Inhibitory effect of curcumin on the Al(III)-induced Aβ₄₂ aggregation and neurotoxicity in vitro

The pathogenesis of Alzheimer's disease (AD) involves a key event which changes the morphology of amyloid-β 42 (Aβ)?? peptide from its soluble monomeric form into the fibrillated aggregates in the brain. Aluminum ion, Al(III), is known to act as a pathological chaperone of the Aβ?? in this process; curcumin, a natural phenolic compound, is considered capable of binding Al(III) and Aβ??; nevertheless, little is known about the combined action of curcumin and Al(III) on the Aβ?? fibrillation and neurotoxicity. Here, combinations of circular dichroism spectroscopy, thioflavin T fluorescence, atomic force microscopy, Bradford and MTT assays, it is demonstrated that although Al(III) can promote the Aβ?? fibrillation dose-dependently, leading to the high neurotoxicity to PC12 cells, curcumin can inhibit the events. Besides, we found that curcumin is able not only to inhibit the formation of Al(III)-induced Aβ?? fibrillation, but also to form the Al(III)-curcumin complexes which in turn can remold the preformed, mature, ordered Aβ?? fibrils into the low toxic amorphous aggregates. These findings suggest that curcumin could block the binding of Al(III) with Aβ?? and form the Al(III)-curcumin complexes, so as to inhibit the Al(III)-induced Aβ?? fibrillation and neurotoxicity. The Al(III)-curcumin complexes are worth potentially developing as a therapy agent against the neurodegenerative disorders in the future.     

L17A/F19A Substitutions Augment the α-Helicity of β-Amyloid Peptide Discordant Segment

β-amyloid peptide (Aβ) aggregation has been thought to be associated with the pathogenesis of Alzheimer’s disease. Recently, we showed that L17A/F19A substitutions may increase the structural stability of wild-type and Arctic-type Aβ₄₀ and decrease the rates of structural conversion and fibril formation. However, the underlying mechanism for the increase of structural stability as a result of the alanine substitutions remained elusive. In this study, we apply nuclear magnetic resonance and circular dichroism spectroscopies to characterize the Aβ₄₀ structure, demonstrating that L17A/F19A substitutions can augment the α-helicity of the residues located in the α/β-discordant segment (resides 15 to 23) of both wild-type and Arctic-type Aβ₄₀. These results provide a structural basis to link the α-helicity of the α/β-discordant segment with the conformational conversion propensity of Aβ.     

Peptide Aβ(16-25) forms nanofilms in the process of its aggregation

A method for the synthesis and high purification of fragments of Aβ(1-42) peptide has been elaborated. We have synthesized the amyloidogenic fragment Aβ(16-25) predicted by us and studied the process of its aggregation by electron microscopy and X-ray analysis. Electron microscopy images show that the peptide forms a film, which is not characteristic of amyloid fibrils. At the same time, according to the X-ray diffraction data, its preparations display the presence of two main reflections (4.6-4.8 and 8-12 Å) characteristic of cross-β structure of amyloid fibrils. Thus, the fragment Aβ(16-25) that we predicted is a promising object not only for studying the process of polymerization of the peptides/proteins, but also for using it as a nanomaterial to study a number of biological processes.     

In silico investigation on the inhibition of Aβ42 aggregation by Aβ40 peptide by potential of mean force study

Recent experimental data revealed that small, soluble Amyloid beta (Aβ₄₂) oligomers, especially dimers impair synaptic plasticity and memory leading to Alzheimer’s disease. Here, we have studied dimerization of Aβ₄₂/Aβ₄₂ homo-dimer and Aβ₄₀/Aβ₄₂ hetero-dimer in terms of free energy profile by all-atom simulations using the ff99SB force field. We have found that in the presence of Aβ₄₀ peptide, there exists a strong tendency to form a hetero-dimer with Aβ₄₂ peptide, suggesting that a possible co-oligomerization. Furthermore, we have investigated the effects of Aβ₄₀ on the Aβ₄₂ peptide. Our study also shows that in presence of Aβ₄₀, the beta-content of Aβ₄₂ monomer is reduced. Additionally, certain residues important for bending in Aβ₄₂ peptide attained an increased flexibility in the presence of Aβ₄₀. The salt-bridge destabilization also manifested the impact of Aβ₄₀ on Aβ₄₂ peptide as a whole. Based on this, one may expect that Aβ₄₀ inhibits the aggregation propensity of Aβ₄₂. Moreover, the binding free energy obtained by the molecular mechanics–Poisson–Boltzmann surface area method also revealed a strong affinity between the two isoforms thereby suggests that Aβ₄₀ binding induces conformational change in Aβ₄₂. Our results suggest that co-oligomerization of Aβ isoforms may play a substantial role in Alzheimer’s disease.     

Variable Deposition of Amyloid β-Protein (Aβ) with the Carboxy-Terminus that Ends at Residue Valine40 (Aβ40) in the Cerebral Cortex of Patients with Alzheimer's Disease: A Double-Labeling Immunohistochemical Study with Antibodies Specific for Aβ40 and the Aβ that Ends at Residues Alanine42/Threonine43 (Aβ42)

Amyloid -protein (A) deposits in the cerebral cortices of patients with Alzheimer's disease (AD) were investigated immunohistochemically to determine their carboxy terminal sequences. Antibodies specific for A terminating at residue valine₄₀ (A40) and at residues alanine₄₂/threonine₄₃ (A42) were used. Virtually all parenchymal A deposits were positive for A42. Many of these deposits were also partially or completely labeled for A40. The degree of A40 labeling varied from area to area within a given brain and from AD case to AD case. In contrast to parenchymal deposits, A40 labeled essentially all the vascular deposits which constitute amyloid angiopathy (AA), with A42 occurring variably in some of these deposits. Occasional AA was found, however, in which A42 predominated or was exclusively deposited. Such a diversity of A species, both in brain parenchyma and in AA, suggests that multiple C-terminal processing mechanisms occur in the cell types responsible for these deposits.     

Intrinsic origin of amyloid aggregation: Behavior of histidine (εεε) and (δδδ) tautomer homodimers of Aβ (1–40)

Amyloid-beta protein (Aβ) accumulation in the brain, which is influenced by several factors, is a hallmark of Alzheimer's disease (AD). Despite the important role of histidine in stabilizing the fibrillar structure of the Aβ peptide at neutral pH, the effect of histidine tautomerism on Aβ peptide aggregation is still largely unknown. Histidine is in equilibrium between δ and ε tautomers and there are three histidine residues (H6, H13, and H14) in the Aβ(1–40) peptide. We performed molecular dynamics simulation on (δδδ) and (εεε) histidine tautomers with different initial homodimeric configurations to elucidate structural and aggregation features. Results indicate that (εεε) homodimers have very low propensity or almost no tendency to form β-sheets, whereas (δδδ) dimers predominantly form β-sheets due to interactions between central hydrophobic core (CHC) residues and C-terminal residues. β-sheet formation occurred in the same regions of each dimer chain at the CHC and C-/N- terminals for different configurations of (δδδ). These results suggest that (δδδ) has an important role in AD progression. Our study provides deeper insight into the effect of tautomerism of histidine residues in Aβ(1–40) on amyloid aggregation.     

A review of mechanistic studies on aromatase (CYP19) and 17α-hydroxylase-17,20-lyase (CYP17)

In the conventional P-450 dependent hydroxylation reaction, the Fe(III) resting state of the enzyme, by a single electron transfer, is reduced to Fe(II), which reacts with O(2) to produce a Fe(III)-O-O intermediate. The latter following the transfer of another electron furnishes a ferric-peroxyanion, Fe(III)-O-O(-), which after protonation leads to the fission of the O-O bond resulting in the formation of Fe(V)O, the key player in the hydroxylation process. Certain members of the P-450 family, including CYP17 and CYP19, catalyze, at the same active site, not only the hydroxylation process but also an acyl-carbon bond cleavage reaction which has been interpreted to involve the nucleophilic attack of the ferric-peroxyanion, Fe(III)-O-O(-), on the acyl carbon to furnish a tetrahedral intermediate which fragments, leading to acyl-carbon cleavage. Evidence is presented to show that in the case of CYP17 the attack of Fe(III)-O-O(-) on the target carbon is promoted by cytochrome b(5), which acts as a conformational regulator of CYP17. It is this regulation of CYP17 that provides a safety mechanism which ensures that during corticoid biosynthesis, which involves 17α-hydroxylation by CYP17, androgen formation is avoided. Finally, a brief account is presented of the inhibitors, of the two enzymes, which have been designed on the basis of their mechanism of action. Article from the Special issue on 'Targeted Inhibitors'.     

Macromolecular and small-molecule modulation of intracellular Aβ42 aggregation and associated toxicity

Aβ (amyloid β-peptide) has a central role in AD (Alzheimer's disease) where neuronal toxicity is linked to its extracellular and intracellular accumulation as oligomeric species. Searching for molecules that attenuate Aβ aggregation could uncover novel therapies for AD, but most studies in mammalian cells have inferred aggregation indirectly by assessing levels of secreted Aβ peptide. In the present study we establish a mammalian cell system for the direct visualization of Aβ formation by expression of an Aβ(42)-EGFP (enhanced green fluorescent protein) fusion protein in the human embryonic kidney cell line T-REx293, and use this to identify both macromolecules and small molecules that reduce aggregation and associated cell toxicity. Thus a molecular shield protein AavLEA1 [Aphelenchus avenae LEA (late embryogenesis abundant) protein 1], which limits aggregation of proteins with expanded poly(Q) repeats, is also effective against Aβ(42)-EGFP when co-expressed in T-REx293 cells. A screen of polysaccharide and small organic molecules from medicinal plants and fungi reveals one candidate in each category, PS5 (polysaccharide 5) and ganoderic acid DM respectively, with activity against Aβ. Both PS5 and ganoderic acid DM probably promote Aβ aggregate clearance indirectly through the proteasome. The model is therefore of value to study the effects of intracellular Aβ on cell physiology and to identify reagents that counteract those effects.     

DHPC Strongly Affects the Structure and Oligomerization Propensity of Alzheimer's Aβ(1-40) Peptide

Alzheimer's disease (AD) is thought to depend on the deleterious action of amyloid fibrils or oligomers derived from β-amyloid (Aβ) peptide. Out of various known Aβ alloforms, the 40-residue peptide Aβ(1-40) occurs at highest concentrations inside the brains of AD patients. Its aggregation properties critically depend on lipids, and it was thus proposed that lipids could play a major role in AD. To better understand their possible effects on the structure of Aβ and on the ability of this peptide to form potentially detrimental amyloid structures, we here analyze the interactions between Aβ(1-40) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC). DHPC has served, due to its controlled properties, as a major model system for studying general lipid properties. Here, we show that DHPC concentrations of 8 mM or higher exert dramatic effects on the conformation of soluble Aβ(1-40) peptide and induce the formation of β-sheet structure at high levels. By contrast, we find that DHPC concentrations well below the critical micelle concentration present no discernible effect on the conformation of soluble Aβ, although they substantially affect the peptide's oligomerization and fibrillation kinetics. These data imply that subtle lipid-peptide interactions suffice in controlling the overall aggregation properties and drastically accelerate, or delay, the fibrillation kinetics of Aβ peptide in near-physiological buffer solutions.     

Role of 11β-OH-C(19) and C(21) steroids in the coupling of 11β-HSD1 and 17β-HSD3 in regulation of testosterone biosynthesis in rat Leydig cells

Here we describe further experiments to support our hypothesis that bidirectional 11β-HSD1-dehydrogenase in Leydig cells is a NADP(H) regenerating system. In the absence of androstenedione (AD), substrate for 17β-HSD3, incubation of Leydig cells with corticosterone (B) or several C₁₉- and C₂₁-11β-OH-steroids, in the presence of [³H]-11-dehydro-corticosterone (A), stimulated 11β-HSD1-reductase activity. However, in presence of 30 μM AD, testosterone (Teso) synthesis is stimulated from 4 to 197 picomole/25,000 cells/30 min and concomitantly inhibited 11β-HSD1-reductase activity, due to competition for the common cofactor NADPH needed for both reactions. Testo production was further significantly increased (p < 0.05) to 224-267 picomole/25,000 cells/30 min when 10 μM 11β-OH-steroids (in addition to 30 μM AD) were also included. Similar results were obtained in experiments conducted with lower concentrations of AD (5 μM), and B or A (500 nM).Incubations of 0.3-6.0 μM of corticosterone (plus or minus 30 μM AD) were then performed to test the effectiveness of 17β-HSD3 as a possible NADP⁺ regenerating system. In the absence of AD, increasing amounts (3-44 pmol/25,000 cells/30 min) of 11-dehydro-corticosterone were produced with increasing concentrations of corticosterone in the medium. When 30 μM AD was included, the rate of 11-dehydro-corticosterone formation dramatically increased 1.3-5-fold producing 4-210 pmol/25,000 cells/30 min of 11-dehydro-corticosterone. We conclude that 11β-HSD1 is enzymatically coupled to 17β-HSD3, utilizing NADPH and NADP in intermeshed regeneration systems.     

Abundance and aggregation egg of Aedes aegypti L. and Aedes albopictus (Skuse) (Diptera: Culicidae) in the north and northwest of the State of Paraná, Brazil

The abundance and aggregation of eggs of Aedes aegypti L. and Aedes albopictus Skuse was evaluated in the municipalities of Cambé, Ibipor?, Jacarezinho, Maringá and Paranavaí, in the State of Paraná, Brazil by means of oviposition traps. Of the 225 installed traps, 100 were registered as positive for eggs; 4140 eggs were collected, thus demonstrating an highly aggregate distribution. Both species were registered in Cambé, Jacarezinho, Maringá and Paranavaí. Ae. albopictus was generally less abundant and was not present in Ibipor? nor in the oviposition traps of a second collection of Maringá. The relation between sexes for Ae. aegypti was approximately 1:1. In the comparison of the number of adults collected between the two species, a negative correlation was obtained in the samples of Maringá and Cambé, what was attributed the seasonality of these populations. The coexistence of these species indicates that both are under pressure by the control programs, therefore specific evaluations are necessary.     

Resveratrol protects rats from Aβ-induced neurotoxicity by the reduction of iNOS expression and lipid peroxidation

Alzheimer disease (AD) is an age-dependent neurodegenerative disease characterized by the formation of β-amyloid (Aβ)-containing senile plaque. The disease could be induced by the administration of Aβ peptide, which was also known to upregulate inducible nitric oxide synthase (iNOS) and stimulate neuronal apoptosis. The present study is aimed to elucidate the cellular effect of resveratrol, a natural phytoestrogen with neuroprotective activities, on Aβ-induced hippocampal neuron loss and memory impairment. On adult Sprague-Dawley rats, we found the injection of Aβ could result in a significant impairment in spatial memory, a marked increase in the cellular level of iNOS and lipid peroxidation, and an apparent decrease in the expression of heme oxygenase-1 (HO-1). By combining the treatment with Aβ, resveratrol was able to confer a significant improvement in spatial memory, and protect animals from Aβ-induced neurotoxicity. These neurological protection effects of resveratrol were associated with a reduction in the cellular levels of iNOS and lipid peroxidation and an increase in the production of HO-1. Moreover, the similar neurological and cellular response were also observed when Aβ treatment was combined with the administration of a NOS inhibitor, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME). These findings strongly implicate that iNOS is involved in the Aβ-induced lipid peroxidation and HO-1 downregulation, and resveratrol protects animals from Aβ-induced neurotoxicity by suppressing iNOS production.     

Design,synthesis, and evaluation of 2-piperidone derivatives for the inhibition of β-amyloid aggregation and inflammation mediated neurotoxicity

A series of novel multipotent 2-piperidone derivatives were designed, synthesized and biologically evaluated as chemical agents for the treatment of Alzheimer’s disease (AD). The results showed that most of the target compounds displayed significant potency to inhibit Aβ_1–42 self-aggregation. Among them, compound 7q exhibited the best inhibition of Aβ_1–42 self-aggregation (59.11% at 20 μM) in a concentration-dependent manner. Additionally, the compounds 6b, 7p and 7q as representatives were found to present anti-inflammation properties in lipopolysaccharide (LPS)-induced microglial BV-2 cells. They could effectively suppress the production of pro-inflammatory cytokines such as TNF-α, IL-1β and IL-6. Meanwhile, compound 7q could prevent the neuronal cell SH-SY5Y death by LPS-stimulated microglia cell activation mediated neurotoxicity. The molecular modeling studies demonstrated that compounds matched the pharmacophore well and had good predicted physicochemical properties and estimated IC₅₀ values. Moreover, compound 7q exerted a good binding to the active site of myeloid differentiation factor 88 (MyD88) through the docking analysis and could interfere with its homodimerization or heterodimerization. Consequently, these compounds emerged as promising candidates for further development of novel multifunctional agents for AD treatment.     

Development of β-sheet structure in Aβ aggregation intermediates diminishes exposed hydrophobic surface area and enhances proinflammatory activity

Three decades of research, both in vitro and in vivo, have demonstrated the conformational heterogeneity that is displayed by the amyloid β peptide (Aβ) in Alzheimer's disease (AD). Understanding the distinct properties between Aβ conformations and how conformation may impact cellular activity remain open questions, yet still continue to provide new insights into protein misfolding and aggregation. In particular, there is interest in the group of soluble oligomeric prefibrillar Aβ species comprising lower molecular weight oligomers up to larger protofibrils. In the current study, a number of strategies were utilized to separate Aβ protofibrils and oligomers and show that the smaller Aβ oligomers have a much different conformation than Aβ protofibrils. The differences were consistent for both Aβ40 and Aβ42. Protofibrils bound thioflavin T to a greater extent than oligomers, and were highly enriched in β-sheet secondary structure. Aβ oligomers possessed a more open structure with significant solvent exposure of hydrophobic domains as determined by tryptophan fluorescence and bis-ANS binding, respectively. The protofibril-selective antibody AbSL readily discerned conformational differences between protofibrils and oligomers. The more developed structure for Aβ protofibrils ultimately proved critical for provoking the release of tumor necrosis factor α from microglial cells. The findings demonstrated a dependency on β-sheet structure for soluble Aβ aggregates to cause a microglial inflammatory response. The Aβ aggregation process yields many conformationally-varied species with different levels of β-structure and exposed hydrophobicity. The conformation elements likely determine biological activity and pathogenicity.     

Complement System Activation by Amyloid Aggregates of Aβ(1-40) and Aβ(1-42) Peptides: Facts and Hypotheses

Biophysics - Abstract—Here, we consider the problem of the activation of the complement system by amyloid aggregates, in particular, amyloid fibrils of the Aβ(1-40) and Aβ(1-42)...     

Menadione sodium bisulfite inhibits the toxic aggregation of amyloid-β(1–42)

Protein misfolding and aggregation are associated with amyloidosis. The toxic aggregation of amyloid-β 1–42 (Aβ42) may disrupt cell membranes and lead to cell death and is thus regarded as a contributing factor in Alzheimer's disease (AD). 1,4-naphthoquinone (NQ) has been shown to exhibit strong anti-aggregation effects on amyloidogenic proteins such as insulin and α-synuclein; however, its high toxicity and poor solubility limit its clinical application. Menadione sodium bisulfite (MSB, also known as vitamin K3), is used clinically in China to treat hemorrhagic diseases caused by vitamin K deficiency and globally as a vitamin K supplement. We hypothesized that MSB could inhibit amyloid formation since its backbone structure is similar to NQ. To test our hypothesis, we first investigated the effects of MSB on Aβ42 amyloid formation in vitro. We found that MSB inhibited Aβ42 amyloid formation in a dose dependent manner, delayed the secondary structural conversion of Aβ42 from random coil to ordered β-sheet, and attenuated the ability of Aβ42 aggregates to disrupt membranes; moreover, the quinone backbone rather than lipophilicity is esstial for the inhibitory effects of MSB. Next, in cells expressing a pathogenic APP mutation (Osaka mutation) that results in the formation of intraneuronal Aβ oligomers, MSB inhibited the intracellular aggregation of Aβ. Moreover, MSB treatment significantly extended the life span of Caenorhabditis elegans CL2120, a strain that expresses human Aβ42. Together, these results suggest that MSB and its derivatives may be further explored as potential therapeutic agents for the prevention or treatment of AD.     

Substoichiometric inhibition of Aβ1-40 aggregation by a tandem Aβ40-1-Gly8-1-40 peptide

Aβ peptides aggregate to form insoluble and neurotoxic fibrils associated with Alzheimer’s disease. Inhibition of the aggregation has been the subject of numerous studies. Here we describe a novel, substoichiometric inhibitor of Aβ_1-40 fibrillization as a tandem dimeric construct consisting of Aβ_40-1 (reverse sequence) linked to Aβ_1-40 via an eight residue glycine linker. At molar ratios of the tandem peptide to Aβ_1-40 of 1:10 to 1:25 inhibition of fibrillization, as measured by ThioflavinT, was observed. We postulate that the tandem construct binds to a fibrillar intermediate but the reverse sequence delays or prevents further monomer association.     

Positioning of the Alzheimer Aβ(1–40) peptide in SDS micelles using NMR and paramagnetic probes

NMR spectroscopy combined with paramagnetic relaxation agents was used to study the positioning of the 40-residue Alzheimer Amyloid β-peptide Aβ(1–40) in SDS micelles. 5-Doxyl stearic acid incorporated into the micelle or Mn²⁺ ions in the aqueous solvent were used to determine the position of the peptide relative to the micelle geometry. In SDS solvent, the two α-helices induced in Aβ(1–40), comprising residues 15–24, and 29–35, respectively, are surrounded by flexible unstructured regions. NMR signals from these unstructured regions are strongly attenuated in the presence of Mn²⁺ showing that these regions are positioned mostly outside the micelle. The central helix (residues 15–24) is significantly affected by 5-doxyl stearic acid however somewhat less for residues 16, 20, 22 and 23. This α-helix therefore resides in the SDS headgroup region with the face with residues 16, 20, 22 and 23 directed away from the hydrophobic interior of the micelle. The C-terminal helix is protected both from 5-doxyl stearic acid and Mn²⁺, and should be buried in the hydrophobic interior of the micelle. The SDS micelles were characterized by diffusion and ¹⁵N-relaxation measurements. Comparison of experimentally determined translational diffusion coefficients for SDS and Aβ(1–40) show that the size of SDS micelle is not significantly changed by interaction with Aβ(1–40). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Molecular modeling of the interaction of 17(20)Z- and 17(20)E-pregna-5,17(20)-dien-21-oyl amides with the nuclear receptor LXRβ

Eight isomeric 17(20)Z- and 17(20)E-pregna-5,17(20)-dien-21-oyl amides, conformationally rigid oxysterol analogues, differing in the structure of the amide moiety have been analyzed. Analysis of low energy conformers revealed that all 17(20)E-isomers had three main energy minima (corresponding to the values of the dihedral angle θ_20,21 (C17=C20-C21=O) about ～0°, ～120°, and ～240°); the most occupied minimum corresponded to θ_20,21 about ～0°. 17(20) Z-Isomers had either one or two pools of stable low energy conformations. Molecular docking of these compounds to the ligand-binding site of the nuclear receptor LXRβ (a potential target) demonstrated high probability of binding of E-isomers but not Z-isomers with this target. Results of the molecular modeling were confirmed by an experiment in which stimulation of triglyceride biosynthesis in Hep G2 cells in the presence of 17(20)E-3β-hydroxypregna-5,17(20)-dien-21-oyl (hydroxyethyl)amide was demonstrated.