Plasma oxidized low-density lipoprotein levels and risk of Alzheimer's disease

Fluid biomarkers of vascular cognitive Impairment: From vascular pathophysiology to potential clinical applications

Vascular cognitive impairment (VCI) refers to cognitive decline resulting from cerebrovascular pathology, affecting one or more cognitive domains. Chronic vascular risk factors and acute cerebrovascular events contribute significantly to this condition. Identifying fluid biomarkers indicative of vascular injury is crucial for early prevention, accurate diagnosis, and assessing treatment efficacy in VCI. Chronic vascular injury leads to arterial lesions, blood-brain barrier disruption, venous tortuosity and obstructed drainage, enlarged perivascular spaces, and impaired glymphatic drainage. This review explores biomarkers involved in VCI pathogenesis, including neurodegenerative proteins, inflammatory mediators, oxidative stress markers, metabolic byproducts, acute phase reactants, vasoactive neuropeptides, the cerebrospinal fluid/plasma albumin quotient, neurofilament light chain, circulating CD34 + cells, and miRNAs. Most biomarkers are derived from blood and cerebrospinal fluid, with the exception of 8-hydroxydeoxyguanosine, excreted in urine. Combining biomarkers from various fluid sources can enhance diagnostic accuracy for VCI. Given the interplay between blood buffering and renal excretion in biomarker production, we advocate for further research into urine-derived biomarkers. These may offer valuable insights for early detection of vascular changes and ultra-early prediction of VCI.

Linking oxysterols and different stages of mild cognitive impairment: insights from gut metabolites and N6-methyladenosine

BACKGROUND

Oxysterols, gut metabolites, and N6-methyladenosine (m6A) are extensively implicated in the pathogenesis of cognitive dysfunction, while their alterations in different stages of mild cognitive impairment (MCI) have not been elucidated. Therefore, this study was conducted to explore the associations of oxysterols, gut metabolites, and m6A methylation profiles in early MCI (EMCI) and late MCI (LMCI) individuals.

METHODS

Liquid chromatography-mass spectrometry, untargeted metabolomic analysis, and m6A mRNA Epitranscriptomic Microarray were used to detect the characteristics of serum oxysterols (n = 35/group), fecal gut metabolites (n = 30/group), and m6A in whole blood (n = 4/group) respectively. The concentration of serum β-amyloid (Aβ) was detected with ELISA (n = 25/group). The gene expression of amyloid precursor protein (APP) and its key enzyme β-secretase (BACE1) in whole blood were measured by quantitative real-time PCR (n = 25/group).

RESULTS

EMCIs and LMCIs, especially LMCIs, exhibited poorer performance in almost all global and multidimensional cognitive tests. Serum 27-hydroxycholesterol (27-OHC) and 24S-hydroxycholesterol (24S-OHC) were elevated in EMCI and LMCI groups. Changes in gut metabolites occurred mainly in the EMCI group, in which several gut metabolites, including Procyanidin dimer B7 and Phorbol myristate, were significantly decreased. The m6A methylation landscape of EMCIs and LMCIs obviously differed from Controls. Hypomethylated mRNAs accounted for the majority and were mainly accompanied by downregulated mRNAs, which was consistent with the downregulated expression of the m6A writer methyltransferase-like 4 (METTL4). 27-OHC and 24S-OHC combined with various gut metabolites significantly distinguished between MCI subgroups from healthy controls (EMCI/Control: AUC = 0.877; LMCI/Control: AUC = 0.952). Heatmap revealed the correlation between Phorbol myristate and differentially m6A-methylated mRNAs. Differentially expressed gut metabolites and methylated mRNAs were commonly enriched in 34 KEGG metabolic pathways, including cholesterol metabolism and neurodegenerative disease-related pathways.

CONCLUSIONS

Our study explored the altered oxysterols, gut metabolites, and m6A methylation and their associations in different stages of MCI. The potential function of aberrant gut metabolites in oxysterols and m6A methylation driving MCI progression warrants further mechanistic investigation.

Molecular biomarkers for vascular cognitive impairment and dementia

As disease-specific interventions for dementia are being developed, the ability to identify the underlying pathology and dementia subtypes is increasingly important. Vascular cognitive impairment and dementia (VCID) is the second most common cause of dementia after Alzheimer disease, but progress in identifying molecular biomarkers for accurate diagnosis of VCID has been relatively limited. In this Review, we examine the roles of large and small vessel disease in VCID, considering the underlying pathophysiological processes that lead to vascular brain injury, including atherosclerosis, arteriolosclerosis, ischaemic injury, haemorrhage, hypoperfusion, endothelial dysfunction, blood-brain barrier breakdown, inflammation, oxidative stress, hypoxia, and neuronal and glial degeneration. We consider the key molecules in these processes, including proteins and peptides, metabolites, lipids and circulating RNA, and consider their potential as molecular biomarkers alone and in combination. We also discuss the challenges in translating the promise of these biomarkers into clinical application.

Implication of Circulating Extracellular Vesicles-Bound Amyloid-β42 Oligomers in the Progression of Alzheimer's Disease

BACKGROUND

The perplex interrelation between circulating extracellular vesicles (cEVs) and amyloid-β (Aβ) deposits in the context of Alzheimer's disease (AD) is poorly understood.

OBJECTIVE

This study aims to 1) analyze the possible cross-linkage of the neurotoxic amyloid-β oligomers (oAβ) to the human cEVs, 2) identify cEVs corona proteins associated with oAβ binding, and 3) analyze the distribution and expression of targeted cEVs proteins in preclinical participants converted to AD 5 years later (Pre-AD).

METHODS

cEVs were isolated from 15 Pre-AD participants and 15 healthy controls selected from the Canadian Study of Health and Aging. Biochemical, clinical, lipid, and inflammatory profiles were measured. oAβ and cEVs interaction was determined by nanoparticle tracking analysis and proteinase K digestion. cEVs bound proteins were determined by ELISA.

RESULTS

oAβ were trapped by cEVs and were topologically bound to their external surface. We identified surface-exposed proteins functionally able to conjugate oAβ including apolipoprotein J (apoJ), apoE and RAGE, with apoJ being 30- to 130-fold higher than RAGE and apoE, respectively. The expression of cEVs apoJ was significantly lower in Pre-AD up to 5 years before AD onset.

CONCLUSION

Our findings suggest that cEVs might participate in oAβ clearance and that early dysregulation of cEVs could increase the risk of conversion to AD.

Plasma Cholesterol Levels as Potential Nutritional Biomarkers for Lewy Body Dementia

BACKGROUND

The relationship between cholesterol level and the risk of developing Alzheimer's disease has been well established, but the relationship between cholesterol level and Lewy body dementia (LBD) is still not well known.

OBJECTIVE

The aim of this case-control study was to explore the association between blood cholesterol levels and LBD in Chinese older adults.

METHODS

A total of 65 patients with LBD and 110 older adult controls were enrolled during the study period. The levels of triglyceride, total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and fasting glucose were measured separately. The associations between LBD, blood cholesterol levels, and fasting glucose levels were assessed using multiple binary logistic regression analyses adjusted for multiple covariates.

RESULTS

Increased plasma LDL-C levels and lower HDL-C levels were independently associated with the risk of LBD in models adjusted for age, sex, education, alcohol use status, smoking status, and vascular disorders. Higher fasting glucose levels may be associated with the risk of LBD.

CONCLUSION

The results of this study suggest that elevated levels of LDL-C and reduced levels of HDL-C were associated with LBD development and therefore are potential nutritional risk factors for LBD. Adjusting diet and individualized and effective cholesterol-lowering therapy in high-risk adults may aid in the prevention or management of LBD.

The Significance of Oxidized Low-Density Lipoprotein in Body Fluids as a Marker Related to Diseased Conditions

Oxidatively modified low-density lipoprotein (oxLDL) is known to be involved in various diseases, including cardiovascular diseases. The presence of oxLDL in the human circulatory system and in atherosclerotic lesions has been demonstrated using monoclonal antibodies. Studies have shown the significance of circulating oxLDL in various systemic diseases, including acute myocardial infarction and diabetic mellitus. Several different enzyme-linked immunosorbent assay (ELISA) procedures to measure oxLDL were utilized. Evidence has been accumulating that reveals changes in oxLDL levels under certain pathological conditions. Since oxLDL concentration tends to correlate with low-density lipoprotein (LDL)-cholesterol, the ratio of ox-LDL and LDL rather than oxLDL concentration alone has also been focused. In addition to circulating plasma, LDL and oxLDL are found in gingival crevicular fluid (GCF), where the ratio of oxLDL to LDL in GCF is much higher than in plasma. LDL and oxLDL levels in GCF show an increase in diabetic patients and periodontal patients, suggesting that GCF might be useful in examining systemic conditions. GCF oxLDL increased when the teeth were affected by periodontitis. It is likely that oxLDL levels in plasma and GCF could reflect oxidative stress and transfer efficacy in the circulatory system.

Emerging Biomarkers in Vascular Cognitive Impairment and Dementia: From Pathophysiological Pathways to Clinical Application

Vascular pathology is the second most common neuropathology of dementia after Alzheimer’s disease (AD), with small vessels disease (SVD) being considered the major cause of vascular cognitive impairment and dementia (VCID). This review aims to evaluate pathophysiological pathways underlying a diagnosis of VCID. Firstly, we will discuss the role of endothelial dysfunction, blood-brain barrier disruption and neuroinflammation in its pathogenesis. Then, we will analyse different biomarkers including the ones of inflammatory responses to central nervous system tissue injuries, of coagulation and thrombosis and of circulating microRNA. Evidences on peripheral biomarkers for VCID are still poor and large-scale, prospectively designed studies are needed to translate these findings into clinical practice, in order to set different combinations of biomarkers to use for differential diagnosis among types of dementia.

Association between serum cholesterol levels and Alzheimer's disease in China: a case-control study

To examine the association between blood cholesterol concentrations and Alzheimer's disease (AD) in the Chinese elderly. A case-control study was implemented between November 2011 and November 2017. Elderly patients aged ≥ 55 years with (n = 117) and without AD (control participants; n = 117) were recruited from the Neurology Central Hospital of Tianjin, China. The associations between AD and blood parameters were assessed using multiple binary logistic regression analyses adjusted for multiple covariates. Higher serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) levels and lower serum high-density lipoprotein cholesterol (HDL-C) levels associated with AD risk in the models adjusted for (1) age, sex and education; and (2) further adjusted for body mass index, smoking status, stroke, hypertension, type 2 diabetes mellitus and heart disease. Increased serum TC and LDL-C levels and lower HDL-C levels were independently associated with the risk of AD.

Combined measurement of plasma cystatin C and low-density lipoprotein cholesterol: A valuable tool for evaluating progressive supranuclear palsy

INTRODUCTION

Progressive supranuclear palsy (PSP) was previously thought as a cause of atypical Parkinsonism. Although Cystatin C (Cys C) and low-density cholesterol lipoprotein-C (LDL-C) are known to play critical roles in Parkinsonism, it is unknown whether they can be used as markers to distinguish PSP patients from healthy subjects and to determine disease severity.

METHODS

We conducted a cross-sectional study to determine plasma Cys C/HDL/LDL-C levels of 40 patients with PSP and 40 healthy age-matched controls. An extended battery of motor and neuropsychological tests, including the PSP-Rating Scale (PSPRS), the Non-Motor Symptoms Scale (NMSS), Geriatric Depression Scale (GDS) and Mini-Mental State Examination (MMSE), was used to evaluate the disease severity. Receiver operating characteristic (ROC) curves were adopted to assess the prognostic accuracy of Cys C/LDL-C levels in distinguishing PSP from healthy subjects.

RESULTS

Patients with PSP exhibited significantly higher plasma levels of Cys C and lower LDL-C. The levels of plasma Cys C were positively and inversely correlated with the PSPRS/NMSS and MMSE scores, respectively. The LDL-C/HDL-C ratio was positively associated with PSPRS/NMSS and GDS scores. The ROC curve for the combination of Cys C and LDL-C yielded a better accuracy for distinguishing PSP from healthy subjects than the separate curves for each parameter.

CONCLUSIONS

Plasma Cys C and LDL-C may be valuable screening tools for differentiating PSP from healthy subjects; while they could be useful for the PSP intensifies and severity evaluation. A better understanding of Cys C and LDL-C may yield insights into the pathogenesis of PSP.

Oxidized LDL at the crossroads of immunity in non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is viewed as the hepatic manifestation of the metabolic syndrome and is a condition hallmarked by lipid accumulation in the liver (steatosis) along with inflammation (hepatitis). Currently, the etiology and mechanisms leading to obesity-induced hepatic inflammation are not clear and, as a consequence, strategies to diagnose or treat NASH in an accurate manner do not exist. In the current review, we put forward the concept of oxidized lipids as a significant risk factor for NASH. We will focus on the contribution of the different types of oxidized lipids as part of the oxidized low-density lipoprotein (oxLDL) to the hepatic inflammatory response. Furthermore, we will elaborate on the underlying mechanisms linking oxLDL to inflammatory responses in the liver and on how these cascades can be used as therapeutic targets to combat NASH. This article is part of a Special Issue entitled: Lipid modification and lipid peroxidation products in innate immunity and inflammation edited by Christoph J. Binder.

Reprint of: Microglial toll-like receptors and Alzheimer's disease

Microglial activation represents an important pathological hallmark of Alzheimer's disease (AD), and emerging data highlight the involvement of microglial toll-like receptors (TLRs) in the course of AD. TLRs have been observed to exert both beneficial and detrimental effects on AD-related pathologies, and transgenic animal models have provided direct and credible evidence for an association between TLRs and AD. Moreover, analyses of genetic polymorphisms have suggested interactions between genetic polymorphisms in TLRs and AD risk, further supporting the hypothesis that TLRs are involved in AD. In this review, we summarize the key evidence in this field. Future studies should focus on exploring the mechanisms underlying the potential roles of TLRs in AD.

Microglial toll-like receptors and Alzheimer's disease

Microglial activation represents an important pathological hallmark of Alzheimer's disease (AD), and emerging data highlight the involvement of microglial toll-like receptors (TLRs) in the course of AD. TLRs have been observed to exert both beneficial and detrimental effects on AD-related pathologies, and transgenic animal models have provided direct and credible evidence for an association between TLRs and AD. Moreover, analyses of genetic polymorphisms have suggested interactions between genetic polymorphisms in TLRs and AD risk, further supporting the hypothesis that TLRs are involved in AD. In this review, we summarize the key evidence in this field. Future studies should focus on exploring the mechanisms underlying the potential roles of TLRs in AD.