Emerging roles for high-density lipoproteins in neurodegenerative disorders

Identification and mechanism analysis of biomarkers related to butyrate metabolism in COVID-19 patients

BACKGROUND

Butyrate may inhibit SARS-CoV-2 replication and affect the development of COVID-19. However, there have been no systematic comprehensive analyses of the role of butyrate metabolism-related genes (BMRGs) in COVID-19.

METHODS

We performed differential expression analysis of BMRGs in the brain, liver and pancreas of COVID-19 patients and controls in GSE157852 and GSE151803. The differentially expressed genes (DEGs) and module genes between COVID-19 patients and healthy controls in GSE171110 were screened through 'limma' and 'WGANA' R package, respectively, followed by an intersection with BMRGs via 'ggvenn' R package. Six machine learning algorithms were employed to determine the best model for identifying biomarkers, and receiver operating characteristic (ROC) curves were plotted to evaluate the diagnostic value of the biomarkers in COVID-19. Moreover, the differences in immune-infiltrating cells between the COVID-19 and control groups were compared using CIBERSORT. The differences in immune cells and expression levels of biomarkers in immune cells among different tissues were analysed using GSE171668.

RESULTS

The BMRGs were the most different in the brain between the COVID-19 and control groups, including 21 upregulated and 16 downregulated genes. Five important common BMRGs were screened as biomarkers for COVID-19 using XGBoost, namely CCNB1, CCNA2, BRCA1, HBB and HSPA5, with increased diagnostic performance. Enrichment analysis revealed that these five genes were related to the cell cycle, cell proliferation and cell senescence. The infiltrating abundance of 12 immune cells was different between the COVID-19 and control groups. Finally, the expression levels of HSPA5, BRCA1 and HBB were higher in annotated cells than in CCNB1 and CCNA2, and there were four different types of immune cells in the liver, heart, lungs and kidneys.

CONCLUSIONS

These five genes may be potential biomarkers of butyrate metabolism in COVID-19 patients. These findings provide a direction for further studies on the molecular mechanisms underlying COVID-19.

Plasma and urinary metabolomic signatures differentiate genetic and idiopathic Parkinson's disease

Parkinson's disease (PD) is marked by alpha-synuclein accumulation and progressive dopaminergic neuron loss. Using Nuclear Magnetic Resonance (NMR)-based metabolomics, we uncovered metabolic disturbances in idiopathic PD (iPD) and PD linked to LRRK2, GBA1, and PRKN variants in a Brazilian ethnically diverse cohort, free of comorbidities, in comparison to healthy, age-matched controls. In plasma, significant PD-associated metabolites included histidine, acetate, acetoacetate, glutamine, glucose, lipids and lipoproteins, N-acetyl-glycoproteins, and sarcosine. Urine samples revealed alterations in creatine, creatinine, L-asparagine, trimethylamine, 3-beta-hydroxybutyrate, isovaleric acid, glutamine, urea, glycine, choline, arginine, and cysteine in association with PD. Notably, creatine, creatinine, acetate, glucose, and histidine showed pathway influences from LRRK2, GBA1, and PRKN variants. Enrichment analyses highlighted disruptions in glyoxylate and dicarboxylate metabolism (plasma) as well as serine, threonine, and glycine metabolism (urine). Additionally, a metabolite-gene-disease interaction network identified 15 genes associated with PD that interact with key metabolites, highlighting MAPT, SNCA, RERE, and KCNN3 as key players in both plasmaandurine. NMR in saliva samples did not show significant differences between PD groups and controls. Our findings underscore PD-associated metabolites, particularly related to arginine metabolism, the urea cycle, glutamate metabolism, glucose metabolism, and gut microbiota. These pathways and gene interactions may serve as potential biomarkers for PD diagnosis and precision medicine strategies.

Cholesterol-modifying strategies for Alzheimer disease: promise or fallacy?

INTRODUCTION

As the world population ages, Alzheimer disease (AD) prevalence increases. However, understanding of AD etiology continues to evolve, and the pathophysiological processes involved are only partially elucidated. One compound suspected to play a role in the development and progression of AD is cholesterol. Several lines of evidence support this connection, yet it remains unclear whether cholesterol-modifying strategies have potential applications in the clinical management of AD.

AREAS COVERED

A deep literature search using PubMed was performed to prepare this narrative review. The literature search, performed in early 2024, was inclusive of literature from 1990 to 2024. After providing an overview of cholesterol metabolism, this study summarizes key preclinical studies that have investigated cholesterol-modifying therapies in laboratory models of AD. It also summarizes past and current clinical trials testing specific targets modulated by anti-cholesterol therapies in AD patients.

EXPERT OPINION

Based on current epidemiological and mechanistic studies, cholesterol likely plays a role in AD etiology. The use of cholesterol-modifying therapies could be a promising treatment approach if administered at presymptomatic to early AD phases, but it is unlikely to be efficient in mild, moderate, and late AD stages. Several recommendations are provided for hypercholesterolemia management in AD patients.

The Association of Wnt Signaling Pathway Gene Variants, Blood Lipoproteins and Cognitive Function in Elderly People

Wnt signaling is believed to play an important role in the nervous system. However, few studies have examined the association between gene variants of the Wnt signaling pathway and mild cognitive impairment (MCI). Additionally, the potential modulation of this association by blood lipoproteins remains poorly understood. We aimed to investigate these associations in the present analysis. The cross-sectional study comprised 459 participants from 17 villages in Jimo District, Qingdao, Shandong Province. A total of 46 single nucleotide polymorphisms (SNPs) in nine Wnt signaling pathway genes were included. Cognitive function was measured using Montreal Cognitive Assessment (MOCA). Polygenic risk scores (PRS) were used to summarize the effect of each gene. Ordered logistic regression and Poisson regression with robust variance were applied to examine the associations of SNPs with MCI and the dimension score of MOCA. Interaction analysis was conducted to verify the interaction with lipoproteins. A random forest classifier was used to develop a predictive model for MCI. The SNP PRKCA-rs2286674 was associated with MCI across three models. The risk of MCI increased by 31% and 2% for each unit increase of PRS of PRKCA and WNT7B respectively. Based on the multiplicative interaction model, the effects of certain PRSs on the risk of MCI were modified by blood lipoproteins. Integrating total PRS into the prediction model significantly improved the ability to predict MCI. Genetic variations in Wnt signaling pathway were associated with MCI in older adults. Interaction effects between gene variants and blood lipoproteins on MCI were observed.

Nanosystems for targeted drug Delivery: Innovations and challenges in overcoming the Blood-Brain barrier for neurodegenerative disease and cancer therapy

The evolution of sophisticated nanosystems has revolutionized biomedicine, notably in treating neurodegenerative diseases and cancer. These systems show potential in delivering medication precisely to affected tissues, improving treatment effectiveness while minimizing side effects. Nevertheless, a major hurdle in targeted drug delivery is breaching the blood-brain barrier (BBB), a selective shield separating the bloodstream from the brain and spinal cord. The tight junctions between endothelial cells in brain capillaries create a formidable physical barrier, alongside efflux transporters that expel harmful molecules. This presents a notable challenge for brain drug delivery. Nanosystems present distinct advantages in overcoming BBB challenges, offering enhanced drug efficacy, reduced side effects, improved stability, and controlled release. Despite their promise, challenges persist, such as the BBB's regional variability hindering uniform drug distribution. Efflux transporters can also limit therapeutic agent efficacy, while nanosystem toxicity necessitates rigorous safety evaluations. Understanding the long-term impact of nanomaterials on the brain remains crucial. Additionally, addressing nanosystem scalability, cost-effectiveness, and safety profiles is vital for widespread clinical implementation. This review delves into the advancements and obstacles of advanced nanosystems in targeted drug delivery for neurodegenerative diseases and cancer therapy, with a focus on overcoming the BBB.

Hippocampal proteome comparison of infant and adult Fmr1 deficiency mice reveals adult-related changes associated with postsynaptic density

Deficiency in fragile X mental retardation 1 (Fmr1) leads to loss of its encoded protein FMRP and causes fragile X syndrome (FXS) by dysregulating its target gene expression in an age-related fashion. Using comparative proteomic analysis, this study identified 105 differentially expressed proteins (DEPs) in the hippocampus of postnatal day 7 (P7) Fmr1-/y mice and 306 DEPs of P90 Fmr1-/y mice. We found that most DEPs in P90 hippocampus were not changed in P7 hippocampus upon FMRP absence, and some P90 DEPs exhibited diverse proteophenotypes with abnormal expression of protein isoform or allele variants. Bioinformatic analyses showed that the P7 DEPs were mainly enriched in fatty acid metabolism and oxidoreductase activity and nutrient responses; whereas the P90 PEPs (especially down-regulated DEPs) were primarily enriched in postsynaptic density (PSD), neuronal projection development and synaptic plasticity. Interestingly, 25 of 30 down-regulated PSD proteins present in the most enriched protein to protein interaction network, and 6 of them (ANK3, ATP2B2, DST, GRIN1, SHANK2 and SYNGAP1) are both FMRP targets and autism candidates. Therefore, this study suggests age-dependent alterations in hippocampal proteomes upon loss of FMRP that may be associated with the pathogenesis of FXS and its related disorders. SIGNIFICANCE: It is well known that loss of FMRP resulted from Fmr1 deficiency leads to fragile X syndrome (FXS), a common neurodevelopmental disorder accompanied by intellectual disability and autism spectrum disorder (ASD). FMRP exhibits distinctly spatiotemporal patterns in the hippocampus between early development and adulthood, which lead to distinct dysregulations of gene expression upon loss of FMRP at the two age stages potentially linked to age-related phenotypes. Therefore, comparison of hippocampal proteomes between infancy and adulthood is valuable to provide insights into the early causations and adult-dependent consequences for FXS and ASD. Using a comparative proteomic analysis, this study identified 105 and 306 differentially expressed proteins (DEPs) in the hippocampi of postnatal day 7 (P7) and P90 Fmr1-/y mice, respectively. Few overlapping DEPs were identified between P7 and P90 stages, and the P7 DEPs were mainly enriched in the regulation of fatty acid metabolism and oxidoreduction, whereas the P90 DEPs were preferentially enriched in the regulation of synaptic formation and plasticity. Particularly, the up-regulated P90 proteins are primarily involved in immune responses and neurodegeneration, and the down-regulated P90 proteins are associated with postsynaptic density, neuron projection and synaptic plasticity. Our findings suggest that distinctly changed proteins in FMRP-absence hippocampus between infancy and adulthood may contribute to age-dependent pathogenesis of FXS and ASD.

Study on the underlying molecular mechanism of benzene-induced nervous system damage in mice based on tandem mass tag (TMT) proteomics

Benzene is known to be a common toxic industrial chemical, and prolonged benzene exposure may cause nervous system damage. At present, there were few studies on benzene-induced neurological damage. This research aimed to identify the protein biomarkers to explore the mechanism of nervous system damage caused by benzene. We established a benzene poisoning model of C57 mice by gavage of benzene-peanut oil suspension and identified differentially expressed proteins (DEPs) in brain tissue using tandem mass tag (TMT) proteomics. The results showed a significant weight loss and decrease in leukocyte and neutrophil counts in benzene poisoning mice compared to the control group. We also observed local cerebral oedema and small vessel occlusion in the cerebral white matter of benzene poisoning mice. TMT proteomic results showed that a total 6,985 proteins were quantified, with a fold change (FC) > 1.2 (or < 1/1.2) and P value <0.05 were considered as DEPs. Compared with the control group, we identified 43 DEPs, comprising 14 upregulated and 29 downregulated proteins. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis results showed that the candidate proteins were mainly involved in cholesterol metabolism, complement and coagulation cascades, african trypanosomiasis, PPAR signaling pathway, and vitamin digestion and absorption. Three proteins, 2-hydroxyacylsphingosine 1-beta-galactosyltransferase (UGT8), Apolipoprotein A-I (APOA1) and Complement C3 (C3) were validated using immunoblotting and immunohistochemical. In conclusion, our study preliminarily investigated the mechanism of benzene toxicity to the nervous system by analyzing DEPs changes in the brain.

The Association between High-density Lipoproteins and Periodontitis

Periodontitis is one of the most typical chronic dental diseases. This inflammatory disease can change various functions of immune cells and impair lipid metabolism through proinflammatory cytokines. High-Density Lipoprotein (HDL) is considered protective of the cardiovascular system. It has anti-thrombotic and anti-inflammatory effects. In this article, we have reviewed the association between periodontitis and HDL. Various studies have demonstrated a reverse relationship between inflammatory cytokines and HDL. HDL contains antioxidative enzymes and proteins, whereas periopathogens impair HDL's antioxidant function. The presence of periodontal bacteria is associated with a low HDL level in patients with periodontitis. Genetic variants in the interleukin- 6 (IL)-6 gene and cytochrome (CYP)1A1 rs1048943 gene polymorphism are associated with HDL levels and periodontal status. Studies showed that HDL levels improve after treatment for periodontitis. On the one hand, periodontal pathogenic bacteria and their metabolites and pro-inflammatory cytokines from periodontal infection can result in various disorders of lipid metabolism and lipid peroxidation. On the other hand, hyperlipidemia and lipid peroxidation stimulate proinflammatory cytokines, resulting in oxidative stress and delayed wound healing, making individuals susceptible to periodontitis.

Hippocampal neurogenesis and Arc expression are enhanced in high-fat fed prepubertal female pigs by a diet including omega-3 fatty acids and Bifidobacterium breve CECT8242

PURPOSE

Obesity during childhood has become a pandemic disease, mainly caused by a diet rich in sugars and fatty acids. Among other negative effects, these diets can induce cognitive impairment and reduce neuroplasticity. It is well known that omega-3 and probiotics have a beneficial impact on health and cognition, and we have hypothesized that a diet enriched with Bifidobacterium breve and omega-3 could potentiate neuroplasticity in prepubertal pigs on a high-fat diet.

METHODS

Young female piglets were fed during 10 weeks with: standard diet (T1), high-fat (HF) diet (T2), HF diet including B. breve CECT8242 (T3) and HF diet including the probiotic and omega-3 fatty acids (T4). Using hippocampal sections, we analyzed by immunocytochemistry the levels of doublecortin (DCX) to study neurogenesis, and activity-regulated cytoskeleton-associated protein (Arc) as a synaptic plasticity related protein.

RESULTS

No effect of T2 or T3 was observed, whereas T4 increased both DCX+ cells and Arc expression. Therefore, a diet enriched with supplements of B. breve and omega-3 increases neurogenesis and synaptic plasticity in prepubertal females on a HF diet from nine weeks of age to sexual maturity. Furthermore, the analysis of serum cholesterol and HDL indicate that neurogenesis was related to lipidic demand in piglets fed with control or HF diets, but the neurogenic effect induced by the T4 diet was exerted by mechanisms independent of this lipidic demand.

CONCLUSION

Our results show that the T4 dietary treatment is effective in potentiating neural plasticity in the dorsal hippocampus of prepubertal females on a HF diet.

The potential of CYP46A1 as a novel therapeutic target for neurological disorders: An updated review of mechanisms

Cholesterol is a key component of the cell membrane that impacts the permeability, fluidity, and functions of membrane-bound proteins. It also participates in synaptogenesis, synaptic function, axonal growth, dendrite outgrowth, and microtubule stability. Cholesterol biosynthesis and metabolism are in balance in the brain. Its metabolism in the brain is mediated mainly by CYP46A1 or cholesterol 24-hydroxylase. It is responsible for eliminating about 80% of the cholesterol excess from the human brain. CYP46A1 converts cholesterol to 24S-hydroxycholesterol (24HC) that readily crosses the blood-brain barrier and reaches the liver for the final elimination process. Studies show that cholesterol and 24HC levels change during neurological diseases and conditions. So, it was hypothesized that inhibition or activation of CYP46A1 would be an effective therapeutic strategy. Accordingly, preclinical studies, using genetic and pharmacological interventions, assessed the role of CYP46A1 in main neurodegenerative disorders such as Parkinson's disease, Huntington's disease, Alzheimer's disease, multiple sclerosis, spinocerebellar ataxias, and amyotrophic lateral sclerosis. In addition, its role in seizures and brain injury was evaluated. The recent development of soticlestat, as a selective and potent CYP46A1 inhibitor, with significant anti-seizure effects in preclinical and clinical studies, suggests the importance of this target for future drug developments. Previous studies have shown that both activation and inhibition of CYP46A1 are of therapeutic value. This article, using recent studies, highlights the role of CYP46A1 in various brain diseases and insults.

Crosstalk between neurological, cardiovascular, and lifestyle disorders: insulin and lipoproteins in the lead role

Insulin resistance and impaired lipoprotein metabolism contribute to a plethora of metabolic and cardiovascular disorders. These alterations have been extensively linked with poor lifestyle choices, such as consumption of a high-fat diet, smoking, stress, and a redundant lifestyle. Moreover, these are also known to increase the co-morbidity of diseases like Type 2 diabetes mellitus and atherosclerosis. Under normal physiological conditions, insulin and lipoproteins exert a neuroprotective role in the central nervous system. However, the tripping of balance between the periphery and center may alter the normal functioning of the brain and lead to neurological disorders such as Alzheimer's disease, Parkinson's disease, stroke, depression, and multiple sclerosis. These neurological disorders are further characterized by certain behavioral and molecular changes that show consistent overlap with alteration in insulin and lipoprotein signaling pathways. Therefore, targeting these two mechanisms not only reveals a way to manage the co-morbidities associated with the circle of the metabolic, central nervous system, and cardiovascular disorders but also exclusively work as a disease-modifying therapy for neurological disorders. In this review, we summarize the role of insulin resistance and lipoproteins in the progression of various neurological conditions and discuss the therapeutic options currently in the clinical pipeline targeting these two mechanisms; in addition, challenges faced in designing these therapeutic approaches have also been touched upon briefly.

Iron deposition heterogeneity in extrapyramidal system assessed by quantitative susceptibility mapping in Parkinson’s disease patients with type 2 diabetes mellitus

Purpose

Excessive brain iron depositions were found in both patients with Parkinson’s disease (PD) and those with type 2 diabetes mellitus (T2DM). The present study aimed to explore iron deposition and heterogeneity in the extrapyramidal system in PD patients with T2DM using quantitative susceptibility mapping (QSM) and further to reveal the effect of T2DM on the changes in brain iron in patients with PD.

Materials and methods

A total of 38 PD patients with T2DM (PDDM), 30 PD patients without T2DM (PDND), and 20 asymptomatic control subjects (CSs) were recruited for this study. All subjects underwent multiple MRI sequences involving enhanced gradient echo T2 star weighted angiography (ESWAN). The magnetic sensitivity values (MSV) and volume of the whole nuclei (MSV_W, V_W) and high iron region (MSV_RII, V_RII) were measured on the bilateral caudate nucleus (CN), the putamen (PUT), the globus pallidus (GP), the substantia nigra (SN), the red nucleus (RN) and the dentate nucleus (DN). Clinical and laboratory data were recorded, especially for the Hoehn and Yahr (H-Y) stage, the Montreal Cognitive Assessment (MoCA), the Mini-Mental State Examination (MMSE), the Hamilton Depression Rating Scale (HAMD), and the Hamilton Anxiety Rating Scale (HAMA). All QSM data were compared between PDDM and PDND groups and correlated with clinical and laboratory data.

Results

Compared to the PDND group, the V_RII/V_W of the left CN was significantly increased in the PDDM group. Significantly higher MSV_W and MSV_RII were also found in the PDDM group, including bilateral SN of MSV_W, right PUT, and bilateral CN, GP, and SN of MSV_RII. The H-Y stage of the PDDM group was significantly higher than that of the PDND group. The MSV_RII of bilateral RN of the PDDM group was positively correlated with the HAMA scores. HDL, DBP, and SBP levels were associated with MSV_RII of right CN in the PDDM group.

Conclusion

T2DM could aggravate the disease severity and anxiety in patients with PD. The iron distribution of deep gray matter nuclei in PD patients with T2DM was significantly heterogeneous, which was related to blood pressure and blood lipids.

HDL-like-Mediated Cell Cholesterol Trafficking in the Central Nervous System and Alzheimer's Disease Pathogenesis

The main aim of this work is to review the mechanisms via which high-density lipoprotein (HDL)-mediated cholesterol trafficking through the central nervous system (CNS) occurs in the context of Alzheimer’s disease (AD). Alzheimer’s disease is characterized by the accumulation of extracellular amyloid beta (Aβ) and abnormally hyperphosphorylated intracellular tau filaments in neurons. Cholesterol metabolism has been extensively implicated in the pathogenesis of AD through biological, epidemiological, and genetic studies, with the APOE gene being the most reproducible genetic risk factor for the development of AD. This manuscript explores how HDL-mediated cholesterol is transported in the CNS, with a special emphasis on its relationship to Aβ peptide accumulation and apolipoprotein E (ApoE)-mediated cholesterol transport. Indeed, we reviewed all existing works exploring HDL-like-mediated cholesterol efflux and cholesterol uptake in the context of AD pathogenesis. Existing data seem to point in the direction of decreased cholesterol efflux and the impaired entry of cholesterol into neurons among patients with AD, which could be related to impaired Aβ clearance and tau protein accumulation. However, most of the reviewed studies have been performed in cells that are not physiologically relevant for CNS pathology, representing a major flaw in this field. The ApoE4 genotype seems to be a disruptive element in HDL-like-mediated cholesterol transport through the brain. Overall, further investigations are needed to clarify the role of cholesterol trafficking in AD pathogenesis.

Serum levels of apolipoprotein A-I and E are associated with postoperative delirium: A post hoc analysis

Postoperative delirium is a common complication for elderly patients. Detection of phosphorylated neurofilament heavy subunit in the serum reflects axonal damage with postoperative delirium. Although it has been implicated that serum apolipoprotein levels might be associated with senile cognitive disorder, its role in the development of delirium has not been fully investigated. This study examined the association of apolipoproteins with delirium after surgery. This was a post hoc analysis of 117 patients who participated in a prospective observational study of delirium in patients undergoing cancer surgery. Patients were clinically assessed for delirium within the first 5 days of surgery. Serum levels of apolipoprotein A-I, B, and E were measured on postoperative day 3. Forty-one patients (35%) were clinically diagnosed with postoperative delirium. Serum levels of apolipoprotein A-I and B were increased in patients with delirium whereas those of apolipoprotein E were decreased. These changes in apolipoprotein A-I and E levels were associated with the presence of phosphorylated neurofilament heavy subunit in the serum, and were significantly associated with delirium (A-I: adjusted odds ratio [aOR], 6.238; 95% confidence interval [CI], 2.766-20.68; P < .0001; E: aOR, 0.253; 95% CI, 0.066-0.810; P = .0193). A combination of apolipoprotein A-I and E offers significant discrimination between delirium and nondelirium with high accuracy (area under the curve, 0.8899). Serum apolipoprotein A-I and E levels were associated with delirium and the presence of phosphorylated neurofilament heavy subunit in serum. Therefore, apolipoproteins might be useful biomarkers of postoperative delirium.

Lipoproteins in the Central Nervous System: From Biology to Pathobiology

The brain, as one of the most lipid-rich organs, heavily relies on lipid transport and distribution to maintain homeostasis and neuronal function. Lipid transport mediated by lipoprotein particles, which are complex structures composed of apolipoproteins and lipids, has been thoroughly characterized in the periphery. Although lipoproteins in the central nervous system (CNS) were reported over half a century ago, the identification of APOE4 as the strongest genetic risk factor for Alzheimer's disease has accelerated investigation of the biology and pathobiology of lipoproteins in the CNS. This review provides an overview of the different components of lipoprotein particles, in particular apolipoproteins, and their involvements in both physiological functions and pathological mechanisms in the CNS.

Metabolism and the Effect of Animal-Derived Oxysterols in the Diet on the Development of Alzheimer's Disease

BACKGROUND

The rapid worldwide increase in the incidence of Alzheimer's disease is associated with changing nutrition patterns. Recently, some articles have highlighted the link between Alzheimer's disease and dietary cholesterol. It was found that elevated levels of some of its fractions in the brain and circulation affect metabolism.

SUMMARY

Previous studies have considered the relationship between Alzheimer's disease and oxidized cholesterol molecules in the brain. To date, there are limited data available on the relationship between oxidized cholesterol in the brain and Alzheimer's disease. There is a link between a diet high in cholesterol and its oxidized forms, leading to hypercholesterolemia, which is one of significant risk factors of dementia, and Alzheimer's disease. Oxidized cholesterol can be absorbed in the small intestine and cross the blood-brain barrier, leading to increased inflammation and endogenous oxidative process. Animal-origin foods are sources of oxidized cholesterol, with cholesterol oxidation beginning already after slaughter and occurring during storage and processing.

KEY MESSAGES

High-heat food preparation and storage of cooked products in the refrigerator followed by subsequent heating may significantly increase the amount of oxidized cholesterol products. Therefore, a diet low in cholesterol oxidation products and high in plants with antioxidative properties seems to be most preventable and should be implemented as early as possible.

The Current Status of Research on High-Density Lipoproteins (HDL): A Paradigm Shift from HDL Quantity to HDL Quality and HDL Functionality

The quantity of high-density lipoproteins (HDL) is represented as the serum HDL-C concentration (mg/dL), while the HDL quality manifests as the diverse features of protein and lipid content, extent of oxidation, and extent of glycation. The HDL functionality represents several performance metrics of HDL, such as antioxidant, anti-inflammatory, and cholesterol efflux activities. The quantity and quality of HDL can change during one's lifetime, depending on infection, disease, and lifestyle, such as dietary habits, exercise, and smoking. The quantity of HDL can change according to age and gender, such as puberty, middle-aged symptoms, climacteric, and the menopause. HDL-C can decrease during disease states, such as acute infection, chronic inflammation, and autoimmune disease, while it can be increased by regular aerobic exercise and healthy food consumption. Generally, high HDL-C at the normal level is associated with good HDL quality and functionality. Nevertheless, high HDL quantity is not always accompanied by good HDL quality or functionality. The HDL quality concerns the morphology of the HDL, such as particle size, shape, and number. The HDL quality also depends on the composition of the HDL, such as apolipoproteins (apoA-I, apoA-II, apoC-III, serum amyloid A, and α-synuclein), cholesterol, and triglyceride. The HDL quality is also associated with the extent of HDL modification, such as glycation and oxidation, resulting in the multimerization of apoA-I, and the aggregation leads to amyloidogenesis. The HDL quality frequently determines the HDL functionality, which depends on the attached antioxidant enzyme activity, such as the paraoxonase and cholesterol efflux activity. Conventional HDL functionality is regression, the removal of cholesterol from atherosclerotic lesions, and the removal of oxidized species in low-density lipoproteins (LDL). Recently, HDL functionality was reported to expand the removal of β-amyloid plaque and inhibit α-synuclein aggregation in the brain to attenuate Alzheimer's disease and Parkinson's disease, respectively. More recently, HDL functionality has been associated with the susceptibility and recovery ability of coronavirus disease 2019 (COVID-19) by inhibiting the activity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The appearance of dysfunctional HDL is frequently associated with many acute infectious diseases and chronic aging-related diseases. An HDL can be a suitable biomarker to diagnose many diseases and their progression by monitoring the changes in its quantity and quality in terms of the antioxidant and anti-inflammatory abilities. An HDL can be a protein drug used for the removal of plaque and as a delivery vehicle for non-soluble drugs and genes. A dysfunctional HDL has poor HDL quality, such as a lower apoA-I content, lower antioxidant ability, smaller size, and ambiguous shape. The current review analyzes the recent advances in HDL quantity, quality, and functionality, depending on the health and disease state during one's lifetime.

Emerging role of HDL in brain cholesterol metabolism and neurodegenerative disorders

High-density lipoproteins (HDLs play a key role in cholesterol homeostasis maintenance in the central nervous system (CNS), by carrying newly synthesized cholesterol from astrocytes to neurons, to support their lipid-related physiological functions. As occurs for plasma HDLs, brain lipoproteins are assembled through the activity of membrane cholesterol transporters, undergo remodeling mediated by specific enzymes and transport proteins, and finally deliver cholesterol to neurons by a receptor-mediated internalization process. A growing number of evidences indicates a strong association between alterations of CNS cholesterol homeostasis and neurodegenerative disorders, in particular Alzheimer's disease (AD), and a possible role in this relationship may be played by defects in brain HDL metabolism. In the present review, we summarize and critically examine the current state of knowledge on major modifications of HDL and HDL-mediated brain cholesterol transport in AD, by taking into consideration the individual steps of this process. We also describe potential and encouraging HDL-based therapies that could represent new therapeutic strategies for AD treatment. Finally, we revise the main plasma and brain HDL modifications in other neurodegenerative disorders including Parkinson's disease (PD), Huntington's disease (HD), and frontotemporal dementia (FTD).

Random-Forest-Algorithm-Based Applications of the Basic Characteristics and Serum and Imaging Biomarkers to Diagnose Mild Cognitive Impairment

Background

Mild cognitive impairment (MCI) is considered the early stage of Alzheimer's Disease (AD). The purpose of our study was to analyze the basic characteristics and serum and imaging biomarkers for the diagnosis of MCI patients as a more objective and accurate approach.

Methods

The Montreal Cognitive Test was used to test 119 patients aged ≥65. Such serum biomarkers were detected as preprandial blood glucose, triglyceride, total cholesterol, Aβ1-40, Aβ1-42, and P-tau. All the subjects were scanned with 1.5T MRI (GE Healthcare, WI, USA) to obtain DWI, DTI, and ASL images. DTI was used to calculate the anisotropy fraction (FA), DWI was used to calculate the apparent diffusion coefficient (ADC), and ASL was used to calculate the cerebral blood flow (CBF). All the images were then registered to the SPACE of the Montreal Neurological Institute (MNI). In 116 brain regions, the medians of FA, ADC, and CBF were extracted by automatic anatomical labeling. The basic characteristics included gender, education level, and previous disease history of hypertension, diabetes, and coronary heart disease. The data were randomly divided into training sets and test ones. The recursive random forest algorithm was applied to the diagnosis of MCI patients, and the recursive feature elimination (RFE) method was used to screen the significant basic features and serum and imaging biomarkers. The overall accuracy, sensitivity, and specificity were calculated, respectively, and so were the ROC curve and the area under the curve (AUC) of the test set.

Results

When the variable of the MCI diagnostic model was an imaging biomarker, the training accuracy of the random forest was 100%, the correct rate of the test was 86.23%, the sensitivity was 78.26%, and the specificity was 100%. When combining the basic characteristics, the serum and imaging biomarkers as variables of the MCI diagnostic model, the training accuracy of the random forest was found to be 100%; the test accuracy was 97.23%, the sensitivity was 94.44%, and the specificity was 100%. RFE analysis showed that age, Aβ1-40, and cerebellum_4_6 were the most important basic feature, serum biomarker, imaging biomarker, respectively.

Conclusion

Imaging biomarkers can effectively diagnose MCI. The diagnostic capacity of the basic trait biomarkers or serum biomarkers for MCI is limited, but their combination with imaging biomarkers can improve the diagnostic capacity, as indicated by the sensitivity of 94.44% and the specificity of 100% in our model. As a machine learning method, a random forest can help diagnose MCI effectively while screening important influencing factors.

Levels of Angiotensin-Converting Enzyme and Apolipoproteins Are Associated with Alzheimer's Disease and Cardiovascular Diseases

Angiotensin-converting enzyme-1 (ACE1) and apolipoproteins (APOs) may play important roles in the development of Alzheimer's disease (AD) and cardiovascular diseases (CVDs). This study aimed to examine the associations of AD, CVD, and endocrine-metabolic diseases (EMDs) with the levels of ACE1 and 9 APO proteins (ApoAI, ApoAII, ApoAIV, ApoB, ApoCI, ApoCIII, ApoD, ApoE, and ApoH). Non-Hispanic white individuals including 109 patients with AD, 356 mild cognitive impairment (MCI), 373 CVD, 198 EMD and controls were selected from the Alzheimer's Disease Neuroimaging Initiative (ADNI) dataset. Multivariable general linear model (GLM) was used to examine the associations. ApoE ε4 allele was associated with AD, as well as ApoAIV, ApoB and ApoE proteins, but not associated with CVD and EMD. Both AD and CVD were associated with levels of ACE1, ApoB, and ApoH proteins. AD, MCI and EMD were associated with levels of ACE1, ApoAII, and ApoE proteins. This is the first study to report associations of ACE1 and several APO proteins with AD, MCI, CVD and EMD, respectively, including upregulated and downregulated protein levels. In conclusion, as specific or shared biomarkers, the levels of ACE1 and APO proteins are implicated for AD, CVD, EMD and ApoE ε4 allele. Further studies are required for validation to establish reliable biomarkers for these health conditions.

Effect of age stratification on the association between carotid intima-media thickness and cognitive impairment in Chinese hypertensive patients: new insight from the secondary analysis of the China Stroke Primary Prevention Trial (CSPPT)

The current study aimed to explore the association between carotid intima-media thickness (CIMT) and cognitive function assessed by the Mini-Mental State Examination (MMSE) and to examine possible effect modifiers in hypertensive patients. A total of 14,322 hypertensive participants (mean age 64.2 ± 7.4 years; 40.9% male) from the China Stroke Primary Prevention Trial (CSPPT) were included in the final analysis. CIMT was measured by ultrasound, and data were collected at the last follow-up visit; MMSE was used to evaluate cognitive function. Nonparametric smoothing plots, multivariate linear regression analysis, subgroup analyses and interaction testing were performed to examine the relationship between the CIMI and cognitive function and effect modification. The mean CIMT was 0.74 ± 0.11 mm, and the mean MMSE score was 23.5 ± 4.8. There was a significant interaction (P interaction < 0.05) in both male and female populations stratified by age (<60 vs. ≥60 years), and higher CIMT was significantly associated with decreased MMSE scores only in participants aged ≥60 years (male: β = -2.29, 95% CI -3.23 to -1.36; female: β = -1.96, 95% CI -2.97 to -0.95). Males with abnormal HDL-C showed a stronger negative association (β = -3.16, 95% CI -4.85 to -1.47) than those with normal HDL-C (normal vs. abnormal, P for interaction = 0.004). We observed that increased CIMT was significantly associated with cognitive impairment in the hypertensive population, especially among individuals with an age greater than 60 years and HDL-C deficiency. Overall, upon diagnosis of hypertension, treatment should start at the earliest opportunity to prevent end-organ damage and cognitive decline.

Metabolic indices in schizophrenia: Association of negative symptoms with higher HDL cholesterol in female patients

OBJECTIVES

Negative symptoms of schizophrenia can be related to metabolic abnormalities. The study aimed to assess negative symptoms using the Positive and Negative Syndrome Scale (PANSS) and the Brief Negative Symptoms Scale (BNSS), and their relationship with body mass index (BMI) and lipid indices, in male and female schizophrenic patients.

METHODS

Fifty chronic schizophrenia patients (29 males, 21 females) were included. They have mild to moderate severity of the illness (total PANSS score <80), and received unchanged pharmacological treatment in the last three weeks. Psychopathology symptoms were assessed using the PANSS and BNSS. The measurements of BMI and serum lipids were done in all patients.

RESULTS

In female patients, a significant positive correlation between the intensity of negative symptoms measured by the PANSS and BNSS scales and the concentration of high-density lipoprotein (HDL) cholesterol, and a trend for negative correlation with BMI was observed. Such correlations were not found in male patients.

CONCLUSIONS

Assessing the negative symptoms of schizophrenia, and investigating the relationship of these symptoms with metabolic indices, we showed distinctive features in male and female schizophrenia patients. The positive correlation between negative symptoms and HDL cholesterol in female patients needs to be confirmed in further studies.

Structural and Functional Impairments of Reconstituted High-Density Lipoprotein by Incorporation of Recombinant β-Amyloid42

Beta (β)-amyloid (Aβ) is a causative protein of Alzheimer’s disease (AD). In the pathogenesis of AD, the apolipoprotein (apo) A-I and high-density lipoprotein (HDL) metabolism is essential for the clearance of Aβ. In this study, recombinant Aβ42 was expressed and purified via the pET-30a expression vector and E.coli production system to elucidate the physiological effects of Aβ on HDL metabolism. The recombinant human Aβ protein (51 aa) was purified to at least 95% purity and characterized in either the lipid-free and lipid-bound states with apoA-I. Aβ was incorporated into the reconstituted HDL (rHDL) (molar ratio 95:5:1, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC):cholesterol:apoA-I) with various apoA-I:Aβ ratios from 1:0 to 1:0.5, 1:1 and 1:2. With an increasing molar ratio of Aβ, the α-helicity of apoA-I was decreased from 62% to 36% with a red shift of the Trp wavelength maximum fluorescence from 337 to 340 nm in apoA-I. The glycation reaction of apoA-I was accelerated further by the addition of Aβ. The treatment of fructose and Aβ caused more multimerization of apoA-I in the lipid-free state and in HDL. The phospholipid-binding ability of apoA-I was impaired severely by the addition of Aβ in a dose-dependent manner. The phagocytosis of LDL into macrophages was accelerated more by the presence of Aβ with the production of more oxidized species. Aβ severely impaired tissue regeneration, and a microinjection of Aβ enhanced embryotoxicity. In conclusion, the beneficial functions of apoA-I and HDL were severely impaired by the addition of Aβ via its detrimental effect on secondary structure. The impairment of HDL functionality occurred more synergistically by means of the co-addition of fructose and Aβ.

Optimizing clinical phenotyping to better delineate the complex relationship between type 2 diabetes and Alzheimer’s disease

Alzheimer’s disease (AD) is the most common form of dementia, and its prevalence is increasing rapidly. According to the Alzheimer’s Association, over 5 million adults in the United States over the age of 65 years currently have AD, and this number is expected to exceed 13 million by 2050 in the absence of novel, preventative strategies. Epidemiologic studies have implicated the presence of type 2 diabetes mellitus (T2DM) specifically at midlife as a key modifiable risk factor for AD, and AD may increase risk of dysglycemia and T2DM. However, data have been inconsistent with regard to the magnitude of AD risk attributable to T2DM, and the pathways underlying this apparent relationship remain poorly understood. Elucidating the impact of T2DM on AD risk and progression requires greater attention to the myriad facets of T2DM pathophysiology, its comorbid conditions, and attendant treatment modalities, all of which may differentially impact the relationships among T2DM, cognitive decline, and AD. This mini‐review will summarize the discrete facets of T2DM that may influence AD risk and highlight the importance of careful clinical phenotyping in both epidemiologic and interventional studies to better delineate the key pathways and mechanisms linking T2DM and AD.

The role of high-density lipoprotein cholesterol, apolipoprotein A and paraoxonase-1 in the pathophysiology of neuroprogressive disorders

Lowered high-density lipoprotein (HDL) cholesterol has been reported in major depressive disorder, bipolar disorder, first episode of psychosis, and schizophrenia. HDL, its major apolipoprotein component, ApoA1, and the antioxidant enzyme paraoxonase (PON)1 (which is normally bound to ApoA1) all have anti-atherogenic, antioxidant, anti-inflammatory, and immunomodulatory roles, which are discussed in this paper. The paper details the pathways mediating the anti-inflammatory effects of HDL, ApoA1 and PON1 and describes the mechanisms leading to compromised HDL and PON1 levels and function in an environment of chronic inflammation. The molecular mechanisms by which changes in HDL, ApoA1 and PON1 might contribute to the pathophysiology of the neuroprogressive disorders are explained. Moreover, the anti-inflammatory actions of ApoM-mediated sphingosine 1-phosphate (S1P) signalling are reviewed as well as the deleterious effects of chronic inflammation and oxidative stress on ApoM/S1P signalling. Finally, therapeutic interventions specifically aimed at improving the levels and function of HDL and PON1 while reducing levels of inflammation and oxidative stress are considered. These include the so-called Mediterranean diet, extra virgin olive oil, polyphenols, flavonoids, isoflavones, pomegranate juice, melatonin and the Mediterranean diet combined with the ketogenic diet.

Effect of a Synbiotic Supplement on Fear Response and Memory Assessment of Broiler Chickens Subjected to Heat Stress

The aim of this study was to evaluate the effect of a synbiotic containing a probiotic (Enterococcus faecium, Pediococcus acidilactici, Bifidobacterium animalis, and Lactobacillus reuteri) and a prebiotic (fructooligosaccharides) on fear response, memory assessment, and selected stress indicators in broilers subjected to heat stress. A total of 360 1-day-old Ross 708 chicks were evenly divided among three treatments: a basal diet mixed with a synbiotic at 0 (G-C), 0.5 (G-0.5X), and 1.0 (G-1.0X) g/kg. After 15 d, the broilers were exposed to 32 °C for 9 h daily until 42 d. The object memory test was conducted at 15 day; touch, novel object, and isolation tests were conducted at 35 day; tonic immobility (TI) took place at 41 day. At 42 day, plasma corticosterone and tryptophan concentrations and heterophile/lymphocyte (H/L) ratios were measured. Compared to controls, synbiotic-fed broilers, regardless of concentration, had a shorter latency to make the first vocalization, with higher vocalization rates during the isolation test (p = 0.001). the G-1.0 group had the lowest H/L ratio (p = 0.001), but higher plasma tryptophan concentrations and a greater number of birds could reach the observer during the touch test (p = 0.001 and 0.043, respectively). The current results indicate that the synbiotic can be used as a growth promoter to reduce the fear response and stress state of heat-stressed broilers.

Apolipoprotein A-I in mouse cerebrospinal fluid derives from the liver and intestine via plasma high-density lipoproteins assembled by ABCA1 and LCAT

Apolipoprotein (apo) A-I, the major structural protein of high-density lipoprotein (HDL), is present in human and mouse cerebrospinal fluid (CSF) despite its lack of expression in brain cells. To identify the origin of apoA-I in CSF, we generated intestine-specific and liver-specific Apoa1 knockout mice (Apoa1^ΔInt and Apoa1^Δliv mice, respectively). Lipoprotein profiles of Apoa1^ΔInt and Apoa1^ΔLiv mice resembled those of control littermates, whereas knockout of Apoa1 in both intestine and liver (Apoa1^ΔIntΔLiv ) resulted in a 60-percent decrease in HDL-cholesterol levels, thus strongly mimicking the Apoa1^-/- mice. Immunoassays revealed that mouse apoA-I was not present in the CSF of the Apoa1^ΔIntΔLiv mice. Furthermore, apoA-I levels in CSF were highly correlated with plasma spherical HDL levels, which were regulated by ABCA1 and LCAT. Collectively, these results suggest that apoA-I protein in CSF originates in liver and small intestine and is taken up from the plasma.

Alzheimer's Disease: Protective Effects of Mycobacterium vaccae, a Soil-Derived Mycobacterium with Anti-Inflammatory and Anti-Tubercular Properties, on the Proteomic Profiles of Plasma and Cerebrospinal Fluid in Rats

BACKGROUND

Alzheimer's disease (AD) is an inflammatory neurodegenerative disease that may be associated with prior bacterial infections. Microbial "old friends" can suppress exaggerated inflammation in response to disease-causing infections or increase clearance of pathogens such as Mycobacterium tuberculosis, which causes tuberculosis (TB). One such "old friend" is Mycobacterium vaccae NCTC 11659, a soil-derived bacterium that has been proposed either as a vaccine for prevention of TB, or as immunotherapy for the treatment of TB when used alongside first line anti-TB drug treatment.

OBJECTIVE

The goal of this study was to use a hypothesis generating approach to explore the effects of M. vaccae on physiological changes in the plasma and cerebrospinal fluid (CSF).

METHODS

Liquid chromatography-tandem mass spectrometry-based proteomics were performed in plasma and CSF of adult male rats after immunization with a heat-killed preparation of M. vaccae NCTC 11659 or borate-buffered saline vehicle. Gene enrichment analysis and analysis of protein-protein interactions were performed to integrate physiological network changes in plasma and CSF. We used RT-qPCR to assess immune and metabolic gene expression changes in the hippocampus.

RESULTS

In both plasma and CSF, immunization with M. vaccae increased proteins associated with immune activation and downregulated proteins corresponding to lipid (including phospholipid and cholesterol) metabolism. Immunization with M. vaccae also increased hippocampal expression of interleukin-4 (IL-4) mRNA, implicating anti-inflammatory effects in the central nervous system.

CONCLUSION

M. vaccae alters host immune activity and lipid metabolism. These data are consistent with the hypothesis that microbe-host interactions may protect against possible infection-induced, inflammation-related cognitive impairments.

Association of inflammatory factors and aging in Parkinson's disease

BACKGROUND

Parkinson's disease as a common neurodegenerative disease, has been found to be related to inflammation. So we observed the characteristics of inflammatory indexes in patients with Parkinson's disease and investigated the relationship between inflammatory cytokines and clinical characteristics. Emerging data may reveal novel neuroinflammatory pathways and identify new targets for treatment of Parkinson's disease.

METHODS

We examined the inflammatory indexes in 183 patients and 89 healthy controls in association with clinical characteristics.

RESULTS

Patients had significantly higher levels of monocytes, neutrophils, high-sensitivity C-reactive protein, and monocyte-to-high-density lipoprotein ratios (p < 0.01) and lower levels of lymphocytes (p = 0.02) than the controls. There were no significant differences in age, leukocytes, high-density lipoprotein, or neutrophil-lymphocyte ratios between the two groups (p > 0.05). Multivariate logistic regression analysis of these indicators revealed that lymphocyte level was a protective factor (p = 0.025, OR=-0.679), while high-sensitivity C-reactive protein level was a risk factor (p = 0.000, OR=1.168) for Parkinson's disease. High-sensitivity C-reactive protein levels were higher in older Parkinson's disease patients.

CONCLUSION

High-sensitivity C-reactive protein is positively related to the risk of Parkinson's disease, especially in aging patients. High-sensitivity C-reactive protein is a potential biomarker for disease progression and treatment response for Parkinson's disease.

Choroid Plexus: The Orchestrator of Long-Range Signalling Within the CNS

Cerebrospinal fluid (CSF) is the liquid that fills the brain ventricles. CSF represents not only a mechanical brain protection but also a rich source of signalling factors modulating diverse processes during brain development and adulthood. The choroid plexus (CP) is a major source of CSF and as such it has recently emerged as an important mediator of extracellular signalling within the brain. Growing interest in the CP revealed its capacity to release a broad variety of bioactive molecules that, via CSF, regulate processes across the whole central nervous system (CNS). Moreover, CP has been also recognized as a sensor, responding to altered composition of CSF associated with changes in the patterns of CNS activity. In this review, we summarize the recent advances in our understanding of the CP as a signalling centre that mediates long-range communication in the CNS. By providing a detailed account of the CP secretory repertoire, we describe how the CP contributes to the regulation of the extracellular environment-in the context of both the embryonal as well as the adult CNS. We highlight the role of the CP as an important regulator of CNS function that acts via CSF-mediated signalling. Further studies of CP-CSF signalling hold the potential to provide key insights into the biology of the CNS, with implications for better understanding and treatment of neuropathological conditions.

Revealing a Novel Landscape of the Association Between Blood Lipid Levels and Alzheimer's Disease: A Meta-Analysis of a Case-Control Study

Objectives: Blood lipid profiles have been ambiguously reported as biomarkers of AD in recent years. This study was conducted to evaluate the correlation between blood lipid levels and AD in later-life and to explore the effectiveness and reliability of blood lipid profiles as biomarkers of AD. Methods: Database searching was conducted using PubMed, the Cochrane Library, EMBASE, and Medline. This study was designed following the Meta-analysis of Observational Studies in Epidemiology (MOOSE) criteria. Review Manager 5.3 (RevMan 5.3) software was adopted to perform meta-analysis evaluating the standard mean difference (SMD) with its 95% confidence intervals (CI). Results: A total of 5,286 participants were enrolled from 27 case-control studies in this meta-analysis. The pooled results demonstrated that total cholesterol (TC) level was significantly associated with AD in late-life (SMD = 0.17, 95% CI: [0.01, 0.32], P = 0.03), especially in the subgroup under 70 years old (SMD: 0.45, 95% CI: [0.11, 0.79], P = 0.01) and the subgroup of Western population (SMD: 0.29, 95% CI: [0.04, 0.53], P = 0.02). In the subgroup under 70 years old, the high-density lipoprotein cholesterol (HDL-C) level (SMD = -0.50, 95% CI: [-0.76, -0.25], P = 0.0001) and the low-density lipoprotein cholesterol (LDL-C) level (SMD = 0.59, 95% CI: [0.02, 1.16], P = 0.04) in the AD group were significantly lower and higher than in the control group, respectively. In the subgroup with a sample size larger than 100 subjects, the LDL-C level was significantly higher in AD patients than in the control elderly group (SMD = 0.31, 95% CI: [0.05, 0.56], P = 0.02). There was no significant association between triglyceride (TG) levels and AD in later-life (SMD = -0.00, 95% CI: [-0.12, 0.12], P = 1.00). Conclusion: TC can be a new predictive biomarker of AD or cognitive decline in later-life. Increased TC levels are found to be associated with an elevated risk of AD. Decreased HDL-C levels and increased LDL-C levels may relate to an elevated risk of AD in subjects aged 60-70. Further comprehensive researches will be necessary in the future.