End products of lipid peroxidation in erythrocyte membranes in Alzheimer's disease

Blood-Based Biomarkers for Alzheimer's Disease Diagnosis and Progression: An Overview

Alzheimer’s Disease (AD) is a progressive neurodegenerative disease characterized by amyloid-β (Aβ) plaque deposition and neurofibrillary tangle accumulation in the brain. Although several studies have been conducted to unravel the complex and interconnected pathophysiology of AD, clinical trial failure rates have been high, and no disease-modifying therapies are presently available. Fluid biomarker discovery for AD is a rapidly expanding field of research aimed at anticipating disease diagnosis and following disease progression over time. Currently, Aβ_1–42, phosphorylated tau, and total tau levels in the cerebrospinal fluid are the best-studied fluid biomarkers for AD, but the need for novel, cheap, less-invasive, easily detectable, and more-accessible markers has recently led to the search for new blood-based molecules. However, despite considerable research activity, a comprehensive and up-to-date overview of the main blood-based biomarker candidates is still lacking. In this narrative review, we discuss the role of proteins, lipids, metabolites, oxidative-stress-related molecules, and cytokines as possible disease biomarkers. Furthermore, we highlight the potential of the emerging miRNAs and long non-coding RNAs (lncRNAs) as diagnostic tools, and we briefly present the role of vitamins and gut-microbiome-related molecules as novel candidates for AD detection and monitoring, thus offering new insights into the diagnosis and progression of this devastating disease.

Association Between Oxidative Stress and Altered Cholesterol Metabolism in Alzheimer's Disease Patients

BACKGROUND

Oxidative stress is the main feature of several diseases including Alzheimer's disease (AD). The involvement of oxysterols derivates has been recently reported.

OBJECTIVE

The aim of this study was to evaluate the implication of oxidative stress in cholesterol impairment in AD patients.

METHODS

A case-control study was conducted on 56 AD patients and 97 controls. Levels of oxidative biomarkers, including lipid peroxidation products and antioxidant enzyme activities were measured with spectrophotometric methods on red blood cells (RBCs) and plasma. Cholesterol precursors and oxysterols (7-Ketocholeterol (7KC), 7α-hydroxycholesterol (7α-OHC), 7β-hydroxycholesterol (7β-OHC), 24Shydroxycholesterol (24S-OH), 25-hyroxycholesterol (25-OHC), and 27-hydroxycholesterol (27-OHC), in plasma were quantified by gas chromatography coupled with mass spectrometry.

RESULTS

In RBCs and plasma of AD patients, a significant decrease of glutathione peroxidase (GPx) activity was detected associated with raised levels of malondialdehyde (MDA). A decreased level of lanosterol and an accumulation of 7β-OHC, 24S-OHC, 27-OHC, and 25-OHC that were higher in plasma of AD patients, compared to controls, were also observed in AD patients. Mini-Mental State Examination (MMSE) score was correlated with MDA and conjugated dienes (CD) levels in plasma. Besides, the MDA level in RBCs was correlated with 7β-OHC. Binary logistic regression revealed an association between GPx activity and AD (OR=0.895, 95%CI: 0.848-0.945. P<0.001).

CONCLUSION

Our data consolidate the relationship between the rupture of redox homeostasis and lipid and cholesterol oxidation in AD.

A Novel Quantitative Method for the Detection of Lipofuscin, the Main By-Product of Cellular Senescence, in Fluids

Lipofuscin accumulation is a hallmark of senescence. This nondegradable material aggregates in the cytoplasm of stressed or damaged cells due to metabolic imbalance associated with aging and age-related diseases. Indications of a soluble state of lipofuscin have also been provided, rendering the perspective of monitoring such processes via lipofuscin quantification in liquids intriguing. Therefore, the development of an accurate and reliable method is of paramount importance. Currently available assays are characterized by inherent pitfalls which demote their credibility. We herein describe a simple, highly specific and sensitive protocol for measuring lipofuscin levels in any type of liquid. The current method represents an evolution of a previously described assay, developed for in vitro and in vivo senescent cell recognition that exploits a newly synthesized Sudan Black-B analog (GL13). Analysis of human clinical samples with the modified protocol provided strong evidence of its usefulness for the exposure and surveillance of age-related conditions.

Effects of porcine brain hydrolysate on impairment of cognitive learning ability in amyloid β(1-40) -infused rats

This study assessed whether administering porcine brain hydrolysate (PBH) ameliorates the impairment of spatial cognition learning ability in amyloid β (Aβ)-infused rats. PBH was prepared using organic solvents (i.e., acetone and ethanol). Enzyme hydrolysates were derived from these PBH and the sequence of the Aβ peptide for infusion was selected. The results indicated the PBH, in particular EP (porcine brain extract with ethanol and protease N), demonstrated the potentials to reduce damage of neurodegenerative disorders in vitro and in vivo. The principal findings of this study indicate that PBH has prolyl endopeptidase inhibitory activity in vitro. Moreover, administering EP to Aβ(1-40)-infused rats significantly improves their performance on reference, spatial performance, and working memory tests during water maze tasks; concurrent proportional decreases are also observed in malondialdehyde levels, acetylcholinesterase (AChE) activity, and Aβ accumulation levels in brain tissues. The PBH was suggested to ameliorate learning deficits associated with Alzheimer's disease by inhibition of lipid peroxidation in the brain of Aβ infused rat.

Mitochondrial dysfunction - Silent killer in cerebral ischemia

Mitochondrial dysfunction aggravates ischemic neuronal injury through activation of various pathophysiological and molecular mechanisms. Ischemic neuronal injury is particularly intensified during reperfusion due to impairment of mitochondrial function. Mitochondrial mutilation instigates alterations in calcium homeostasis in neurons, which plays a pivotal role in the maintenance of normal neuronal function. Increase in intracellular calcium level in mitochondria triggers the opening of mitochondrial transition pore and over production of reactive oxygen species (ROS). Several investigations have concluded that ROS not only contribute to lipids and proteins damage, but also transduce apoptotic signals leading to neuronal death. In addition to the above mentioned reasons, endoplasmic reticulum (ER) stress due to excitotoxicity also leads to neuronal death. Recently, some newer proteins have been claimed to induce "mitophagy" by triggering the receptors on autophagic membranes leading to neurodegeneration. This review summarizes the mechanisms underlying neuronal death involving mitochondrial dysfunction and mitophagy.

Erythrocyte membrane stability to hydrogen peroxide is decreased in Alzheimer disease

The brain and erythrocytes have similar susceptibility toward free radicals. Therefore, erythrocyte abnormalities might indicate the progression of the oxidative damage in Alzheimer disease (AD). The aim of this study was to investigate erythrocyte membrane stability and plasma antioxidant status in AD. Fasting blood samples (from 17 patients with AD and 14 healthy controls) were obtained and erythrocyte membrane stability against hydrogen peroxide and 2,2'-azobis-(2-amidinopropane) dihydrochloride (AAPH), serum Trolox equivalent antioxidant capacity (TEAC), residual antioxidant activity or gap (GAP), erythrocyte catalase activity (CAT), erythrocyte superoxide dismutase (SOD) activity, erythrocyte nonproteic thiols, and total plasma thiols were determined. A significant decrease in erythrocyte membrane stability to hydrogen peroxide was found in AD patients when compared with controls (P<0.05). On the contrary, CAT activity (P<0.0001) and total plasma thiols (P<0.05) were increased in patients with AD compared with controls. Our results indicate that the most satisfactory measurement of the oxidative stress level in the blood of patients with AD is the erythrocyte membrane stability to hydrogen peroxide. Reduced erythrocyte membrane stability may be further evaluated as a potential peripheral marker for oxidative damage in AD.

Oxidative Stress and Erythrocyte Membrane Alterations in Children with Autism: Correlation with Clinical Features

It has been suggested that oxidative stress may play a role in the pathogenesis of Autism Spectrum Disorders (ASD), but the literature reports somewhat contradictory results. To further investigate the issue, we evaluated a high number of peripheral oxidative stress parameters, and some related issues such as erythrocyte membrane functional features and lipid composition. Twenty-one autistic children (Au) aged 5 to 12 years, were gender and age-matched with 20 typically developing children (TD). Erythrocyte thiobarbituric acid reactive substances, urinary isoprostane and hexanoyl-lysine adduct levels were elevated in Au, thus confirming the occurrence of an imbalance of the redox status of Au, whilst other oxidative stress markers or associated parameters (urinary 8-oxo-dG, plasma radical absorbance capacity and carbonyl groups, erythrocyte superoxide dismutase and catalase activities) were unchanged. A very significant reduction of Na⁺/K⁺-ATPase activity (−66%, p<0.0001), a reduction of erythrocyte membrane fluidity and alteration in erythrocyte fatty acid membrane profile (increase in monounsaturated fatty acids, decrease in EPA and DHA-ω3 with a consequent increase in ω6/ω3 ratio) were found in Au compared to TD, without change in membrane sialic acid content. Some Au clinical features appear to be correlated with these findings; in particular, hyperactivity score appears to be related with some parameters of the lipidomic profile and membrane fluidity. Oxidative stress and erythrocyte membrane alterations may play a role in the pathogenesis of ASD and prompt the development of palliative therapeutic protocols. Moreover, the marked decrease in NKA could be potentially utilized as a peripheral biomarker of ASD.

Triggers and effectors of oxidative stress at blood-brain barrier level: relevance for brain ageing and neurodegeneration

As fundamental research advances, it is becoming increasingly clear that a clinically expressed disease implies a mixture of intertwining molecular disturbances. Oxidative stress is one of such pathogenic pathways involved in virtually all central nervous system pathologies, infectious, inflammatory, or degenerative in nature. Since brain homeostasis largely depends on integrity of blood-brain barrier (BBB), many studies focused lately on BBB alteration in a wide spectrum of brain diseases. The proper two-way molecular transfer through BBB depends on several factors, including the functional status of its tight junction (TJ) complexes of proteins sealing neighbour endothelial cells. Although there is abundant experimental work showing that oxidative stress associates BBB permeability alteration, less is known about its implications, at molecular level, in TJ protein expression or TJ-related cell signalling. In this paper, oxidative stress is presented as a common pathway for different brain pathogenic mechanisms which lead to BBB dysregulation. We revise here oxidative-induced molecular mechanisms of BBB disruption and TJ protein expression alteration, in relation to ageing and neurodegeneration.