Oxidized LDL lipids increase β-amyloid production by SH-SY5Y cells through glutathione depletion and lipid raft formation

Alzheimer's Disease: A Review of Pathology, Current Treatments, and the Potential Therapeutic Effect of Decreasing Oxidative Stress by Combined Vitamin D and l-Cysteine Supplementation

Significance: Excess oxidative stress and neuroinflammation are risk factors in the onset and progression of Alzheimer's disease (AD) and its association with amyloid-β plaque accumulation. Oxidative stress impairs acetylcholine (ACH) and N-methyl-d-aspartate receptor signaling in brain areas that function in memory and learning. Glutathione (GSH) antioxidant depletion positively correlates with the cognitive decline in AD subjects. Treatments that upregulate GSH and ACH levels, which simultaneously decrease oxidative stress and inflammation, may be beneficial for AD. Recent Advances: Some clinical trials have shown a benefit of monotherapy with vitamin D (VD), whose deficiency is linked to AD or with l-cysteine (LC), a precursor of GSH biosynthesis, in reducing mild cognitive impairment. Animal studies have shown a simultaneous decrease in ACH esterase (AChE) and increase in GSH; combined supplementation with VD and LC results in a greater decrease in oxidative stress and inflammation, and increase in GSH levels compared with monotherapy with VD or LC. Therefore, cosupplementation with VD and LC has the potential of increasing GSH, downregulation of oxidative stress, and decreased inflammation and AChE levels. Future Directions: Clinical trials are needed to determine whether safe low-cost dietary supplements, using combined VD+LC, have the potential to alleviate elevated AChE, oxidative stress, and inflammation levels, thereby halting the onset of AD. Goal of Review: The goal of this review is to highlight the pathological hallmarks and current Food and Drug Administration-approved treatments for AD, and discuss the potential therapeutic effect that cosupplementation with VD+LC could manifest by increasing GSH levels in patients. Antioxid. Redox Signal. 40, 663-678.

Acid sphingomyelinase as a pathological and therapeutic target in neurological disorders: focus on Alzheimer's disease

Over the past decade, numerous studies have highlighted the importance of acid sphingomyelinase (ASM) in disease treatment in humans. This enzyme functions primarily to generate ceramide, maintain the cellular membrane, and regulate cellular function. However, in the blood and brain of patients with neurological disorders, including major depression, ischemic stroke, amyotrophic lateral sclerosis, multiple sclerosis, and Alzheimer's disease (AD), elevated ASM levels significantly suggest disease onset or progression. In these diseases, increased ASM is profoundly involved in neuronal death, abnormal autophagy, neuroinflammation, blood-brain barrier disruption, hippocampal neurogenesis loss, and immune cell dysfunction. Moreover, genetic and pharmacological inhibition of ASM can prevent or ameliorate various diseases. The therapeutic effects of ASM inhibition have prompted the urgent need to develop ASM inhibitors, and several ASM inhibitors have been identified. In this review, we summarize the current knowledge on the critical roles and mechanisms of ASM in brain cells and blood that are associated with different neuropathological features, especially those observed in AD. Furthermore, we elucidate the potential possibility and limitations of existing ASM-targeting drugs according to experimental studies in neurological disorder mouse models.

Desipramine ameliorates fine particulate matter-induced hepatic insulin resistance by modulating the ceramide metabolism in mice

Recent research has highlighted a correlation between exposure to ambient fine particulate matter (PM2.5) and the development of systemic insulin resistance (IR) along with an elevated risk of diabetes. Ceramide has emerged as one of the pathogenic mechanisms contributing to IR. The inhibition of acid sphingomyelinase (ASMase) activity by desipramine (DES) has been shown to effectively reduce ceramide levels. In the present study, 24 female C57BL/6 N mice were randomized into one of the four groups: the filtered air exposure (FA) group, the concentrated PM2.5 exposure (PM) group, the concentrated PM2.5 treated with low-dose DES (DL) group, and the concentrated PM2.5 treated with high-dose DES (DH) group. The PM, DL and DH groups were exposed to PM2.5 for an 8-week period within a whole-body exposure system. The study encompassed extensive examinations of glucose homeostasis, liver lipid profile, ceramide pathway, and insulin signaling pathway. Our results demonstrated that PM2.5 exposure caused impaired glucose tolerance, elevated ceramide levels, increased phosphorylation PP2A, reduced Akt phosphorylation, and hindered GLUT2 expression. Remarkably, DES administration mitigated PM2.5-induced IR by effectively lowering ceramide levels. In conclusion, the reduction of ceramide levels by DES may be a promising therapeutic strategy for coping PM2.5-induced IR.

Positive association of acetylcholinesterase (AChE) with the neutrophil-to-lymphocyte ratio and HbA1c, and a negative association with hydrogen sulfide (H2S) levels among healthy African Americans, and H2S-inhibition and high-glucose-upregulation of AChE in cultured THP-1 human monocytes

The incidence of Alzheimer's disease (AD) is higher in people over the age of 65 and in African Americans (AA). Elevated acetylcholinesterase (AChE) activity has been considered a major player in the onset of AD symptoms. As a result, many FDA-approved AD drugs target AChE inhibition to treat AD patients. Hydrogen sulfide (H2S) is a signaling molecule known to downregulate oxidative stress and inflammation. The neutrophil-to-lymphocyte ratio (NLR) in the blood is widely used as a biomarker to monitor inflammation and immunity. This study examined the hypothesis that plasma AChE levels have a negative association with H2S levels and that a positive association exists between levels of NLR, HbA1c, and ROS with the AChE in the peripheral blood. The fasting blood sample was taken from 114 African Americans who had provided written informed consent approved by the IRB. The effect of H2S and high-glucose treatment on AChE activity levels was also investigated in THP-1 human monocytes. There was a significant negative relationship between AChE and the levels of H2S (r = -0.41, p = 0.001); a positive association between the levels of AChE with age (r = 0.26, p = 0.03), NLR (r = 0.23, p = 0.04), ROS (r = 0.23, p = 0.04) and HbA1c levels (r = 0.24, p = 0.04), in AA subjects. No correlation was seen between blood levels of AChE and acetylcholine (ACh). Blood creatinine had a negative correlation (r = -0.23, p = 0.04) with ACh levels. There was a significant effect of H2S on AChE inhibition and of high glucose in upregulating AChE activity in cultured monocytes. This study suggests hyperglycemia and lower H2S status can contribute to an increase in the AChE activity levels. Future clinical studies are needed to examine the potential benefits of supplementation with hydrogen sulfide pro-drugs/compounds in reducing the AChE and the cognitive dysfunctions associated with AD.

Glycerophospholipid Analysis of Optic Nerve Regeneration Models Indicate Potential Membrane Order Changes Associated with the Lipidomic Shifts

Purpose: Optic nerve (ON) injury causes irreversible degeneration, leading to vision loss that cannot be restored with available therapeutics. Current therapies slow further degeneration but do not promote regeneration. New regenerative factors have been discovered that are successful in vivo. However, the mechanisms of efficient long-distance regeneration are still unknown. Membrane expansion by lipid insertion is an essential regenerative process, so lipid profiles for regenerating axons can provide insight into growth mechanisms. This article's analysis aims to add to the increasingly available ON regeneration lipid profiles and relate it to membrane order/properties. Methods: In this study, we present an analysis of glycerophospholipids, one of the largest axonal lipid groups, from three mammalian ON regeneration lipid profiles: Wnt3a, Zymosan + CPT-cAMP, and Phosphatase/Tensin homolog knockout (PTENKO) at 7 and 14 days post crush (dpc). Significant lipid classes, species, and ontological properties were crossreferenced between treatments and analyzed using Metaboanalyst 5.0 and Lipid Ontology (LION). Membrane order changes associated with significant lipid classes were evaluated by C-Laurdan dye and exogenous lipids provided to a neuroblastoma cell line. Results and Conclusions: At 7 dpc, ONs show increased lysoglycerophospholipids and decreased phosphatidylethanolamines (PEs)/negative intrinsic curvature lipids. At 14 dpc, regenerative treatments show divergence: Wnt3a displays higher lysoglycerophospholipid content, while Zymosan and PTENKO decrease lysoglycerophospholipids and increase phosphatidylcholine (PC)-related species. Membrane order imaging indicates lysoglycerophospholipids decreases membrane order while PE and PC had no significant membrane order effects. Understanding these changes will allow therapeutic development targeting lipid metabolic pathways that can be used for vision loss treatments.

Antioxidant potentials of furanodihydrobenzoxanthones from Artocarpus elasticus and their protection against oxLDL induced injury in SH-SY5Y cells

Exposure to reactive oxygen species (ROS) leads to the oxidation of low-density lipoproteins (LDL), converting them into oxidized ones (oxLDL), which are involved in the pathogenesis of Alzheimer's disease, suggesting a potential link between lipid dysregulation and neurodegenerative processes. Phenolic metabolites derived from Artocarpus elasticus root bark were found to possess significant antioxidant properties at three different radical scavenging assays, including 2,2-diphenyl-1-picrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC), and thiobarbituric acid reactive substances (TBARS). Among them, furanodihydrobenzoxanthones (1-3) demonstrated notable protection against Cu2+ induced LDL oxidation, with IC50 values ranging from 0.9 to 2.9 μM in measurement of the malondialdehyde (MDA) production at TBARS and prolonged lag times (>180 min) in the generation of conjugated diene (CD). At a concentration of 10 μM, all three compounds (1-3) effectively protected against LDL oxidation as determined by relative electrophoretic mobility (REM). The most potent compound 1 defended human neuroblastoma SH-SY5Y cells from oxLDL-mediated dysfunction, including oxLDL-induced cytotoxicity, inhibited reactive oxygen species (ROS) formation, and enhancing mitochondrial membrane potential (ΔΨm). Individual components annotation in the ethylacetate extract was performed using LC-ESI-QTOF/MS, which serves as a chemotaxonomic marker for A. elasticus root barks.

Design of Smart Aggregates: Toward Rapid Clinical Diagnosis of Hyperlipidemia in Human Blood

Molecular aggregates with environmental responsive properties are desired for their wide practical applications such as bioprobes. Here, a series of smart near-infrared (NIR) luminogens for hyperlipidemia (HLP) diagnosis is reported. The aggregates of these molecules exhibit a twisted intramolecular charge-transfer effect in aqueous media, but aggregation-induced emission in highly viscous media due to the restriction of the intramolecular motion. These aggregates, which can autonomously respond to different environments via switching the aggregation state without changing their chemical structures are described, as "smart aggregates". Intriguingly, these luminogens demonstrate NIR-II and NIR-III luminescence with ultralarge Stokes shifts (>950 nm). Both in vitro detection and in vivo imaging of HLP can be realized in a mouse model. Linear relationships exist between the emission intensity and multiple pathological parameters in blood samples of HLP patients. Thus, the design of smart aggregate facilitates rapid and accurate detection of HLP and provides a promising attempt in aggregate science.

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

Background:

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

Objective:

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

Methods:

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

Results:

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

Conclusion:

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

Influential role of 7-Ketocholesterol in the progression of Alzheimer's disease

Millions of people are affected by neurodegenerative diseases worldwide. They occur due to the loss of brain functions or peripheral nervous system dysfunction. If untreated, prolonged condition ultimately leads to death. Mostly they are associated with stress, altered cholesterol metabolism, inflammation and organelle dysfunction. Endogenous cholesterol and phospholipids in brain undergo auto-oxidation by enzymatic as well as non-enzymatic modes leading to the formation of by-products such as 4-hydroxynonenal and oxysterols. Among various oxysterols, 7-ketocholesterol (7KCh) is one of the major toxic components involved in altering neuronal lipid metabolism, contributing to inflammation and nerve cell damage. More evidently 7KCh is proven to induce oxidative stress and affects membrane permeability. Loss in mitochondrial membrane potential affects metabolism of cell organelles such as lysosomes and peroxisomes which are involved in lipid and protein homeostasis. This in turn could affect amyloidogenesis, tau protein phosphorylation and accumulation in pathological conditions of neurodegenerative diseases. Lipid alterations and the consequent pathogenic protein accumulation, results in the damage of cell organelles and microglial cells. This could be a reason behind disease progression and predominantly reported characteristics of neurodegenerative disorders such as Alzheimer's disease. This review focuses on the role of 7KCh mediated neurodegenerative Alzheimer's disease with emphasis on alterations in the lipid raft microdomain. In addition, current trends in the significant therapies related to 7KCh inhibition are highlighted.

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

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

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

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Oxidative distress is strongly linked to neurodegeneration.

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Consumption and levels of carotenoids are linked to cognitive frailty.

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

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

Cerebrospinal Fluid 7-Ketocholesterol Level is Associated with Amyloid-β42 and White Matter Microstructure in Cognitively Healthy Adults

BACKGROUND

Abnormal cholesterol metabolism changes the neuronal membrane and may promote amyloidogenesis. Oxysterols in cerebrospinal fluid (CSF) are related to Alzheimer's disease (AD) biomarkers in mild cognitive impairment and dementia. Cholesterol turnover is important for axonal and white matter (WM) microstructure maintenance.

OBJECTIVE

We aim to demonstrate that the association of oxysterols, AD biomarkers, and WM microstructure occurs early in asymptomatic individuals.

METHODS

We studied the association of inter-individual variability of CSF 24-hydroxycholesterol (24-OHC), 27-hydroxycholesterol (27-OHC), 7-ketocholesterol (7-KC), 7β-hydroxycholesterol (7β-OHC), amyloid-β42 (Aβ42), total-tau (t-tau), phosphorylated-tau (p-tau), neurofilament (NfL), and WM microstructure using diffusion tensor imaging, generalized linear models and moderation/mediation analyses in 153 healthy adults.

RESULTS

Higher 7-KC levels were related to lower Aβ42, indicative of greater AD pathology (p = 0.041) .  Higher 7-KC levels were related to lower fractional anisotropy (FA) and higher mean (MD), axial (AxD), and radial (RD) diffusivity. 7-KC modulated the association between AxD and NfL in the corpus callosum splenium (B = 39.39, p = 0.017), genu (B = 68.64, p = 0.000), and fornix (B = 10.97, p = 0.000). Lower Aβ42 levels were associated to lower FA and higher MD, AxD, and RD in the fornix, corpus callosum, inferior longitudinal fasciculus, and hippocampus. The association between AxD and Aβ42 was moderated by 7K-C (p = 0.048).

CONCLUSION

This study adds clinical evidence to support the role of 7K-C on axonal integrity and the involvement of cholesterol metabolism in the Aβ42 generation process.

Cellular compartments challenged by membrane photo-oxidation

The lipid composition impacts directly on the structure and function of the cytoplasmic as well as organelle membranes. Depending on the type of membrane, specific lipids are required to accommodate, intercalate, or pack membrane proteins to the proper functioning of the cells/organelles. Rather than being only a physical barrier that separates the inner from the outer spaces, membranes are responsible for many biochemical events such as cell-to-cell communication, protein-lipid interaction, intracellular signaling, and energy storage. Photochemical reactions occur naturally in many biological membranes and are responsible for diverse processes such as photosynthesis and vision/phototaxis. However, excessive exposure to light in the presence of absorbing molecules produces excited states and other oxidant species that may cause cell aging/death, mutations and innumerable diseases including cancer. At the same time, targeting key compartments of diseased cells with light can be a promising strategy to treat many diseases in a clinical procedure called Photodynamic Therapy. Here we analyze the relationships between membrane alterations induced by photo-oxidation and the biochemical responses in mammalian cells. We specifically address the impact of photosensitization reactions in membranes of different organelles such as mitochondria, lysosome, endoplasmic reticulum, and plasma membrane, and the subsequent responses of eukaryotic cells.

TPGS2k-PLGA composite nanoparticles by depleting lipid rafts in colon cancer cells for overcoming drug resistance

Recently, studies showed that the drug-resistant cell membranes have formed high-density lipid rafts regions; traditional targeted drug delivery systems can hardly break through the hard shell and deliver drugs to drug-resistant cells. Here, α-tocopherol polyethylene glycol 2000 succinate (TPGS_2k) was successfully synthesized and used to modify poly (lactic-glycolic acid) nanoparticles co-loaded with doxorubicin (DOX) and simvastatin (SV) (SV/DOX@TPGS_2k-PLGA NPs). The purpose of this study is to explore the synergistic effect between SV consuming cholesterol in lipid rafts and directly down-regulating P-gp expression on the intracellular drugs retention. The research highlights these nanoparticles interrupted lipid rafts (cholesterol-rich domains, where P-gp is often located), which inhibited drug efflux by down-regulating P-gp, promoted the mitochondria apoptosis and made SW620/AD300 cells (DOX-resistant colon cancer cell line) re-sensitized to DOX. Therefore, the carrier can become a promising SV-based nano-delivery system with depleting cholesterol in lipid rafts to reverse drug resistance.

Inflammation, Lipid (Per)oxidation, and Redox Regulation

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

Distribution of plasma oxidised phosphatidylcholines in chronic kidney disease and periodontitis as a co-morbidity

Individuals with chronic kidney disease (CKD) and periodontitis as a co-morbidity have a higher mortality rate than individuals with CKD and no periodontitis. The inflammatory burden associated with both diseases contributes to an increased risk of cardiovascular and all-cause mortality. We previously demonstrated that periodontitis is associated with increasing circulating markers of inflammation and oxidative stress. We propose that inflammatory oxidised phosphocholines may contribute to the increased risk of cardiovascular disease in patients with CKD. However, the analysis of oxidised phospholipids has been limited by a lack of authentic standards for absolute quantification. Here, we have developed a comprehensive quantification liquid chromatography-mass spectrometry-based multiple reaction monitoring method for oxidised phospholipids (including some without available authentic species) that enables us to simultaneously measure twelve oxidised phosphatidylcholine species with high levels of sensitivity and specificity. The standard curves for commercial standards 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphatidylcholine (PGPC); 1-palmitoyl-2-(9'-oxo-nonanoyl)-sn-glycero-3-phosphatidylcholine (PONPC), 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphatidylcholine (PAzPC) and 1-palmitoyl-2-(5'-oxo-valeroyl)-sn-glycero-3-phosphatidylcholine (POVPC), were linear with a correlation coefficient greater than 0.99 for all analytes. The method is reproducible, with intra- and inter-day precision <15%, and accuracy within ±5% of nominal values for all analytes. This method has been successfully applied to investigate oxidised phosphatidylcholine in plasma from CKD patients with and without chronic periodontitis and the data that was obtained has been compared to plasma from healthy controls. Comparative analysis demonstrates altered chain fragmented phosphatidylcholine profiles in the plasma samples of patients with CKD and periodontitis as a co-morbidity compared to healthy controls.

Dietary Polyphenols: A Multifactorial Strategy to Target Alzheimer's Disease

Ageing is an inevitable fundamental process for people and is their greatest risk factor for neurodegenerative disease. The ageing processes bring changes in cells that can drive the organisms to experience loss of nutrient sensing, disrupted cellular functions, increased oxidative stress, loss of cellular homeostasis, genomic instability, accumulation of misfolded protein, impaired cellular defenses and telomere shortening. Perturbation of these vital cellular processes in neuronal cells can lead to life threatening neurological disorders like Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Lewy body dementia, etc. Alzheimer's Disease is the most frequent cause of deaths in the elderly population. Various therapeutic molecules have been designed to overcome the social, economic and health care burden caused by Alzheimer's Disease. Almost all the chemical compounds in clinical practice have been found to treat symptoms only limiting them to palliative care. The reason behind such imperfect drugs may result from the inefficiencies of the current drugs to target the cause of the disease. Here, we review the potential role of antioxidant polyphenolic compounds that could possibly be the most effective preventative strategy against Alzheimer's Disease.

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

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

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

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

27-hydroxycholesterol promotes Aβ accumulation via altering Aβ metabolism in mild cognitive impairment patients and APP/PS1 mice

The oxysterol 27-hydroxycholesterol (27-OHC) has been considered to play a key role in the pathogenesis of Alzheimer's disease (AD). Because β-amyloid peptide (Aβ) is the pathological hallmark of AD, the aim of this study is to verify whether 27-OHC could lead to cognitive impairment through modulating Aβ accumulation and deposition. Regulation of Aβ metabolism was explored as the pathogenic mechanism of 27-OHC. Furthermore, microRNAs (miRNAs) and their relations with 27-OHC were also detected. In present study, matched case-control study and APP/PS1 transgenic mice research were conducted. The results showed that the 27-OHC and Aβ in plasma were increased in mild cognitive impairment patients, and a slight correlation was found between 27-OHC and Aβ1-40. This relationship was also proved by the research of APP/PS1 mice. More severe learning and memory impairment and higher Aβ1-40 expression in brain and plasma were detected in the APP/PS1 mice of 27-OHC treatment group. In addition, increased amyloid plaques were also found in the hippocampus of 27-OHC-treated mice. In order to find out the mechanism of 27-OHC on regulating Aβ metabolism, the factors of Aβ production (APP, BACE1 and ADAM10), transport (LRP1 and RAGE) and elimination (NEP and IDE) were tested respectively. The gene and protein expressions of APP, BACE1 and RAGE were increased while LRP1 and IDE were decreased in the brain of 27-OHC-treated mice. At last, down-regulated expression of miRNA let-7g-5p was found after 27-OHC treatment. In conclusion, these findings suggested that excessive 27-OHC could enhance the accumulation and deposition of Aβ both in brain and blood, resulting in a severe impairment of cognition, especially in the modulation of Aβ1-40. The mechanism might be associated with the regulation of Aβ metabolism, and miRNA let-7g-5p was likely to play a vital role in this pathological process induced by 27-OHC.

Contrasting roles of oxidized lipids in modulating membrane microdomains

Lipid rafts display a lateral heterogeneity forming membrane microdomains that hold a fundamental role on biological membranes and are indispensable to physiological functions of cells. Oxidative stress in cellular environments may cause lipid oxidation, changing membrane composition and organization, thus implying in effects in cell signaling and even loss of homeostasis. The individual contribution of oxidized lipid species to the formation or disruption of lipid rafts in membranes still remains unknown. Here, we investigate the role of different structures of oxidized phospholipids on rafts microdomains by carefully controlling the membrane composition. Our experimental approach based on fluorescence microscopy of giant unilamellar vesicles (GUV) enables the direct visualization of the impact of hydroperoxidized POPC lipid (referred to as POPCOOH) and shortened chain lipid PazePC (1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine) on phase separation. We found that the molecular structure of oxidized lipid is of paramount importance on lipid mixing and/or demixing. The hydrophobic mismatch promoted by POPCOOH coupled to its cylindrical molecular shape favor microdomains formation. In contrast, the conical shape of PazePC causes disarrangement of lipid 2D organized platforms. Our findings contribute to better unraveling how oxidized phospholipids can trigger formation or disruption of lipid rafts. As a consequence, phospholipid oxidation may indirectly affect association or dissociation of key biomolecules in the rafts thus altering cell signaling and homeostasis.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Quantitative Systems Pharmacology Model for Alzheimer Disease Indicates Targeting Sphingolipid Dysregulation as Potential Treatment Option

Alzheimer disease (AD) is a devastating neurodegenerative disorder with high unmet medical need. Drug development is hampered by limited understanding of the disease and its driving factors. Quantitative Systems Pharmacology (QSP) modeling provides a comprehensive quantitative framework to evaluate the relevance of biological mechanisms in the context of disease and to predict the efficacy of novel treatments. Here, we report a QSP model for AD with a particular focus on investigating the relevance of dysregulation of cholesterol and sphingolipids. We show that our model captures the modulation of several biomarkers in subjects with AD, as well as the response to pharmacological interventions. We evaluate the impact of targeting the sphingosine-1-phosphate 5 receptor (S1PR5) as a potential novel treatment option for AD, and model predictions increase our confidence in this novel disease pathway. Future applications for the QSP model are in validation of further targets and identification of potential treatment response biomarkers.

Autotaxin⁻Lysophosphatidic Acid Signaling in Alzheimer's Disease

The brain contains various forms of lipids that are important for maintaining its structural integrity and regulating various signaling cascades. Autotaxin (ATX) is an ecto-nucleotide pyrophosphatase/phosphodiesterase-2 enzyme that hydrolyzes extracellular lysophospholipids into the lipid mediator lysophosphatidic acid (LPA). LPA is a major bioactive lipid which acts through G protein-coupled receptors (GPCRs) and plays an important role in mediating cellular signaling processes. The majority of synthesized LPA is derived from membrane phospholipids through the action of the secreted enzyme ATX. Both ATX and LPA are highly expressed in the central nervous system. Dysfunctional expression and activity of ATX with associated changes in LPA signaling have recently been implicated in the pathogenesis of Alzheimer’s disease (AD). This review focuses on the current understanding of LPA signaling, with emphasis on the importance of the autotaxin–lysophosphatidic acid (ATX–LPA) pathway and its alterations in AD and a brief note on future therapeutic applications based on ATX–LPA signaling.

Simvastatin reduces circulating oxysterol levels in men with hypercholesterolaemia

Oxysterols (OHC) are biologically active cholesterol metabolites circulating in plasma that may be formed enzymatically (e.g. 24S-OHC, 25-OHC and 27-OHC) or by autoxidative mechanisms (e.g. 7-ketocholesterol, 7β-OHC and 25-OHC). Oxysterols are more soluble than cholesterol and are reported to exert inflammatory, cytoprotective and apoptotic effects according to concentration and species. Esterified oxysterols have been analysed in people with dementia and cardiovascular diseases although there is no consistent relationship between oxysterol esters and disease. However, oxysterol esters are held in lipoprotein core and may not relate to the concentration and activity of plasma free oxysterols. Methodological limitations have challenged the analysis of free oxysterols to date. We have developed a fast, sensitive and specific quantitative LC-MS/MS, multiple reaction monitoring (MRM) method to target five oxysterols in human plasma with analyte recoveries between 72% and 82% and sensitivities between 5 and 135 pg/ml. A novel method was used to investigate the hypothesis that simvastatin may reduce the concentrations of specific plasma free oxysterols in hypercholesterolaemia. Twenty healthy male volunteers were recruited (aged 41-63 years); ten were asymptomatic with high plasma cholesterol > 6.5 mM and ten were healthy with normal plasma cholesterol (< 6.5 mM). Simvastatin (40 mg/day) was prescribed to those with hypercholesterolaemia. Plasma samples were taken from both groups at baseline and after three months. Simvastatin reduced plasma cholesterol by ~35% (p < 0.05) at the end of three months. Oxysterols generated by autoxidation (but not enzymatically) were elevated up to 45 fold in hypercholesterolaemic midlife men. Plasma oxysterols were restored to those of healthy controls after simvastatin intervention suggesting that autoxidation is either prevented by simvastatin directly or that autoxidation is less prevalent when plasma cholesterol concentrations are within the normal range.

The ROS-mediated activation of IL-6/STAT3 signaling pathway is involved in the 27-hydroxycholesterol-induced cellular senescence in nerve cells

The oxysterol 27-hydroxycholesterol (27HC) is a selective estrogen receptor modulator (SERMs), which like endogenous estrogen 17β-estradiol (E₂) induces the proliferation of ER-positive breast cancer cells in vitro. Interestingly, the observation that 27HC induces adverse effects in neural system, distinguishing it from E₂. It has been suggested that high levels of circulating cholesterol increase the entry of 27HC into the brain, which may induce learning and memory impairment. Based on this evidence, 27HC may be associated with neurodegenerative processes and interrupted cholesterol homeostasis in the brain. However, the biological events that participate in this process remain largely elusive. In the present study, we demonstrated that 27HC induced apparent cellular senescence in nerve cells. Senescence-associated β-galactosidase (SA-β-Gal) assay revealed that 27HC induced senescence in both BV2 cells and PC12 cells. Furthermore, we demonstrated that 27HC promoted the accumulation of cellular reactive oxygen species (ROS) in nerve cells and subsequently activation of IL-6/STAT3 signaling pathway. Notably, treatment with the ROS scavenger N-acetylcysteine (NAC) markedly blocked 27HC-induced ROS production and activation of IL-6/STAT3 signaling pathway. Either blocking the generation of ROS or inhibition of IL-6/STAT3 both attenuated 27HC-induced cellular senescence. In sum, these findings not only suggested a mechanism whereby 27HC induced cellular senescence in nerve cells, but also helped to recognize the 27HC as a novel harmful factor in neurodegenerative diseases.

The Role of Interleukin-18, Oxidative Stress and Metabolic Syndrome in Alzheimer's Disease

The role of interleukins (ILs) and oxidative stress (OS) in precipitating neurodegenerative diseases including sporadic Alzheimer's disease (AD), requires further clarification. In addition to neuropathological hallmarks-extracellular neuritic amyloid-β (Aβ) plaques, neurofibrillary tangles (NFT) containing hyperphosphorylated tau and neuronal loss-chronic inflammation, as well as oxidative and excitotoxic damage, are present in the AD brain. The pathological sequelae and the interaction of these events during the course of AD need further investigation. The brain is particularly sensitive to OS, due to the richness of its peroxidation-sensitive fatty acids, coupled with its high oxygen demand. At the same time, the brain lack robust antioxidant systems. Among the multiple mechanisms and triggers by which OS can accumulate, inflammatory cytokines can sustain oxidative and nitrosative stress, leading eventually to cellular damage. Understanding the consequences of inflammation and OS may clarify the initial events underlying AD, including in interaction with genetic factors. Inflammatory cytokines are potential inducers of aberrant gene expression through transcription factors. Susceptibility disorders for AD, including obesity, type-2 diabetes, cardiovascular diseases and metabolic syndrome have been linked to increases in the proinflammatory cytokine, IL-18, which also regulates multiple AD related proteins. The association of IL-18 with AD and AD-linked medical conditions are reviewed in the article. Such data indicates that an active lifestyle, coupled to a healthy diet can ameliorate inflammation and reduce the risk of sporadic AD.

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

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

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.

LDL-lipids from patients with hypercholesterolaemia and Alzheimer's disease are inflammatory to microvascular endothelial cells: mitigation by statin intervention

Elevated low-density lipoprotein (LDL) concentration in mid-life increases the risk of developing Alzheimer's disease (AD) in later life. Increased oxidized LDL (oxLDL) modification and nitration is observed during dementia and hypercholesterolaemia. We investigated the hypothesis that statin intervention in mid-life mitigates the inflammatory effects of oxLDL on the microvasculature. Human microvascular endothelial cells (HMVECs) were maintained in transwells to mimic the microvasculature and exposed to patient and control LDL. Blood was obtained from statin-naive, normo- and hyper-lipidaemic subjects, AD with vascular dementia (AD-plus) and AD subjects (n=10/group) at baseline. Only hyperlipidaemic subjects with normal cognitive function received 40 mg of simvastatin intervention/day for 3 months. Blood was re-analysed from normo- and hyper-lipidaemic subjects after 3 months. LDL isolated from statin-naive hyperlipidaemic, AD and AD-plus subjects was more oxidized (agarose gel electrophoretic mobility, protein carbonyl content and 8-isoprostane F2α) compared with control subjects. Statin intervention decreased protein carbonyls (2.5±0.4 compared with 3.95±0.2 nmol/mg; P<0.001) and 8-isoprostane F2α (30.4±4.0 pg/ml compared with 43.5±8.42 pg/ml; P<0.05). HMVEC treatment with LDL-lipids (LDL-L) from hyperlipidaemic, AD and AD-plus subjects impaired endothelial tight junction expression and decreased total glutathione levels (AD; 18.61±1.3, AD-plus; 16.5±0.7 nmol/mg of protein) compared with untreated cells (23.8±1.2 compared with nmol/mg of protein). Basolateral interleukin (IL)-6 secretion was increased by LDL-L from hyperlipidaemic (78.4±1.9 pg/ml), AD (63.2±5.9 pg/ml) and AD-plus (80.8±0.9 pg/ml) groups compared with healthy subject lipids (18.6±3.6 pg/ml). LDL-L isolated after statin intervention did not affect endothelial function. In summary, LDL-L from hypercholesterolaemic, AD and AD-plus patients are inflammatory to HMVECs. In vivo intervention with statins reduces the damaging effects of LDL-L on HMVECs.

Association of increased carotid intima-media thickness and lower plasma levels of vitamin C and vitamin E in old age subjects: implications for Alzheimer's disease

In light of the recent advances regarding the role of vascularity in Alzheimer's disease (AD) pathophysiology, the relationship between plasma levels and activities of the major antioxidant molecules and the carotid intima-media thickness (C-IMT) of older persons with no or very mild cognitive impairment was evaluated. The underlying hypothesis is that the IMT may be an indirect index of vascular damage in persons with low levels of plasma antioxidants. Plasma levels of vitamins A, C, E, of uric acid as well as activities of the plasma antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) were measured. Plasma levels of vitamins C and E significantly decreased among participants from the first to the fourth IMT quartile, with a linear slope only for vitamin C. Compared to participants in the lowest vitamin C quartile, the probability to have IMT >1.2 mm significantly decreased among persons from the second to the fourth quartile independent of confounders. In conclusion, only vitamin C plasma levels appear to be selectively associated with the risk of increasing C-IMT. An adequate vitamin C status might be particularly important for protection against AD and other clinical manifestations of vascular and cognitive ageing.

Hypercholesterolaemia-induced oxidative stress at the blood–brain barrier

Blood cholesterol levels are not consistently elevated in subjects with age-related cognitive decline, although epidemiological studies suggest that Alzheimer's disease and cardiovascular diseases share common risk factors. These include the presence of an unusual genetic variant, the APOE4 (apolipoprotein E4) allele, which modulates LDL (low-density lipoproteins) metabolism, increases free radical formation and reduces plasma antioxidant concentrations. Together, these risk factors support a mechanism for increased LDL circulation time and free radical modification of LDL. Plasma oxycholesterols, hydroxylated metabolites of cholesterol, are carried by oxidized LDL, and elevated lipids in mid-life are associated with increased long-term risk of dementia. Although brain cholesterol metabolism is segregated from the systemic circulation, during oxidative stress, plasma oxycholesterols could have damaging effects on BBB (blood–brain barrier) function and consequently on neuronal cells. Cholesterol-lowering drugs such as statins may prevent the modifications to LDL in mid-life and might show beneficial effects in later life.