Alzheimer's disease (N = 2250), vascular dementia (N = 1831), and unspecified dementia (N = 5950) were quantified separately. After IPTW, statin use was associated with a 20% lower risk of incident dementia compared with non-use (multivariable-adjusted SHR 0.80, 95% CI 0.76-0.84). Stratified by subtypes of dementia, statin use was associated with a 28% lower risk of Alzheimer's disease (SHR 0.72, 95% CI 0.63-0.82), 18% lower risk of vascular dementia (SHR 0.82, 95% CI 0.70-0.95), and a 20% lower risk of unspecified dementia (SHR 0.80, 95% CI 0.75-0.85).

Interpretation

In patients with HF, statin use was associated with a significantly lower risk of all-cause dementia and its subtypes, including Alzheimer's disease, vascular dementia, and unspecified dementia. Both randomized trials and experimental studies to validate the potential neuroprotective effect of statin are warranted.

Funding

No funding was provided for this study.

Re-Arranging the Puzzle between the Amyloid-Beta and Tau Pathology: An APP-Centric Approach

After several years of research in the field of Alzheimer's disease (AD), it is still unclear how amyloid-beta (Aβ) and Tau, two key hallmarks of the disease, mediate the neuropathogenic events that lead to AD. Current data challenge the "Amyloid Cascade Hypothesis" that has prevailed in the field of AD, stating that Aβ precedes and triggers Tau pathology that will eventually become the toxic entity in the progression of the disease. This perspective also led the field of therapeutic approaches towards the development of strategies that target Aβ or Tau. In the present review, we discuss recent literature regarding the neurotoxic role of both Aβ and Tau in AD, as well as their physiological function in the healthy brain. Consequently, we present studies suggesting that Aβ and Tau act independently of each other in mediating neurotoxicity in AD, thereafter, re-evaluating the "Amyloid Cascade Hypothesis" that places Tau pathology downstream of Aβ. More recent studies have confirmed that both Aβ and Tau could propagate the disease and induce synaptic and memory impairments via the amyloid precursor protein (APP). This finding is not only interesting from a mechanistic point of view since it provides better insights into the AD pathogenesis but also from a therapeutic point of view since it renders APP a common downstream effector for both Aβ and Tau. Subsequently, therapeutic strategies that act on APP might provide a more viable and physiologically relevant approach for targeting AD.

Does statin use affect amyloid beta deposition and brain metabolism?

BACKGROUND

There are contradictory findings regarding the effect of statin drugs on amyloid β (Aβ) deposition as one of the main hallmarks of Alzheimer's disease (AD), along with tau pathology. We aimed to longitudinally investigate the therapeutic and preventive role of statin drugs by examining the brain Aβ deposition and metabolism rate in AD, mild cognitive impairment (MCI), and healthy controls (HC).

METHODS

The data of 828 subjects including 178 HC, 492 MCI, and 158 AD individuals were obtained from ADNI. The baseline and longitudinal [18 F] AV45 and 18-fluorodeoxyglucose (FDG) PET standard uptake value ratio (SUVR) measures were investigated among statin users and non-users.

RESULTS

Our results showed that there is no significant difference in baseline Aβ deposition and metabolism rate between statin users and non-users among HC, MCI, and AD subjects. While there was no significant effect of statin on metabolism rate, there was a significant difference in Aβ deposition change after 4 years (from baseline) between statin users and non-users within HC subjects (p = 0.011). The change of Aβ deposition at 4 years from baseline was -2.0 ± 6.3% for statin users and 1.4 ± 4.7% for non-users. There was no significant association between statin duration use with baseline and longitudinal Aβ deposition and metabolism rate. However, statin dosage was significantly associated with Aβ deposition in 2 years (r = -0.412, p = 0.021) in the HC group. Moreover, our analysis showed a significant correlation between total statin exposure (duration×dosage) and Aβ deposition in 2 years visit (r = -0.198, p = 0.037) in HC subjects. Furthermore, we investigated the longitudinal changes within each group of statin users and non-users separately in linear mixed models. Our findings showed that there are no significant changes in AV45 and FDG SUVR among both groups.

CONCLUSION

The present longitudinal analysis revealed that using statins might be beneficial in slowing down or stabilizing the Aβ deposition due to aging in subjects without cognitive impairment. However, once the clinical symptoms of cognitive impairment appear, statins fail to slow down Aβ deposition. Overall, our findings revealed that statin users might have slower Aβ aggregation than non-users.

The effects of simvastatin and fenofibrate on malondialdehyde and reduced glutathione concentrations in the plasma, liver, and brain of normolipidaemic and hyperlipidaemic rats

The objective of study was to investigate the effects of different doses of simvastatin and fenofibrate on malondialdehyde (MDA) and reduced glutathione (GSH) in the plasma, liver, and brain tissue of male normolipidaemic and hyperlipidaemic rats. Normolipidaemic (Wistar) rats were receiving 10 or 50 mg/kg a day of simvastatin or 30 or 50 mg/kg a day of fenofibrate. Hyperlipidaemic (Zucker) rats were receiving 50 mg/kg/day of simvastatin or 30 mg/kg/day of fenofibrate. Control normolipidaemic and hyperlipidaemic rats were receiving saline. Simvastatin, fenofibrate, and saline were administered by gavage for three weeks. In normolipidaemic rats simvastatin and fenofibrate showed similar and dose-independent effects on plasma and brain MDA and GSH concentrations. Generally, plasma and brain MDA decreased, while brain GSH concentration increased. In hyperlipidaemic rats simvastatin did not affect plasma and brain MDA and GSH concentrations but significantly decreased liver GSH. Fenofibrate decreased plasma and liver MDA but increased brain MDA. In both rat strains fenofibrate significantly decreased liver GSH concentrations, most likely because fenofibrate metabolites bind to GSH. Our findings suggest that simvastatin acts as an antioxidant only in normolipidaemic rats, whereas fenofibrate acts as an antioxidant in both rat strains.

Treadmill Exercise Modulates Intestinal Microbes and Suppresses LPS Displacement to Alleviate Neuroinflammation in the Brains of APP/PS1 Mice

Neuroinflammation occurs throughout the pathogenesis of Alzheimer’s disease (AD). Here, we investigated the effects of treadmill exercise on neuroinflammation in APP/PS1 transgenic AD mice and the potential involvement of microbe–gut–brain axis (MGB) mechanisms based on growing evidence that AD’s pathogenesis is correlated with a deterioration in the function of gut microbiota. APP/PS1 transgenic AD mice were subjected to 12 weeks of treadmill exercise, followed by spatial memory tests. After the behavioral study, the amyloid (Aβ) pathology, gut microbes and metabolites, bacterial lipopolysaccharide (LPS) displacement, and degree of neuroinflammation were analyzed. We found that this strategy of exercise enriched gut microbial diversity and alleviated neuroinflammation in the brain. Notably, exercise led to reductions in pathogenic bacteria such as intestinal Allobaculum, increases in probiotic bacteria such as Akkermansia, increased levels of intestine–brain barrier proteins, and attenuated LPS displacement. These results suggest that prolonged exercise can effectively modulate gut microbes and the intestinal barrier and thereby reduce LPS displacement and ultimately alleviate AD-related neuroinflammation.

Novel Psychoactive Substances: The Razor's Edge between Therapeutical Potential and Psychoactive Recreational Misuse

BACKGROUND

Novel psychoactive substances (NPS) are compounds of natural and synthetic origin, similar to traditional drugs of abuse. NPS are involved in a contemporary trend whose origin lies in a thinner balance between legitimate therapeutic drug research and legislative control. The contemporary NPS trend resulted from the replacement of MDMA by synthetic cathinones in 'ecstasy' during the 2000s. The most common NPS are synthetic cannabinoids and synthetic cathinones. Interestingly, during the last 50 years, these two classes of NPS have been the object of scientific research for a set of health conditions.

METHODS

Searches were conducted in the online database PubMed using boolean equations.

RESULTS

Synthetic cannabinoids displayed protective and therapeutic effects for inflammatory, neurodegenerative and oncologic pathologies, activating the immune system and reducing inflammation. Synthetic cathinones act similarly to amphetamine-type stimulants and can be used for depression and chronic fatigue.

CONCLUSIONS

Despite the scientific advances in this field of research, pharmacological application of NPS is being jeopardized by fatalities associated with their recreational use. This review addresses the scientific achievements of these two classes of NPS and the toxicological data, ending with a reflection on Illicit and NPS control frames.

Ginsenoside compound K acts via LRP1 to alleviate Amyloid β42-induced neuroinflammation in microglia by suppressing NF-κB

BACKGROUND

Alzheimer's disease (AD), has caused a mass of disability and mortality in elder populations, which increases global health burden. There are still limited effective disease-modifying drugs. Alleviating microglia-evoked neuroinflammation has become a promising treatment strategy for AD. Ginsenoside Compound K has been demonstrated to exhibit anti-inflammatory and neuroprotective benefits. Here we measured the effects of Ginsenoside Compound K in inhibiting amyloid-induced microglia inflammation and the possible molecular mechanisms and target of action in vitro.

METHODS

The cytotoxicity of all chemical reagents on BV2 cells were evaluated using the MTT assay. qRT-PCR and ELISA were carried out to detect the inflammatory cytokines levels. Western blot was utilized to determine the effect of Ginsenoside Compound K on the nuclear factor-κB (NF-κB) p65 nuclear translocation. Antagonist Receptor Associated Protein (RAP) was used to verify the engagement of low-density lipoprotein receptor-related protein 1(LRP1).

RESULTS

Ginsenoside Compound K diminished inflammatory cytokine production and reversed NF-κB p65 nuclear translocation induced by Aβ₄₂ oligomers. LRP1 expression was up-regulated by Ginsenoside Compound K. When LRP1 was blocked by antagonist RAP, the protective effect of Ginsenoside Compound K was massively eliminated.

CONCLUSION

These observations provide evidence for anti-inflammatory effect of Ginsenoside Compound K through NF-κB pathway via LRP1 activation, and support further evaluation of Ginsenoside Compound K as a potential effective modulator for AD.

A Revisit to Etiopathogenesis and Therapeutic Strategies in Alzheimer's Disease

Dementia is a cluster of brain abnormalities that trigger progressive memory deficits and other cognitive abilities such as skills, language, or executive function. Alzheimer's disease (AD) is the foremost type of age-associated dementia that involves progressive neurodegeneration accompanied by profound cognitive deficits in advanced stages that severely hamper social or occupational abilities with or without the involvement of any other psychiatric condition. The last two decades witnessed a sharp increase (~123%) in mortality due to AD type dementia, typically owing to a very low disclosure rate (~45%) and hence, the prophylactic, as well as the therapeutic cure of AD, has been a huge challenge. Although understanding of AD pathogenesis has witnessed a remarkable growth (e.g., tauopathy, oxidative stress, lipid transport, glucose uptake, apoptosis, synaptic dysfunction, inflammation, and immune system), still a dearth of an effective therapeutic agent in the management of AD prompts the quest for newer pharmacological targets in the purview of its growing epidemiological status. Most of the current therapeutic strategies focus on modulation of a single target, e.g., inhibition of acetylcholinesterase, glutamate excitotoxicity (memantine), or nootropics (piracetam), even though AD is a multifaceted neurological disorder. There is an impedance urgency to find not only symptomatic but effective disease-modifying therapies. The present review focuses on the risk / protective factors and pathogenic mechanisms involved in AD. In addition to the existing symptomatic therapeutic approach, a diverse array of possible targets linked to pathogenic cascades have been re-investigated to envisage the pharmacotherapeutic strategies in AD.

The Beneficial Role of Exercise on Treating Alzheimer's Disease by Inhibiting β-Amyloid Peptide

Alzheimer's disease (AD) is associated with a very large burden on global healthcare systems. Thus, it is imperative to find effective treatments of the disease. One feature of AD is the accumulation of neurotoxic β-amyloid peptide (Aβ). Aβ induces multiple pathological processes that are deleterious to nerve cells. Despite the development of medications that target the reduction of Aβ to treat AD, none has proven to be effective to date. Non-pharmacological interventions, such as physical exercise, are also being studied. The benefits of exercise on AD are widely recognized. Experimental and clinical studies have been performed to verify the role that exercise plays in reducing Aβ deposition to alleviate AD. This paper reviewed the various mechanisms involved in the exercise-induced reduction of Aβ, including the regulation of amyloid precursor protein cleaved proteases, the glymphatic system, brain-blood transport proteins, degrading enzymes and autophagy, which is beneficial to promote exercise therapy as a means of prevention and treatment of AD and indicates that exercise may provide new therapeutic targets for the treatment of AD.

Genetic Variants Associated With Alzheimer Disease in the 22 Arab Countries: A Systematic Review

BACKGROUND AND AIMS

Alzheimer disease (AD) is a progressive and complex neurodegenerative disease. Approximately 70% of AD risk is attributed to genetic risk factors, including variants in amyloid precursor protein (APP), presenilin 1 (PSEN1), and presenilin 2 (PSEN2) genes. Several studies have revealed a considerable number of candidate loci and genes for AD among different ethnic populations. However, the outcomes of these studies have been inconsistent. In this study, we aimed to investigate the spectrum of variants that are associated with the onset and development of AD among 22 Arab countries.

METHODOLOGY

We systematically searched 4 literature databases (Science Direct, Scopus, PubMed, and Web of Science) from the date of inception until July 2020 using various search terms to obtain all the reported genetic data on Arab AD cases.

RESULTS

In total, 18 studies were included, comprising a total of 2173 individuals, of whom 888 were clinically diagnosed AD patients and were genetically tested for genes and variants associated with AD. A total of 27 variants in 8 genes were found to be associated with AD. Of these variants, 17 were unique to the Arab population and 10 were shared with other ethnic groups.

CONCLUSIONS

There is a dearth of studies on the genetics of AD in the Arab world. There seems to be distinctive genetic and clinical susceptibility profiles for Arab patients with AD.

Review of the Protective Effects of Statins on Cognition

Elevated cholesterol is a major risk factor in the development of cardiovascular disease. Statins have proven to be effective in lowering low-density lipoprotein cholesterol as well as the incidence of cardiovascular events. As a result, statins are widely prescribed in the United States, with an estimated 35 million patients on statins. Many of these patients are older than age 65 and suffer from various comorbidities, including mild to severe cognitive impairment. Early studies looking at the effects of statins on cognition have shown that statin use may lead to mild reversible cognitive decline, although long-term studies have shown inconclusive findings. In recent years, studies have shown that the use of statins in certain groups of patients may lead to a reduction in the rate of cognitive decline. One hypothesis for this finding is that statin use can reduce the risk of cerebrovascular disease which may, in turn, reduce the risk of mild cognitive decline and dementia. With numerous patients currently prescribed statins and the likelihood that more patients will be prescribed the medication in the coming years, it is important to review the current literature to determine the association between statin use and cognitive decline, as well as determine how statins may be beneficial in preventing cognitive decline.

Chronic Periodontitis and Alzheimer Disease: A Putative Link of Serum Proteins Identification by 2D-DIGE Proteomics

Increasing evidence indicates Chronic Periodontitis (CP) is a comorbidity of Alzheimer’s disease (AD), which is the most common form of age-related dementia, and for the latter, effective diagnostic and treatment strategies are lacking. Although inflammation is present in both diseases, the exact mechanisms and cross-links between CP and AD are poorly understood; and a direct association between the two has not been reported. This study aimed to identify a direct serum proteins link between AD and CP. Two-dimensional differential in-gel electrophoresis was employed to analyze serum samples from 12 CP patients and 12 age-matched controls. Furthermore, to determine the molecular link between CP and AD, neuroblastoma SK-N-SH APPwt cells were treated with 1 μg/ml of lipopolysaccharide from Porphyromonas gingivalis (P.g-LPS). Ten differentially expressed proteins were identified in CP patients. Among them, nine proteins were up-regulated, and one protein was down-regulated. Of the 10 differentially expressed proteins, five proteins were reportedly involved in the pathology of AD: Cofilin-2, Cathepsin B, Clusterin, Triosephosphate isomerase, and inter-alpha-trypsin inhibitor heavy chain H4 (ITI-H4). Western blotting indicated significantly higher expression of Cofilin-2, Cathepsin B, and Clusterin and lower expression of ITI-H4 in the CP group than in the Control group. The serum concentration of Cathepsin B has a good correlation with MMSE scores. Moreover, the protein level of Cathepsin B (but not that of ADAM10 and BACE1) increased significantly along with a prominent increase in Aβ_1–40 and Aβ_1–42 in the cell lysates of P.g-LPS-treated SK-N-SH APPwt cells. Cathepsin B inhibition resulted in a sharp decrease in Aβ_1–40 and Aβ_1–42 in the cell lysates. Furthermore, TNF-α was one of the most important inflammatory cytokines for the P.g-LPS-induced Cathepsin B upregulation in SK-N-SH APPwt cells. These results show that CP and AD share an association, while Cathepsin B could be a key link between the two diseases. The discovery of the identical serum proteins provides a potential mechanism underlying the increased risk of AD in CP patients, which could be critical for elucidating the pathophysiology of AD.

Statin therapy: does sex matter?

OBJECTIVE

Statins are a class of drugs that competitively bind to the active site of HMG-CoA reductase enzyme, thereby inhibiting the initial steps in cholesterol synthesis. Originally approved for use in lowering serum cholesterol, a risk factor for developing atherosclerosis and coronary heart disease, statins have subsequently been noted to have myriad extrahepatic effects, including potential effects on cognition, diabetes, breast cancer, bone, and muscle. This narrative review assesses the current state of the science regarding the risks and benefits of statin therapy in women to identify areas where additional research is needed.

METHODS

Basic and clinical studies were identified by searching PubMed with particular attention to inclusion of female animals, women, randomized controlled trials, and sex-specific analyses.

RESULTS

Statin therapy is generally recommended to reduce the risk of cardiovascular disease. None of the current clinical guidelines, however, offer sex-specific recommendations for women due to lack of understanding of sex differences and underlying mechanisms of disease processes. In addition, conclusions regarding efficacy of treatments do not consider lipid solubility for the drug, dosing, duration of treatment, interactions with estrogen, or comorbidities. Pleiotropic effects of statins are often derived from secondary analysis of studies with cardiovascular events as primary outcomes.

CONCLUSIONS

Many of the trials that have established the efficacy and safety of statins were conducted predominantly or entirely in men, with results extrapolated to women. Additional research is needed to guide clinical recommendations specific to women. : Video Summary:http://links.lww.com/MENO/A462.

Therapeutic Potential of Direct Clearance of the Amyloid-β in Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by deposition and accumulation of amyloid-β (Aβ) and its corresponding plaques within the brain. Although much debate exists whether these plaques are the cause or the effect of AD, the accumulation of Aβ is linked with the imbalance between the production and clearance of Aβ. The receptor for advanced glycation endproducts (RAGE) facilitates entry of free Aβ from the peripheral stream. Conversely, lipoprotein receptor-related protein 1 (LRP1), located in the abluminal side at the blood–brain barrier mediates the efflux of Aβ. Research on altering the rates of clearance of Aβ by targeting these two pathways has been extensively study. Additionally, a cerebrospinal fluid (CSF) circulation assistant device has also been evaluated as an approach to increase solute concentration in the CSF via mechanical drainage, to allow for removal of Aβ from the brain. Herein, we provide a brief review of these approaches that are designed to re-establish a homeostatic Aβ balance in the brain.

Alzheimer's disease: risk factors and potentially protective measures

Alzheimer's disease (AD) is the most common type of dementia and typically manifests through a progressive loss of episodic memory and cognitive function, subsequently causing language and visuospatial skills deficiencies, which are often accompanied by behavioral disorders such as apathy, aggressiveness and depression. The presence of extracellular plaques of insoluble β-amyloid peptide (Aβ) and neurofibrillary tangles (NFT) containing hyperphosphorylated tau protein (P-tau) in the neuronal cytoplasm is a remarkable pathophysiological cause in patients' brains. Approximately 70% of the risk of developing AD can be attributed to genetics. However, acquired factors such as cerebrovascular diseases, diabetes, hypertension, obesity and dyslipidemia increase the risk of AD development. The aim of the present minireview was to summarize the pathophysiological mechanism and the main risk factors for AD. As a complement, some protective factors associated with a lower risk of disease incidence, such as cognitive reserve, physical activity and diet will also be addressed.

Development of AD-Like Pathology in Skeletal Muscle

Effective therapeutic strategy against Alzheimer's disease (AD) requires early detection of AD; however, clinical diagnosis of Alzheimer's disease (AD) is not precise and a definitive diagnosis of AD is only possible via postmortem examination for AD pathological hallmarks including senile plaques composed of Aβ and neuro fibrillary tangles composed of phosphorylated tau. Although a variety of biomarker has been developed and used in clinical setting, none of them robustly predicts subsequent clinical course of AD. Thus, it is essential to identify new biomarkers that may facilitate the diagnosis of early stages of AD, prediction of subsequent clinical course, and development of new therapeutic strategies. Given that pathological hallmarks of AD including Aβaccumulation and the presence of phosphorylated tau are also detected in peripheral tissues, AD is considered a systemic disease. Without the protection of blood-brain barrier, systemic factors can affect peripheral tissues much earlier than neurons in brain. Here, we will discuss the development of AD-like pathology in skeletal muscle and the potential use of skeletal muscle biopsy (examination for Aβaccumulation and phosphorylated tau) as a biomarker for AD.

Leaky brain in neurological and psychiatric disorders: Drivers and consequences

BACKGROUND

The blood-brain barrier acts as a highly regulated interface; its dysfunction may exacerbate, and perhaps initiate, neurological and neuropsychiatric disorders.

METHODS

In this narrative review, focussing on redox, inflammatory and mitochondrial pathways and their effects on the blood-brain barrier, a model is proposed detailing mechanisms which might explain how increases in blood-brain barrier permeability occur and can be maintained with increasing inflammatory and oxidative and nitrosative stress being the initial drivers.

RESULTS

Peripheral inflammation, which is causatively implicated in the pathogenesis of major psychiatric disorders, is associated with elevated peripheral pro-inflammatory cytokines, which in turn cause increased blood-brain barrier permeability. Reactive oxygen species, such as superoxide radicals and hydrogen peroxide, and reactive nitrogen species, such as nitric oxide and peroxynitrite, play essential roles in normal brain capillary endothelial cell functioning; however, chronically elevated oxidative and nitrosative stress can lead to mitochondrial dysfunction and damage to the blood-brain barrier. Activated microglia, redox control of which is mediated by nitric oxide synthases and nicotinamide adenine dinucleotide phosphate (NADPH) oxidases, secrete neurotoxic molecules such as reactive oxygen species, nitric oxide, prostaglandin, cyclooxygenase-2, quinolinic acid, several chemokines (including monocyte chemoattractant protein-1 [MCP-1], C-X-C motif chemokine ligand 1 [CXCL-1] and macrophage inflammatory protein 1α [MIP-1α]) and the pro-inflammatory cytokines interleukin-6, tumour necrosis factor-α and interleukin-1β, which can exert a detrimental effect on blood-brain barrier integrity and function. Similarly, reactive astrocytes produce neurotoxic molecules such as prostaglandin E2 and pro-inflammatory cytokines, which can cause a 'leaky brain'.

CONCLUSION

Chronic inflammatory and oxidative and nitrosative stress is associated with the development of a 'leaky gut'. The following evidence-based approaches, which address the leaky gut and blood-brain barrier dysfunction, are suggested as potential therapeutic interventions for neurological and neuropsychiatric disorders: melatonin, statins, probiotics containing Bifidobacteria and Lactobacilli, N-acetylcysteine, and prebiotics containing fructo-oligosaccharides and galacto-oligosaccharides.

Neuroprotective effects of statins against amyloid β-induced neurotoxicity

A growing body of evidence suggests that disruption of the homeostasis of lipid metabolism affects the pathogenesis of Alzheimer's disease (AD). In particular, dysregulation of cholesterol homeostasis in the brain has been reported to considerably increase the risk of developing AD. Thus, dysregulation of lipid homeostasis may increase the amyloid β (Aβ) levels by affecting amyloid precursor protein (APP) cleavage, which is the most important risk factor involved in the pathogenesis of AD. Previous research demonstrated that Aβ can trigger neuronal insulin resistance, which plays an important role in response to Aβ-induced neurotoxicity in AD. Epidemiological studies also suggested that statin use is associated with a decreased incidence of AD. Therefore, statins are believed to be a good candidate for conferring neuroprotective effects against AD. Statins may play a beneficial role in reducing Aβ-induced neurotoxicity. Their effect involves a putative mechanism beyond its cholesterol-lowering effects in preventing Aβ-induced neurotoxicity. However, the underlying molecular mechanisms of the protective effect of statins have not been clearly determined in Aβ-induced neurotoxicity. Given that statins may provide benefits beyond the inhibition of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, these drugs may also improve the brain. Thus, statins may have beneficial effects on impaired insulin signaling by activating AMP-activated protein kinase (AMPK) in neuronal cells. They play a potential therapeutic role in targeting Aβ-mediated neurotoxicity.

Statins and Brain Health: Alzheimer's Disease and Cerebrovascular Disease Biomarkers in Older Adults

BACKGROUND

Statins have been proposed to reduce the risk of Alzheimer's disease (AD).

OBJECTIVE

Assess whether long-term statin use was associated with neuroimaging biomarkers of aging and dementia.

METHODS

Methods: We analyzed neuroimaging biomarkers in 1,160 individuals aged 65+ from the Mayo Clinic Study of Aging, a population-based prospective longitudinal study of cognitive aging.

RESULTS

Statin-treated (5+ years of therapy) individuals had greater burden of mid-and late-life cardiovascular disease (p < 0.001) than statin-untreated (≤3 months) individuals. Lower fractional anisotropy in the genu of the corpus callosum, an early marker of cerebrovascular disease, was associated with long-term statin exposure (p < 0.035). No significant associations were identified between long-term statin exposure and cerebral amyloid or tau burden, AD pattern neurodegeneration, or white matter hyperintensity burden.

CONCLUSIONS

Long-term statin therapy was not associated with differences in AD biomarkers. Individuals with long-term statin exposure had worse white matter integrity in the genu of the corpus callosum, consistent with the coexistence of higher cerebrovascular risk factor burden in this group.

Role of LRP1 in the pathogenesis of Alzheimer's disease: evidence from clinical and preclinical studies

Among the LDL receptor (LDLR) family members, the roles of LDLR-related protein (LRP)1 in the pathogenesis of Alzheimer's disease (AD), especially late-onset AD, have been the most studied by genetic, neuropathological, and biomarker analyses (clinical studies) or cellular and animal model systems (preclinical studies) over the last 25 years. Although there are some conflicting reports, accumulating evidence from preclinical studies indicates that LRP1 not only regulates the metabolism of amyloid-β peptides (Aβs) in the brain and periphery, but also maintains brain homeostasis, impairment of which likely contributes to AD development in Aβ-independent manners. Several preclinical studies have also demonstrated an involvement of LRP1 in regulating the pathogenic role of apoE, whose gene is the strongest genetic risk factor for AD. Nonetheless, evidence from clinical studies is not sufficient to conclude how LRP1 contributes to AD development. Thus, despite very promising results from preclinical studies, the role of LRP1 in AD pathogenesis remains to be further clarified. In this review, we discuss the potential mechanisms underlying how LRP1 affects AD pathogenesis through Aβ-dependent and -independent pathways by reviewing both clinical and preclinical studies. We also discuss potential therapeutic strategies for AD by targeting LRP1.

APP Function and Lipids: A Bidirectional Link

Extracellular neuritic plaques, composed of aggregated amyloid-β (Aβ) peptides, are one of the major histopathological hallmarks of Alzheimer's disease (AD), a progressive, irreversible neurodegenerative disorder and the most common cause of dementia in the elderly. One of the most prominent risk factor for sporadic AD, carrying one or two aberrant copies of the apolipoprotein E (ApoE) ε4 alleles, closely links AD to lipids. Further, several lipid classes and fatty acids have been reported to be changed in the brain of AD-affected individuals. Interestingly, the observed lipid changes in the brain seem not only to be a consequence of the disease but also modulate Aβ generation. In line with these observations, protective lipids being able to decrease Aβ generation and also potential negative lipids in respect to AD were identified. Mechanistically, Aβ peptides are generated by sequential proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretase. The α-secretase appears to compete with β-secretase for the initial cleavage of APP, preventing Aβ production. All APP-cleaving secretases as well as APP are transmembrane proteins, further illustrating the impact of lipids on Aβ generation. Beside the pathological impact of Aβ, accumulating evidence suggests that Aβ and the APP intracellular domain (AICD) play an important role in regulating lipid homeostasis, either by direct effects or by affecting gene expression or protein stability of enzymes involved in the de novo synthesis of different lipid classes. This review summarizes the current literature addressing the complex bidirectional link between lipids and AD and APP processing including lipid alterations found in AD post mortem brains, lipids that alter APP processing and the physiological functions of Aβ and AICD in the regulation of several lipid metabolism pathways.

Effects of vascular risk factors, statins, and antihypertensive drugs on PiB deposition in cognitively normal subjects

INTRODUCTION

Hypertension, hypercholesterolemia, and obesity increase the risk of dementia. Although their detection is commonly followed by an introduction of treatment, little is known about how medications frequently used to treat vascular risk affect amyloid deposition.

METHODS

A cross-sectional study of 156 subjects who underwent positron emission tomography with PiB. Using linear regression, we tested whether blood pressure, cholesterol, overweight/obese status, angiotensin receptor blockers (ARBs), beta-blockers, diuretics, angiotensin converting enzyme inhibitors, and statins predicted amyloid deposition.

RESULTS

The use of ARBs (β = -.15, P = .044) and diuretics (β = -.20, P = .006) predicted less amyloid accumulation; older age (β = .29, P < .001) and statins (β = .23, P = .004) were related to greater amyloid deposition. Overweight and/or obese women had more cortical amyloid than their peers.

DISCUSSION

Prospective studies should confirm effects of drugs and increased body weight on amyloid accumulation and establish whether they translate into measurable clinical outcomes. Women may be more susceptible to harmful effects of obesity.

The Role of Amyloid-β Oligomers in Toxicity, Propagation, and Immunotherapy

The incidence of Alzheimer's disease (AD) is growing every day and finding an effective treatment is becoming more vital. Amyloid-β (Aβ) has been the focus of research for several decades. The recent shift in the Aβ cascade hypothesis from all Aβ to small soluble oligomeric intermediates is directing the search for therapeutics towards the toxic mediators of the disease. Targeting the most toxic oligomers may prove to be an effective treatment by preventing their spread. Specific targeting of oligomers has been shown to protect cognition in rodent models. Additionally, the heterogeneity of research on Aβ oligomers may seem contradictory until size and conformation are taken into account. In this review, we will discuss Aβ oligomers and their toxicity in relation to size and conformation as well as their influence on inflammation and the potential of Aβ oligomer immunotherapy.

APOE2 eases cognitive decline during Aging: Clinical and preclinical evaluations

OBJECTIVE

Apolipoprotein E (apoE), a major cholesterol carrier in the brain, is associated with a strong risk for Alzheimer disease. Compared to the risky APOE4 gene allele, the effects of the protective APOE2 gene allele are vastly understudied, and thus need to be further clarified.

METHODS

We reviewed National Alzheimer's Coordinating Center clinical records and performed preclinical experiments using human apoE-targeted replacement (apoE-TR) mice, which do not show amyloid pathology.

RESULTS

Clinically, the APOE2 allele was associated with less cognitive decline during aging. This effect was also seen in subjects with little amyloid pathology, or after adjusting for Alzheimer disease-related pathologies. In animal studies, aged apoE2-TR mice also exhibited preserved memory function in water maze tests. Regardless, apoE2-TR mice showed similar or greater age-related changes in synaptic loss, neuroinflammation, and oxidative stress compared to apoE3-TR or apoE4-TR mice. Interestingly, apoE concentrations in the cortex, hippocampus, plasma, and cerebrospinal fluid (CSF) were positively correlated with memory performance across apoE isoforms, where apoE2-TR mice had higher apoE levels. Moreover, apoE2-TR mice exhibited the lowest levels of cholesterol in the cortex, despite higher levels in CSF and plasma. These cholesterol levels were associated with apoE levels and memory performance across apoE isoforms.

INTERPRETATION

APOE2 is associated with less cognitive decline during aging. This can occur independently of age-related synaptic/neuroinflammatory changes and amyloid accumulation. Higher levels of apoE and associated cholesterol metabolism in APOE2 carriers might contribute to this protective effect. Ann Neurol 2016;79:758-774.

An overview on therapeutics attenuating amyloid β level in Alzheimer's disease: targeting neurotransmission, inflammation, oxidative stress and enhanced cholesterol levels

Alzheimer's disease (AD) is the most common underlying cause of dementia, and novel drugs for its treatment are needed. Of the different theories explaining the development and progression of AD, "amyloid hypothesis" is the most supported by experimental data. This hypothesis states that the cleavage of amyloid precursor protein (APP) leads to the formation of amyloid beta (Aβ) peptides that congregate with formation and deposition of Aβ plaques in the frontal cortex and hippocampus. Risk factors including neurotransmitter modulation, chronic inflammation, metal-induced oxidative stress and elevated cholesterol levels are key contributors to the disease progress. Current therapeutic strategies abating AD progression are primarily based on anti-acetylcholinesterase (AChE) inhibitors as cognitive enhancers. The AChE inhibitor, donepezil, is proven to strengthen cognitive functions and appears effective in treating moderate to severe AD patients. N-Methyl-D-aspartate receptor antagonist, memantine, is also useful, and its combination with donepezil demonstrated a strong stabilizing effect in clinical studies on AD. Nonsteroidal anti-inflammatory drugs delayed the onset and progression of AD and attenuated cognitive dysfunction. Based upon epidemiological evidence and animal studies, antioxidants emerged as potential AD preventive agents; however, clinical trials revealed inconsistencies. Pharmacokinetic and pharmacodynamic profiling demonstrated pleiotropic functions of the hypolipidemic class of drugs, statins, potentially contributing towards the prevention of AD. In addition, targeting the APP processing pathways, stimulating neuroprotective signaling mechanisms, using the amyloid anti-aggregants and Aβ immunotherapy surfaced as well-tested strategies in reducing the AD-like pathology. Overall, this review covers mechanism of inducing the Aβ formation, key risk factors and major therapeutics prevalent in the AD treatment nowadays. It also delineates the need for novel screening approaches towards identifying drugs that may prevent or at least limit the progression of this devastating disease.

The roles of lipid and glucose metabolism in modulation of β-amyloid, tau, and neurodegeneration in the pathogenesis of Alzheimer disease

Diabetes is a risk factor for Alzheimer disease (AD). Apolipoprotein E (ApoE) and several genes related to AD have recently been identified by genome-wide association studies (GWAS) as being closely linked to lipid metabolism. Lipid metabolism and glucose-energy metabolism are closely related. Here, we review the emerging evidence regarding the roles of lipid and glucose metabolism in the modulation of β-amyloid, tau, and neurodegeneration during the pathogenesis of AD. Disruption of homeostasis of lipid and glucose metabolism affects production and clearance of β-amyloid and tau phosphorylation, and induces neurodegeneration. A more integrated understanding of the interactions among lipid, glucose, and protein metabolism is required to elucidate the pathogenesis of AD and to develop next-generation therapeutic options.

Role of endolysosomes and cholesterol in the pathogenesis of Alzheimer's disease: Insights into why statins might not provide clinical benefit

Altered cholesterol homeostasis in general and increased levels of low-density lipoprotein (LDL) cholesterol specifically is a robust risk factor for the pathogenesis of sporadic Alzheimer's disease (AD). Because of this, the family of drugs known as statins have been tried extensively to lower cholesterol levels in attempting to prevent and/or lessen the neuropathogenesis of AD. Unfortunately, evidence accumulated to date is insufficient to support the continued use of statins as a viable pharmacotherapeutic approach against AD. To understand these complex and inter-related issues it is important to review how altered cholesterol homeostasis contributes to AD pathogenesis and why statins have not provided clinical benefit against AD. Apolipoproteins with their different affinities for various lipids and the receptors that control cholesterol uptake can result in drastic differences in cholesterol trafficking into and its distribution within neurons. The presence of the apoE4 or elevated plasma levels of LDL cholesterol can lead to a set of conditions that resembles lysosomal lipid storage disorders observed in Niemann-Pick type C disease such as impaired recycling of cholesterol back to the endoplasmic reticulum (ER), Golgi and plasma membranes, cholesterol deficiencies in plasma membranes, and increased cholesterol accumulation in endolysosomes resulting in endolysosome dysfunction. Consequently, the use of statins to block cholesterol synthesis in ER might not only decrease further plasma membrane cholesterol levels thus disturbing synaptic integrity, but also could also increase cholesterol burden in endolysosomes thus worsening endolysosome dysfunction. Therefore, it is not surprising that the use of cholesterol-lowering strategies with statins has not resulted in clinical benefit for patients living with AD.

Successful therapies for Alzheimer's disease: why so many in animal models and none in humans?

Peering into the field of Alzheimer’s disease (AD), the outsider realizes that many of the therapeutic strategies tested (in animal models) have been successful. One also may notice that there is a deficit in translational research, i.e., to take a successful drug in mice and translate it to the patient. Efforts are still focused on novel projects to expand the therapeutic arsenal to “cure mice.” Scientific reasons behind so many successful strategies are not obvious. This article aims to review the current approaches to combat AD and to open a debate on common mechanisms of cognitive enhancement and neuroprotection. In short, either the rodent models are not good and should be discontinued, or we should extract the most useful information from those models. An example of a question that may be debated for the advancement in AD therapy is: In addition to reducing amyloid and tau pathologies, would it be necessary to boost synaptic strength and cognition? The debate could provide clues to turn around the current negative output in generating effective drugs for patients. Furthermore, discovery of biomarkers in human body fluids, and a clear distinction between cognitive enhancers and disease modifying strategies, should be instrumental for advancing in anti-AD drug discovery.

Altered Cholesterol Intracellular Trafficking and the Development of Pathological Hallmarks of Sporadic AD

Compared to the rare familial early onset Alzheimer's disease (AD) that results from gene mutations in AbPP and presenilin-1, the pathogenesis of sporadic AD is much more complex and is believed to result from complex interactions between nutritional, environmental, epigenetic and genetic factors. Among those factors, the presence APOE4 is still the single strongest genetic risk factor for sporadic AD. However, the exact underlying mechanism whereby apoE4 contributes to the pathogenesis of sporadic AD remains unclear. Here, we discuss how altered cholesterol intracellular trafficking as a result of apoE4 might contribute to the development of pathological hallmarks of AD including brain deposition of amyloid beta (Ab), neurofibrillary tangles, and synaptic dysfunction.

Role of LDL cholesterol and endolysosomes in amyloidogenesis and Alzheimer's disease

The pathogenesis of late-onset sporadic Alzheimer's disease (AD) is believed to result from complex interactions between nutritional, environmental, epigenetic and genetic factors. Among those factors, altered circulating cholesterol homeostasis, independent of the APOE genotype, continues to be implicated in brain deposition of amyloid beta protein (Aβ) and the pathogenesis of AD. It is believed that trafficking of amyloid beta precursor protein (AβPP) into endolysosomes appears to play a critical role in determining amyloidogenic processing of AβPP because this is precisely where two enzymes critically important in AβPP metabolism are located; beta amyloid converting enzyme (BACE-1) and gamma secretase enzyme. We have shown that elevated levels of LDL cholesterol promote AβPP internalization, disturb neuronal endolysosome structure and function, and increase Aβ accumulation in neuronal endolysosomes. Here, we will further discuss the linkage between elevated levels of LDL cholesterol and AD pathogenesis, and explore the underlying mechanisms whereby elevated levels of plasma LDL cholesterol promote amyloidogenesis.