Alzheimer's disease: genotypes, phenotypes, and treatments

Temporal and regional progression of Alzheimer's disease-like pathology in 3xTg-AD mice

Accumulation of amyloid-β (Aβ) and fibrillary tangles, as well as neuroinflammation and memory loss, are hallmarks of Alzheimer's disease (AD). After almost 15 years from their generation, 3xTg-AD mice are still one of the most used transgenic models of AD. Converging evidence indicates that the phenotype of 3xTg-AD mice has shifted over the years and contradicting reports about onset of pathology or cognitive deficits are apparent in the literature. Here, we assessed Aβ and tau load, neuroinflammation, and cognitive changes in 2-, 6-, 12-, and 20-month-old female 3xTg-AD and nontransgenic (NonTg) mice. We found that ~80% of the mice analyzed had Aβ plaques in the caudal hippocampus at 6 months of age, while 100% of them had Aβ plaques in the hippocampus at 12 months of age. Cortical Aβ plaques were first detected at 12 months of age, including in the entorhinal cortex. Phosphorylated Tau at Ser202/Thr205 and Ser422 was apparent in the hippocampus of 100% of 6-month-old mice, while only 50% of mice showed tau phosphorylation at Thr212/Ser214 at this age. Neuroinflammation was first evident in 6-month-old mice and increased as a function of age. These neuropathological changes were clearly associated with progressive cognitive decline, which was first apparent at 6 months of age and became significantly worse as the mice aged. These data indicate a consistent and predictable progression of the AD-like pathology in female 3xTg-AD mice, and will facilitate the design of future studies using these mice.

Modulating Effect of Diet on Alzheimer's Disease

As life expectancy is growing, neurodegenerative disorders, such as Alzheimer's disease, are increasing. This disease is characterised by the accumulation of intracellular neurofibrillary tangles formed by hyperphosphorylated tau protein, senile plaques composed of an extracellular deposit of β-amyloid peptide (Aβ), and neuronal loss. This is accompanied by deficient mitochondrial function, increased oxidative stress, altered inflammatory response, and autophagy process impairment. The present study gathers scientific evidence that demonstrates that specific nutrients exert a direct effect on both Aβ production and Tau processing and their elimination by autophagy activation. Likewise, certain nutrients can modulate the inflammatory response and the oxidative stress related to the disease. However, the extent to which these effects come with beneficial clinical outcomes remains unclear. Even so, several studies have shown the benefits of the Mediterranean diet on Alzheimer's disease, due to its richness in many of these compounds, to which can be attributed their neuroprotective properties due to the pleiotropic effect they show on the aforementioned processes. These indications highlight the potential role of adequate dietary recommendations for clinical management of both Alzheimer's diagnosed patients and those in risk of developing it, emphasising once again the importance of diet on health.

Decreased CX3CL1 Levels in the Cerebrospinal Fluid of Patients With Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by the presence of neurofibrillary tangles, constituted by tau protein, and plaques formed by amyloid-beta protein. The disease courses with high neural damage, which leads to memory loss and death. Here we analyzed the presence of CX3CL1, a chemokine expressed by neurons, in cerebrospinal fluid (CSF) samples from control subjects and patients with mild cognitive impairment and AD dementia. CX3CL1 was decreased in the CSF of AD dementia patients compared to control subjects. However, there was not difference in plasma samples from the same subjects.

C-Terminal Fragment, Aβ39-42-Based Tetrapeptides Mitigates Amyloid-β Aggregation-Induced Toxicity

Since the introduction of acetyl cholinesterase inhibitors as the first approved drugs by the US Food and Drug Administration for Alzheimer's disease (AD) in clinics, less than satisfactory success in the design of anti-AD agents has impelled the scientists to also focus toward inhibition of Aβ aggregation. Considering the specific binding of fragments for their parent peptide, herein, we synthesized more than 40 new peptides based on a C-terminus tetrapeptide fragment of Aβ_1-42. Initial screening by MTT cell viability assay and supportive results by ThT fluorescence assay led us to identify a tetrapeptide showing complete inhibition for Aβ_1-42 aggregation. Peptide 20 displayed 100% cell viability at 20 μM concentration, while at lower concentrations of 10 and 2 μM 76.6 and 70% of cells were viable. Peptide 20 was found to restrict the conformational transition of Aβ_1-42 peptide toward β-sheet structure. Inhibitory activity of tetrapeptide 20 was further evidenced by the absence of Aβ_1-42 aggregates in electron microscopy. Peptide 20 and other significantly active tetrapeptide analogues could prove imperative in the future design of anti-AD agents.

Nicotine and methyl vinyl ketone, major components of cigarette smoke extracts, increase protective amyloid-β peptides in cells harboring amyloid-β precursor protein

The increased ratio of longer amyloid-β (Aβ1-42)/shorter amyloid-β (Aβ1-40) peptides, generated from amyloid precursor protein (APP), is known to promote the development of Alzheimer's disease (AD). To investigate the role of smoking in Aβ production, we determined the production of Aβ species in the presence of nicotine or methyl vinyl ketone (MVK), major components of cigarette smoke extracts, in Flp-In^™ T-REx^™-293 (T-REx293) cells harboring a single copy of human APP. While treatment with nicotine or MVK did not affect the amount of APP, the levels of Aβ1-40 in the culture media were significantly increased. On the other hand, the levels of Aβ1-42 were unaltered by nicotine or MVK treatment. The Aβ1-42/Aβ1-40 ratio was therefore attenuated by cigarette smoke extracts. Similar results were obtained in T-REx293 cells harboring APP of Swedish- or London-type mutation linked to familial AD. T-REx293 cells expressed the nicotinic acetylcholine receptor (nAchR) and tubocurarine, an nAChR antagonist, completely blocked the effects of nicotine. Treatment with nicotine significantly elevated cellular levels of β-secretase that cleaves APP prior to Aβ generation. Taken together, a protective role of nicotine against AD pathology was suggested by enhanced extracellular Aβ1-40 production, which may suppress Aβ fibrillogenesis.

Simultaneous Determination of Chrysin and Tectochrysin from Alpinia oxyphylla Fruits by UPLC-MS/MS and Its Application to a Comparative Pharmacokinetic Study in Normal and Dementia Rats

A simple and rapid ultra-performance liquid chromatography⁻tandem mass spectrometry (UPLC⁻MS/MS) coupled with a one-step liquid-liquid extraction method has been developed and validated for the simultaneous determination of two flavonoids (chrysin, tectochrysin) from Alpinia oxyphylla fruits extract in rat plasma. Plasma samples were extracted with diethyl ether and separated on an ACQUITY UPLC BEH C₁₈ column (100 mm × 2.1 mm, 1.7 μm) using gradient elution consisting of 0.1% formic acid in water (A) and methanol (B). The multiple reaction monitoring (MRM) mode with electrospray ionization in the positive ion mode was used for detection. The linear range was 0.1 ng/mL to 50 ng/mL for chrysin and tectochrysin, respectively. The accuracy (relative error, RE%) ranged from -8.8% to 7.5% and the intra-day and inter-day precision were within 15% and had a mean extraction recovery rate of 80.3% to 86.7%. The validated method was applied to a comparative pharmacokinetic study after oral administration of Alpinia oxyphylla fruit ethanol extract between normal rats and dementia rats. The area under the curve (AUC) and peak plasma concentration (C_max) of the two constituents were remarkably increased in dementia rats than in normal rats.

N-Terminal Charged Residues of Amyloid-β Peptide Modulate Amyloidogenesis and Interaction with Lipid Membrane

Interactions of amyloid-β (Aβ) peptides and cellular membranes are proposed to be closely related with Aβ neurotoxicity in Alzheimer's disease. In this study, we systematically investigated the effect of the N-terminal hydrophilic region of Aβ40 on its amyloidogenesis and interaction with supported phospholipid bilayer. Our results show that modulation of the charge properties of the dynamic N-terminal region dramatically influences the aggregation properties of Aβ. Furthermore, our results demonstrate that the N-terminal charged residues play a crucial role in driving the early adsorption and latter remobilization of the peptide on membrane bilayer, and mediating the rigidity and viscoelasticity properties of the bound Aβ40 at the membrane interface. The results provide new mechanistic insight into the early Aβ-membrane interactions and binding, which may be critical for elucidating membrane-mediated Aβ amyloidogenesis in a physiological environment and unravelling the origin of Aβ neurotoxicity.

Design of novel amyloid β aggregation inhibitors using QSAR, pharmacophore modeling, molecular docking and ADME prediction

The inhibition of abnormal amyloid β (Aβ) aggregation has been regarded as a good target to control Alzheimer's disease. The present study adopted 2D-QSAR, HQSAR and 3D QSAR (CoMFA & CoMSIA) modeling approaches to identify the structural and physicochemical requirements for the potential Aβ aggregation inhibition. A structure-based molecular docking technique is utilized to approve the features that are obtained from the ligand-based techniques on 30 curcumin derivatives. The combined outputs were then used to screen the modified 10 compounds. The 2D QSAR model on curcumin derivatives gave statistical values R2 = 0.9086 and SEE = 0.1837. The model was further confirmed by Y-randomization test and Applicability domain analysis by the standardization approach. The HQSAR study (Q2 = 0.615, Rncv 2 = 0.931, Rpred 2 = 0.956) illustrated the important molecular fingerprints for inhibition. Contour maps of 3D QSAR models, CoMFA (Q2 = 0.687, Rncv 2 = 0.787, Rpred 2 = 0.731) and CoMSIA (Q2 = 0.743, Rncv 2 = 0.972, Rpred 2 = 0.713), depict that the models are robust and provide explanation of the important features, like steric, electrostatic and hydrogen bond acceptor, which play important role for interaction with the receptor site cavity. The molecular docking study of the curcumin derivatives elucidates the important interactions between the amino acid residues at the catalytic site of the receptor and the ligands, indicating the structural requirements of the inhibitors. The ligand-receptor interactions of top hits were analyzed to explore the pharmacophore features of Aβ aggregation inhibition. The Aβ aggregation inhibitory activities of novel chemical entities were then obtained through inverse QSAR. The newly designed molecules were further screened through machine learning, prediction of toxicity and nature of metabolism to get the proposed six lead compounds.

An exploration of the role of a fish-oriented diet in cognitive decline: a systematic review of the literature

Epidemiological studies have presented inconsistent evidence of the correlation between a fish-oriented dietary intake (FDI) and the risk of cognitive decline. To address these controversies, we performed this systematic review of prospective studies published in December 2016 and earlier using PubMed, Embase, and Web of Science. Two independent researchers conducted the eligibility assessment and data extraction; all discrepancies were solved by discussion with a third researcher. The pooled relative risks (RRs) focused on the incidence of events were estimated with 95% confidence intervals (CIs). Overall, nine studies containing 28,754 subjects were analyzed. When the highest and lowest categories of fish consumption were compared, the summary RR for dementia of Alzheimer type (DAT) was 0.80 (95%CI = 0.65–0.97); i.e., people with a higher intake of fish had a 20% (95%CI = 3–35%) decreased risk of DAT. Additionally, the dose-response synthesized data indicated that a 100-g/week increase in fish intake reduced the risk of DAT by an additional 12% (RR = 0.88, 95%CI = 0.79–0.99). Non-significant results were observed for the risk of dementia of all causes (DAC) and mild cognitive impairment (MCI). Limited evidence involving heterogeneity was found within subgroups or across studies. In conclusion, this review confirmed that a higher intake of fish could be correlated with a reduced risk of DAT. Further research, especially prospective studies that specifically quantify FDI, will help find a more accurate assessment of the different levels of dietary intake.

Sideritis scardica extracts inhibit aggregation and toxicity of amyloid-β in Caenorhabditis elegans used as a model for Alzheimer's disease

Background

Beyond its traditional uses in the Balkan area, Sideritis scardica (known as Greek mountain tea, Lamiaceae) is currently extensively investigated for its pharmacological activity in the central nervous system. Antidepressant, psychostimulating, cognition-enhancing and neuroprotective properties have been described. In this study, we tested hydroalcoholic extracts of S. scardica for their potential to counteract amyloid-β toxicity and aggregation, which plays a crucial role in the pathogenesis of Alzheimer's disease.

Methods

For this purpose, we have chosen the nematode Caenorhabditis elegans, which is used as a model organism for neurodegenerative diseases. The concentration of different polyphenols in extracts prepared from water, 20, 40, 50, and 70% ethanol was analysed by HPLC. Additionally, polar and unpolar fractions were prepared from the 40% ethanolic extract and phytochemically analysed.

Results

Essentially, the contents of all measured constituents increased with the lipophilicity of the extraction solvents. Treatment of transgenic C. elegans strains expressing amyloid-β with the extracts resulted in a reduced number of peptide aggregates in the head region of the worms and alleviated toxicity of amyloid-β, observable through the degree of paralysed animals. The mid-polar extracts (40 and 50% ethanol) turned out be the most active, decreasing the plaque number by 21% and delaying the amyloid-β-induced paralysis by up to 3.5 h. The more lipophilic extract fractions exhibited higher activity than the hydrophilic ones.

Discussion

Sideritis scardica extracts demonstrated pharmacological activity against characteristics of Alzheimer's disease also in C. elegans, supporting current efforts to assess its potential for the treatment of cognitive decline. The active principle as well as the mode of action needs to be investigated in more detail.

Tocotrienol-Rich Fraction Modulates Amyloid Pathology and Improves Cognitive Function in AβPP/PS1 Mice

Alzheimer’s disease (AD) is the most common cause of dementia. The cardinal neuropathological characteristic of AD is the accumulation of amyloid-β (Aβ) into extracellular plaques that ultimately disrupt neuronal function and lead to neurodegeneration. One possible therapeutic strategy therefore is to prevent Aβ aggregation. Previous studies have suggested that vitamin E analogs slow AD progression in humans. In the present study, we investigated the effects of the tocotrienol-rich fraction (TRF), a mixture of vitamin E analogs from palm oil, on amyloid pathology in vitro and in vivo. TRF treatment dose-dependently inhibited the formation of Aβ fibrils and Aβ oligomers in vitro. Moreover, daily TRF supplementation to AβPPswe/PS1dE9 double transgenic mice for 10 months attenuated Aβ immunoreactive depositions and thioflavin-S-positive fibrillar type plaques in the brain, and eventually improved cognitive function in the novel object recognition test compared with control AβPPswe/PS1dE9 mice. The present result indicates that TRF reduced amyloid pathology and improved cognitive functions, and suggests that TRF is a potential therapeutic agent for AD.

Ganglioside-Mediated Assembly of Amyloid β-Protein: Roles in Alzheimer's Disease

Assembly and deposition of amyloid β-protein (Aβ) is an early and invariable pathological event of Alzheimer's disease (AD), a chronic neurodegenerative disease affecting the neurons in the brain of aging population. Thus, clarification of the molecular mechanism underlying Aβ assembly is crucial not only for understanding the pathogenesis of AD, but also for developing disease-modifying remedies. In 1995, ganglioside-bound Aβ (GAβ), with unique molecular characteristics, including its altered immunoreactivity and its conspicuous ability to accelerate Aβ assembly, was discovered in an autopsied brain showing early pathological changes of AD. Based on these findings, it was hypothesized that GAβ is an endogenous seed for amyloid fibril formation in the AD brain. A body of evidence that supports the GAβ hypothesis has been growing for over 20years as follows. First, the conformational changes of Aβ from a random coil to an α-helix, and then to a β-sheet in the presence of ganglioside were validated by several techniques. Second, the seed activity of GAβ to accelerate the assembly of soluble Aβ into amyloid fibrils was confirmed by various in vitro and in vivo experiments. Third, it was found that the Aβ binding to ganglioside to form GAβ occurs under limited conditions, which were provided by the lipid environment surrounding ganglioside. Fourth, the region-specific Aβ deposition in the brain appeared to be dependent on the presence of the lipid environment that was in favor of GAβ generation. In this chapter, further progress of the study of ganglioside-mediated Aβ assembly, especially from the aspects of physicochemistry, structural biology, and neuropathology, is reviewed.

Mutations in the β-amyloid precursor protein in familial Alzheimer's disease increase Aβ oligomer production in cellular models

Soluble oligomers of amyloid-β (Aβ) peptides (AβOs) contribute to neurotoxicity in Alzheimer’s disease (AD). However, it currently remains unknown whether an increase in AβOs is the common phenotype in cellular and animal models. Furthermore, it has not yet been established whether experimental studies conducted using models overexpressing mutant genes of the amyloid precursor protein (APP) are suitable for investigating the underlying molecular mechanism of AD. We herein employed the Flp-In™ T-REx™-293 (T-REx 293) cellular system transfected with a single copy of wild-type, Swedish-, Dutch-, or London-type APP, and quantified the levels of Aβ monomers (Aβ1-40 and Aβ1-42) and AβOs using an enzyme-linked immunosorbent assay (ELISA). The levels of extracellular AβOs were significantly higher in Dutch- and London-type APP-transfected cells than in wild-type APP-transfected cells. Increased levels were also observed in Swedish-type APP-transfected cells. On the other hand, intracellular levels of AβOs were unaltered among wild-type and mutant APP-transfected cells. Intracellular levels of Aβ monomers were undetectable, and no common abnormality was observed in their extracellular levels or ratios (Aβ1-42/Aβ1-40) among the cells examined. We herein demonstrated that increased levels of extracellular AβOs are the common phenotype in cellular models harboring different types of APP mutations. Our results suggest that extracellular AβOs play a key role in the pathogenesis of AD.

Insulin degrading enzyme contributes to the pathology in a mixed model of Type 2 diabetes and Alzheimer's disease: possible mechanisms of IDE in T2D and AD

Insulin degrading enzyme (IDE) is believed to act as a junction point of Type 2 diabetes (T2D) and Alzheimer's disease (AD); however, the underlying mechanism was not completely clear yet. Transgenic APPSwe/PS1 mice were used as the AD model and were treated with streptozocin/streptozotocin (STZ) to develop a mixed mice model presenting both AD and T2D. Morris Water Maze (MWM) and recognition task were performed to trace the cognitive function. The detection of fasting plasma glucose (FPG) and plasma insulin concentration, and oral glucose tolerance test (OGTT) were used to trace the metabolism evolution. Aβ40 and Aβ42 were quantified by colorimetric ELISA kits. The mRNA or protein expression levels were determined by quantitative real-time RT-PCR and Western blotting analysis respectively. T2D contributes to the AD progress by accelerating and worsening spatial learning and recognition impairments. Metabolic parameters and glucose tolerance were significantly changed in the presence of the AD and T2D. The expression levels of IDE, PPARγ, and AMPK were down-regulated in mice with AD and T2D. PPARγ activator rosiglitazone (RSZ) or AMPK activator AICAR increased the expression level of IDE and decreased Aβ levels in mice with AD and T2D. RSZ or AICAR treatment also alleviated the spatial learning and recognition impairments in AD and T2D mice. Our results found that, in the mice with T2D and AD, the activators of PPARγ/AMPK signaling pathway significantly increased the expression level of IDE, and decreased the accumulation of Aβ40 and Aβ42, as well as alleviated the spatial learning and recognition impairments.

Use of cholinesterase inhibitors in dementia

Alzheimer's disease is the most common cause of dementia in older people, with about half a million people affected in the UK. Its effects are devastating and far-reaching for sufferers, their carers and society in general – the Audit Commission estimated the annual cost of dementia care for 1998–1999 at £6.1 billion (Audit Commission, 2000). There is no cure and it is terminal within 3 to 7 years of diagnosis. Given an estimated doubling of dementia cases over the next 50 years (Melzer et al, 1997), the burden of care is set to increase substantially.

Extracellular Matrix Remodeling in Human Disease

The extracellular matrix (ECM) is a meshwork of proteins and carbohydrates that supports many biological structures and processes, from tissue development and elasticity to preserve the structures of entire organs. In each organ, the composition of the ECM is distinct. It is a remarkably active three-dimensional structure that is continuously undergoing remodeling to regulate tissue homeostasis. This review aims to explain the role of ECM proteins in the remodeling process in different types of disease. The hardening of the ECM (desmoplasia), as well as its manipulation, induction, and impairment in regulation of its composition can play a role in several diseases, examples of which are chronic obstructive pulmonary disease, pancreatic ductal adenocarcinoma, spinal cord injury, progression and metastasis of breast cancer, and neurodegenerative condition in the brain such as Alzheimer's disease. Remodeling is also associated with diet-induced insulin resistance in many metabolic tissues. A greater comprehension of the way in which the ECM regulates organ structure and function and of how ECM remodeling affects the development of diseases may lead to the improvement and discovery of new treatments.

Assemblies of amyloid-β30-36 hexamer and its G33V/L34T mutants by replica-exchange molecular dynamics simulation

The aggregation of amyloid-β peptides is associated with the pathogenesis of Alzheimer’s disease, in which the 30–36 fragments play an important part as a fiber-forming hydrophobic region. The fibrillar structure of Aβ_30–36 has been detected by means of X-ray diffraction, but its oligomeric structural determination, biophysical characterization, and pathological mechanism remain elusive. In this study, we have investigated the structures of Aβ_30–36 hexamer as well as its G33V and L34T mutants in explicit water environment using replica-exchange molecular dynamics (REMD) simulations. Our results show that the wild-type (WT) Aβ_30–36 hexamer has a preference to form β-barrel and bilayer β-sheet conformations, while the G33V or L34T mutation disrupts the β-barrel structures: the G33V mutant is homogenized to adopt β-sheet-rich bilayers, and the structures of L34T mutant on the contrary get more diverse. The hydrophobic interaction plays a critical role in the formation and stability of oligomeric assemblies among all the three systems. In addition, the substitution of G33 by V reduces the β-sheet content in the most populated conformations of Aβ_30–36 oligomers through a steric effect. The L34T mutation disturbs the interpeptide hydrogen bonding network, and results in the increased coil content and morphological diversity. Our REMD runs provide structural details of WT and G33V/L34T mutant Aβ_30–36 oligomers, and molecular insight into the aggregation mechanism, which will be helpful for designing novel inhibitors or amyloid-based materials.

Dual Role of Gold Nanorods: Inhibition and Dissolution of Aβ Fibrils Induced by Near IR Laser

Extracellular plaques of amyloid beta (Aβ) fibrils and neurofibrillary tangles are known to be associated with neurological diseases such as Alzheimer's disease. Studies have shown that spherical nanoparticles inhibit the formation of Aβ fibrils by intercepting the nucleation and growth pathways of fibrillation. In this report, gold nanorods (AuNRs) are used to inhibit the formation of Aβ fibrils and the shape-dependent plasmonic properties of AuNRs are exploited to faciliate faster dissolution of mature Aβ fibrils. Negatively charged, lipid (DMPC) stabilized AuNRs inhibit the formation of fibrils due to selective binding to the positevly charged amyloidogenic sequence of Aβ protein. The kinetics of inhibition is characterized by thioflavin T (ThT) fluorescence, transmission electronic microscopy (TEM), atomic force microscopy (AFM), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). An increase in the aspect ratio of DMPC-AuNR in the range of 2.2-4.2 decreased the fibrils content proportionally. Further, the fibrils content is decreased by increasing the concentration of AuNR for all aspect ratios. As AuNR absorb near-infrared (NIR) light and creates a localized hotspot, NIR laser (800 nm) is applied for 2 min to facilitate the thermal dissolution of mature Aβ fibrils. Majority of Aβ fibrils are disintegrated into smaller fragments after exposure to NIR in the presence of AuNR. Thus, the DMPC-AuNRs exhibit a dual effect: inhibition of fibrillation and NIR laser facilitated dissolution of mature amyloid fibrils. This study essentially provides guidelines to design efficient nanoparticle-based therapeutics for neurodegenerative diseases.

Single-Base Resolution Mapping of 5-Hydroxymethylcytosine Modifications in Hippocampus of Alzheimer's Disease Subjects

Epigenetic modifications to cytosine have been shown to regulate transcription in cancer, embryonic development, and recently neurodegeneration. While cytosine methylation studies are now common in neurodegenerative research, hydroxymethylation studies are rare, particularly genome-wide mapping studies. As an initial study to analyze 5-hydroxymethylcytosine (5-hmC) in the Alzheimer's disease (AD) genome, reduced representation hydroxymethylation profiling (RRHP) was used to analyze more than 2 million sites of possible modification in hippocampal DNA of sporadic AD and normal control subjects. Genes with differentially hydroxymethylated regions were filtered based on previously published microarray data for altered gene expression in hippocampal DNA of AD subjects. Our data show significant pathways for altered levels of 5-hmC in the hippocampus of AD subjects compared to age-matched normal controls involved in signaling, energy metabolism, cell function, gene expression, protein degradation, and cell structure and stabilization. Overall, our data suggest a possible role for the dysregulation of epigenetic modifications to cytosine in late stage AD.

Premature or pathological aging: longevity

Abstract The main objective of this literature review was to summarize and characterize the main factors and events that may negatively influence quality of life and human longevity. The factors that act on premature aging processes are essentially the same as those of natural or healthy aging, but in a more intense and uncontrolled manner. Such factors are: 1) genetic (genome); 2) metabolic (metabolome); 3) environmental (life conditions and style, including diet). Factors 1 and 2 are more difficult to control by individuals; once depending on socioeconomic, cultural and educational conditions. Differently of environmental factors that may be totally controlled by individuals. Unfamiliarity with these factors leads to chronic and/or degenerative diseases that compromise quality of life and longevity.

Emergence of Alternative Structures in Amyloid Beta 1-42 Monomeric Landscape by N-terminal Hexapeptide Amyloid Inhibitors

Alzheimer’s disease (AD) is characterized by deposition of amyloid beta (Aβ) peptides into senile plaques in the brain. While most familial mutations are associated with early-onset AD, recent studies report the AD-protective nature of two genetic human Aβ variants, i.e. A2T and A2V, in the heterozygous state. The mixture of A2V Aβ1-6 (Aβ₆) hexapeptide and WT Aβ1–42 (Αβ₄₂) is also found neuroprotective. Motivated by these findings, in this study we investigate the effects of WT, A2V, and A2T Aβ₆ hexapeptide binding on the monomeric WT Aβ₄₂ landscape. For this purpose, we have performed extensive atomistic Replica Exchange Molecular Dynamics simulations, elucidating preferential binding of Aβ₄₂ with the A2V and A2T hexapeptides compared to WT Aβ₆. A notable reorganization of the Aβ₄₂ landscape is revealed due to hexapeptide association, as manifested by lowering of transient interactions between the central and C-terminal hydrophobic patches. Concurrently, Aβ₆-bound Aβ₄₂ monomer exhibits alternative structural features that are strongly dependent on the hexapeptide sequence. For example, a central helix is more frequently populated within the A2T-bound monomer, while A2V-bound Aβ₄₂ is often enhanced in overall disorder. Taken together, the present simulations offer novel molecular insights onto the effect of the N-terminal hexapeptide binding on the Aβ₄₂ monomer structure, which might help in explaining their reported amyloid inhibition properties.

Attenuation of β-Amyloid Toxicity In Vitro and In Vivo by Accelerated Aggregation

Accumulation and aggregation of β-amyloid (Aβ) peptides result in neuronal death, leading to cognitive dysfunction in Alzheimer's disease. The self-assembled Aβ molecules form various intermediate aggregates including oligomers that are more toxic to neurons than the mature aggregates, including fibrils. Thus, one strategy to alleviate Aβ toxicity is to facilitate the conversion of Aβ intermediates to larger aggregates such as fibrils. In this study, we designed a peptide named A3 that significantly enhanced the formation of amorphous aggregates of Aβ by accelerating the aggregation kinetics. Thioflavin T fluorescence experiments revealed an accelerated aggregation of Aβ monomers, accompanying reduced Aβ cytotoxicity. Transgenic Caenorhabditis elegans over-expressing amyloid precursor protein exhibited paralysis due to the accumulation of Aβ oligomers, and this phenotype was attenuated by feeding the animals with A3 peptide. These findings suggest that the Aβ aggregation-promotion effect can potentially be useful for developing strategies to reduce Aβ toxicity.

Chemical Methods to Knock Down the Amyloid Proteins

Amyloid proteins are closely related with amyloid diseases and do tremendous harm to human health. However, there is still a lack of effective strategies to treat these amyloid diseases, so it is important to develop novel methods. Accelerating the clearance of amyloid proteins is a favorable method for amyloid disease treatment. Recently, chemical methods for protein reduction have been developed and have attracted much attention. In this review, we focus on the latest progress of chemical methods that knock down amyloid proteins, including the proteolysis-targeting chimera (PROTAC) strategy, the "recognition-cleavage" strategy, the chaperone-mediated autophagy (CMA) strategy, the selectively light-activatable organic and inorganic molecules strategy and other chemical strategies.

Microphysiological Human Brain and Neural Systems-on-a-Chip: Potential Alternatives to Small Animal Models and Emerging Platforms for Drug Discovery and Personalized Medicine

Translational challenges associated with reductionist modeling approaches, as well as ethical concerns and economic implications of small animal testing, drive the need for developing microphysiological neural systems for modeling human neurological diseases, disorders, and injuries. Here, we provide a comprehensive review of microphysiological brain and neural systems-on-a-chip (NSCs) for modeling higher order trajectories in the human nervous system. Societal, economic, and national security impacts of neurological diseases, disorders, and injuries are highlighted to identify critical NSC application spaces. Hierarchical design and manufacturing of NSCs are discussed with distinction for surface- and bulk-based systems. Three broad NSC classes are identified and reviewed: microfluidic NSCs, compartmentalized NSCs, and hydrogel NSCs. Emerging areas and future directions are highlighted, including the application of 3D printing to design and manufacturing of next-generation NSCs, the use of stem cells for constructing patient-specific NSCs, and the application of human NSCs to 'personalized neurology'. Technical hurdles and remaining challenges are discussed. This review identifies the state-of-the-art design methodologies, manufacturing approaches, and performance capabilities of NSCs. This work suggests NSCs appear poised to revolutionize the modeling of human neurological diseases, disorders, and injuries.

DNA-PK and P38 MAPK: A Kinase Collusion in Alzheimer's Disease?

The pathogenesis of Alzheimer's disease (AD), characterized by prevalent neuronal death and extracellular deposit of amyloid plaques, is poorly understood. DNA lesions downstream of reduced DNA repair ability have been reported in AD brains. Neurons predominantly use a mechanism to repair double-strand DNA breaks (DSB), which is non-homologous end joining (NHEJ). NHEJ requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK is a holoenzyme comprising the p460 kD catalytic subunit (DNA-PKcs) and its activator Ku, a heterodimer of p86 and p70 subunits. Ku first binds and then recruits DNA-PKcs to double-stranded DNA ends before NHEJ process begins. Studies have shown reduced NHEJ activity as well as DNA-PKcs and Ku protein levels in AD brains suggesting possible contribution of unrepaired DSB to AD development. However, normal aging brains also show reduced DNA-PKcs and Ku levels thus challenging the notion of any direct link between NHEJ and AD. Another kinase, p38 MAPK is induced by various DNA damaging agents and DSB itself. Increased DNA damage with aging could induce p38 MAPK and its induction may be sustained when DNA repair is compromised in the brain with reduced DNA-PK activity. Combined, these two events may potentially set the stage for an awry nervous system approaching AD.

Polysaccharides from Ganoderma lucidum attenuate microglia-mediated neuroinflammation and modulate microglial phagocytosis and behavioural response

Background

Ganoderma lucidum (GL) has been widely used in Asian countries for hundreds of years to promote health and longevity. The pharmacological functions of which had been classified, including the activation of innate immune responses, suppression of tumour and modulation of cell proliferations. Effective fractions of Ganoderma lucidum polysaccharides (GLP) had already been reported to regulate the immune system. Nevertheless, the role of GLP in the microglia-mediated neuroinflammation has not been sufficiently elucidated. Further, GLP effect on microglial behavioural modulations in correlation with the inflammatory responses remains to be unravelled. The aim of this work was to quantitatively analyse the contributions of GLP on microglia.

Methods

The BV2 microglia and primary mouse microglia were stimulated by lipopolysaccharides (LPS) and amyloid beta₄₂ (Aβ₄₂) oligomer, respectively. Investigation on the effect of GLP was carried by quantitative determination of the microglial pro- and anti-inflammatory cytokine expressions and behavioural modulations including migration, morphology and phagocytosis. Analysis of microglial morphology and phagocytosis modulations was confirmed in the zebrafish brain.

Results

Quantitative results revealed that GLP down-regulates LPS- or Aβ-induced pro-inflammatory cytokines and promotes anti-inflammatory cytokine expressions in BV-2 and primary microglia. In addition, GLP attenuates inflammation-related microglial migration, morphological alterations and phagocytosis probabilities. We also showed that modulations of microglial behavioural responses were associated with MCP-1 and C1q expressions.

Conclusions

Overall, our study provides an insight into the GLP regulation of LPS- and Aβ-induced neuroinflammation and serves an implication that the neuroprotective function of GLP might be achieved through modulation of microglial inflammatory and behavioural responses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0839-0) contains supplementary material, which is available to authorized users.

Rationally Designed Peptides and Peptidomimetics as Inhibitors of Amyloid-β (Aβ) Aggregation: Potential Therapeutics of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease with no clinically accepted treatment to cure or halt its progression. The worldwide effort to develop peptide-based inhibitors of amyloid-β (Aβ) aggregation can be considered an unplanned combinatorial experiment. An understanding of what has been done and achieved may advance our understanding of AD pathology and the discovery of effective therapeutic agents. We review here the history of such peptide-based inhibitors, including those based on the Aβ sequence and those not derived from that sequence, containing both natural and unnatural amino acid building blocks. Peptide-based aggregation inhibitors hold significant promise for future AD therapy owing to their high selectivity, effectiveness, low toxicity, good tolerance, low accumulation in tissues, high chemical and biological diversity, possibility of rational design, and highly developed methods for analyzing their mode of action, proteolytic stability (modified peptides), and blood-brain barrier (BBB) permeability.

Multiregional analysis of global 5-methylcytosine and 5-hydroxymethylcytosine throughout the progression of Alzheimer's disease

Epigenetic modifications to cytosine are known to alter transcriptional states and deregulate gene expression in cancer, embryonic development, and most recently in neurodegeneration. To test the hypothesis that global levels of cytosine modification are altered throughout the progression of Alzheimer's disease, 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) were quantified using gas chromatography/mass spectrometry (GC/MS) and stable labeled internal standards of cytosine, 5-mC, and 5-hmC. Cytosine modifications were quantified in DNA extracted from tissue specimens of four brain regions (cerebellum, inferior parietal lobe, superior and middle temporal gyrus, and hippocampus/parahippocampal gyrus) of cognitively normal control (NC) subjects and subjects with mild cognitive impairment (MCI), preclinical Alzheimer's disease (PCAD), late onset Alzheimer's disease, frontotemporal lobar degeneration (FTLD) and dementia with Lewy bodies (DLB). Repeated measures analyses of the data show significant alterations in 5-mC and 5-hmC in early stages of Alzheimer's disease (PCAD and MCI), as well as FTLD and DLB subjects, across multiple regions of the brain. These data suggest alterations in epigenetic regulation of genes may play an early role in the progression of AD as well as other types of neurodegeneration.

Extracellular matrix proteomics in schizophrenia and Alzheimer's disease

Brain extracellular matrix (ECM) is a highly organized system that consists of collagens, noncollagenous proteins, glycoproteins, hyaluronan, and proteoglycans. Recognized physiological roles of ECM include developmental regulation, tissue homeostasis, cell migration, cell proliferation, cell differentiation, neuronal plasticity, and neurite outgrowth. Aberrant ECM structure is associated with brain neurodegenerative conditions. This review focuses on two neurodegenerative conditions, schizophrenia and Alzheimer's disease, and summarizes recent findings of altered ECM components, including proteoglycans, glycosaminoglycans, proteins, and glycoproteins, and proteins and genes related to other brain components. The scope includes immunohistochemical, genomics, transcriptomics, proteomics, and glycomics studies, and a critical assessment of current state of proteomic studies for neurodegenerative disorders. The intent is to summarize the ECM molecular alterations associated with neurodegenerative pathophysiology. Graphical Abstract Brain extracellular matrix showing HSPGs, CSPGs, HA, collagens, and other glycoproteins.

Genome instability in Alzheimer disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Autosomal dominant, familial AD (fAD) is very rare and caused by mutations in amyloid precursor protein (APP), presenilin-1 (PSEN-1), and presenilin-2 (PSEN-2) genes. The pathogenesis of sporadic AD (sAD) is more complex and variants of several genes are associated with an increased lifetime risk of AD. Nuclear and mitochondrial DNA integrity is pivotal during neuronal development, maintenance and function. DNA damage and alterations in cellular DNA repair capacity have been implicated in the aging process and in age-associated neurodegenerative diseases, including AD. These findings are supported by research using animal models of AD and in DNA repair deficient animal models. In recent years, novel mechanisms linking DNA damage to neuronal dysfunction have been identified and have led to the development of noninvasive treatment strategies. Further investigations into the molecular mechanisms connecting DNA damage to AD pathology may help to develop novel treatment strategies for this debilitating disease. Here we provide an overview of the role of genome instability and DNA repair deficiency in AD pathology and discuss research strategies that include genome instability as a component.

Clinical implications from proteomic studies in neurodegenerative diseases: lessons from mitochondrial proteins

Mitochondria play a key role in eukaryotic cells, being mediators of energy, biosynthetic and regulatory requirements of these cells. Emerging proteomics techniques have allowed scientists to obtain the differentially expressed proteome or the proteomic redox status in mitochondria. This has unmasked the diversity of proteins with respect to subcellular location, expression and interactions. Mitochondria have become a research 'hot spot' in subcellular proteomics, leading to identification of candidate clinical targets in neurodegenerative diseases in which mitochondria are known to play pathological roles. The extensive efforts to rapidly obtain differentially expressed proteomes and unravel the redox proteomic status in mitochondria have yielded clinical insights into the neuropathological mechanisms of disease, identification of disease early stage and evaluation of disease progression. Although current technical limitations hamper full exploitation of the mitochondrial proteome in neurosciences, future advances are predicted to provide identification of specific therapeutic targets for neurodegenerative disorders.

Increased Amyloid Precursor Protein and Tau Expression Manifests as Key Secondary Cell Death in Chronic Traumatic Brain Injury

In testing the hypothesis of Alzheimer's disease (AD)‐like pathology in late stage traumatic brain injury (TBI), we evaluated AD pathological markers in late stage TBI model. Sprague–Dawley male rats were subjected to moderate controlled cortical impact (CCI) injury, and 6 months later euthanized and brain tissues harvested. Results from H&E staining revealed significant 33% and 10% reduction in the ipsilateral and contralateral hippocampal CA3 interneurons, increased MHCII‐activated inflammatory cells in many gray matter (8–20‐fold increase) and white matter (6–30‐fold increased) regions of both the ipsilateral and contralateral hemispheres, decreased cell cycle regulating protein marker by 1.6‐ and 1‐fold in the SVZ and a 2.3‐ and 1.5‐fold reductions in the ipsilateral and contralateral dentate gyrus, diminution of immature neuronal marker by two‐ and onefold in both the ipsilateral and contralateral SVZ and dentate gyrus, and amplified amyloid precursor protein (APP) distribution volumes in white matter including corpus callosum, fornix, and internal capsule (4–38‐fold increase), as well as in the cortical gray matter, such as the striatum hilus, SVZ, and dentate gyrus (6–40‐fold increase) in TBI animals compared to controls (P's < 0.001). Surrogate AD‐like phenotypic markers revealed a significant accumulation of phosphorylated tau (AT8) and oligomeric tau (T22) within the neuronal cell bodies in ipsilateral and contralateral cortex, and dentate gyrus relative to sham control, further supporting the rampant neurodegenerative pathology in TBI secondary cell death. These findings indicate that AD‐like pathological features may prove to be valuable markers and therapeutic targets for late stage TBI. J. Cell. Physiol. 232: 665–677, 2017. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Modulating the Effects of the Bacterial Chaperonin GroEL on Fibrillogenic Polypeptides through Modification of Domain Hinge Architecture

The isolated apical domain of the Escherichia coli GroEL subunit displays the ability to suppress the irreversible fibrillation of numerous amyloid-forming polypeptides. In previous experiments, we have shown that mutating Gly-192 (located at hinge II that connects the apical domain and the intermediate domain) to a tryptophan results in an inactive chaperonin whose apical domain is disoriented. In this study, we have utilized this disruptive effect of Gly-192 mutation to our advantage, by substituting this residue with amino acid residues of varying van der Waals volumes with the intent to modulate the affinity of GroEL toward fibrillogenic peptides. The affinities of GroEL toward fibrillogenic polypeptides such as Aβ(1-40) (amyloid-β(1-40)) peptide and α-synuclein increased in accordance to the larger van der Waals volume of the substituent amino acid side chain in the G192X mutants. When we compared the effects of wild-type GroEL and selected GroEL G192X mutants on α-synuclein fibril formation, we found that the effects of the chaperonin on α-synuclein fibrillation were different; the wild-type chaperonin caused changes in both the initial lag phase and the rate of fibril extension, whereas the effects of the G192X mutants were more specific toward the nucleus-forming lag phase. The chaperonins also displayed differential effects on α-synuclein fibril morphology, suggesting that through mutation of Gly-192, we may induce changes to the intermolecular affinities between GroEL and α-synuclein, leading to more efficient fibril suppression, and in specific cases, modulation of fibril morphology.

Suppression of amyloid fibrils using the GroEL apical domain

In E. coli cells, rescue of non-native proteins and promotion of native state structure is assisted by the chaperonin GroEL. An important key to this activity lies in the structure of the apical domain of GroEL (GroEL-AD) (residue 191–376), which recognizes and binds non-native protein molecules through hydrophobic interactions. In this study, we investigated the effects of GroEL-AD on the aggregation of various client proteins (α-Synuclein, Aβ42, and GroES) that lead to the formation of distinct protein fibrils in vitro. We found that GroEL-AD effectively inhibited the fibril formation of these three proteins when added at concentrations above a critical threshold; the specific ratio differed for each client protein, reflecting the relative affinities. The effect of GroEL-AD in all three cases was to decrease the concentration of aggregate-forming unfolded client protein or its early intermediates in solution, thereby preventing aggregation and fibrillation. Binding affinity assays revealed some differences in the binding mechanisms of GroEL-AD toward each client. Our findings suggest a possible applicability of this minimal functioning derivative of the chaperonins (the “minichaperones”) as protein fibrillation modulators and detectors.

GM1 Ganglioside and the Seeding of Amyloid in Alzheimer’s Disease: Endogenous Seed for Alzheimer Amyloid

A fundamental question about the pathogenesis of Alzheimer’s disease (AD) is how monomeric, nontoxic amyloid β-protein (Aβ) is converted to its toxic aggregates in the brain. The author previously identified a unique Aβ species in the AD brain, which is characterized by its binding to GM1 ganglioside (GM1). On the basis of the molecular characteristics of GM1-bound Aβ (GAβ), the author hypothesized that GM1 plays a critical role in the process. The author recently examined this possibility using a novel monoclonal antibody raised against purified GAβ and validated that GAβ is endogenously generated in the brain and accelerates Aβ assembly by acting as a seed. Furthermore, the author provided a possibility that aging and the expression of apolipoprotein E4 facilitate Aβ assembly in the brain through an increase in the GM1 content in the neuronal membranes, which likely induces GAβ generation. The author’s results imply a mechanism underlying the onset of AD and also provide a new insight into development of novel therapeutic strategy.

C-Terminal Fragment, Aβ32-37, Analogues Protect Against Aβ Aggregation-Induced Toxicity

Amyloid-β aggregation is a major etiological phenomenon in Alzheimer's disease. Herein, we report peptide-based inhibitors that diminish the amyloid load by obviating Aβ aggregation. Taking the hexapeptide fragment, Aβ32-37, as lead, more than 40 new peptides were synthesized. Upon evaluation of the newly synthesized hexapeptides as inhibitors of Aβ toxicity by the MTT-based cell viability assay, a number of peptides exhibited significant Aβ aggregation inhibitory activity at sub-micromolar concentration range. A hexapeptide (1) showed complete mitigation of Aβ toxicity in the cell culture assay at 2 μM. In the ThT fluorescence assay, upon incubation of Aβ with this peptide, we observed no increase in the ThT fluorescence relative to control. The secondary structure estimation by circular dichroism spectroscopy and morphological examination by transmission electron microscopy further confirmed the results.

Part 2. Notch-sparing γ-secretase inhibitors: The study of novel γ-amino naphthyl alcohols

One therapeutic approach for Alzheimer's disease is to inhibit the cleavage of the amyloid precursor protein (APP) by γ-secretase. At the beginning of a series of studies from our laboratories, a series of novel γ-amino alcohols (1) were found to possess γ-secretase inhibitory activity and Notch-sparing effects. A new one-pot synthesis of γ-amino alcohols and the structure-activity relationship (SAR) of these analogs will be discussed.

Part 3: Notch-sparing γ-secretase inhibitors: SAR studies of 2-substituted aminopyridopyrimidinones

In search for novel lead compounds as γ-secretase inhibitors, analogs of aminopyrido[2,3-d]pyrimidin-7-ones (I) were synthesized and evaluated for inhibitory effects on amyloid-β-peptide production and cleavage of the Notch1 receptor mediated by γ-secretase. Selected pyridopyrimidines, such as 1, 8, 9, 10, 11 and 16 are γ-secretase inhibitors that did not have an effect on Notch1 receptor processing.

Impact of Plant-Derived Flavonoids on Neurodegenerative Diseases

Neurodegenerative disorders have a common characteristic that is the involvement of different cell types, typically the reactivity of astrocytes and microglia, characterizing gliosis, which in turn contributes to the neuronal dysfunction and or death. Flavonoids are secondary metabolites of plant origin widely investigated at present and represent one of the most important and diversified among natural products phenolic groups. Several biological activities are attributed to this class of polyphenols, such as antitumor activity, antioxidant, antiviral, and anti-inflammatory, among others, which give significant pharmacological importance. Our group have observed that flavonoids derived from Brazilian plants Dimorphandra mollis Bent., Croton betulaster Müll. Arg., e Poincianella pyramidalis Tul., botanical synonymous Caesalpinia pyramidalis Tul. also elicit a broad spectrum of responses in astrocytes and neurons in culture as activation of astrocytes and microglia, astrocyte associated protection of neuronal progenitor cells, neuronal differentiation and neuritogenesis. It was observed the flavonoids also induced neuronal differentiation of mouse embryonic stem cells and human pluripotent stem cells. Moreover, with the objective of seeking preclinical pharmacological evidence of these molecules, in order to assess its future use in the treatment of neurodegenerative disorders, we have evaluated the effects of flavonoids in preclinical in vitro models of neuroinflammation associated with Parkinson's disease and glutamate toxicity associated with ischemia. In particular, our efforts have been directed to identify mechanisms involved in the changes in viability, morphology, and glial cell function induced by flavonoids in cultures of glial cells and neuronal cells alone or in interactions and clarify the relation with their neuroprotective and morphogetic effects.

Interaction mechanism exploration of HEA derivatives as BACE1 inhibitors by in silico analysis

The β-site amyloid precursor protein cleaving enzyme 1 (BACE1) initiates the generation of β-amyloid (Aβ) peptides which play a critical early role in the pathogenesis of Alzheimer's disease (AD), and thus it is a prime target for lowering the Aβ levels to treat AD.

Effects of Charged Cholesterol Derivatives on Aβ40 Amyloid Formation

Understanding of the mechanistic progess of amyloid-β peptide (Aβ) aggregation is critical for elucidating the underlying pathogenesis of Alzheimer's disease (AD). Herein, we report for the first time the effects of two cholesterol derivatives, negatively charged cholesterol sulfate (cholesterol-SO4) and positively charged 3β-[N-(dimethylaminoethane)carbamoyl]-cholesterol (DC-cholesterol), on the fibrillization of Aβ40. Our results demonstrate that both of the nonvesicular forms of cholesterol-SO4 and DC-cholesterol moderately accelerate the aggregation rate of Aβ40. This effect is similar to that observed for unmodified cholesterol, indicating the importance of hydrophobic interactions in binding of Aβ40 to these steroid molecules. Furthermore, we show that the vesicles formed at higher concentrations of anionic cholesterol-SO4 facilitate Aβ40 aggregation rate markedly. In contrast, the cationic DC-cholesterol vesicles show the ability to inhibit Aβ40 fibril formation under appropriate experimental conditions. The results suggest that the electrostatic interactions between Aβ40 and the charged vesicles can be of great importance in regulating Aβ40-vesicle interaction. Our results also indicate that the structural properties of the aggregates of the cholesterol derivatives, including the surface charge and the size of the vesicles, are critical in regulating the effects of these vesicles on Aβ40 aggregation kinetics.