A single-domain antibody for the detection of pathological Tau protein in the early stages of oligomerization

BACKGROUND

Soluble oligomeric forms of Tau protein have emerged as crucial players in the propagation of Tau pathology in Alzheimer's disease (AD). Our objective is to introduce a single-domain antibody (sdAb) named 2C5 as a novel radiotracer for the efficient detection and longitudinal monitoring of oligomeric Tau species in the human brain.

METHODS

The development and production of 2C5 involved llama immunization with the largest human Tau isoform oligomers of different maturation states. Subsequently, 2C5 underwent comprehensive in vitro characterization for affinity and specificity via Enzyme-Linked Immunosorbent Assay and immunohistochemistry on human brain slices. Technetium-99m was employed to radiolabel 2C5, followed by its administration to healthy mice for biodistribution analysis.

RESULTS

2C5 exhibited robust binding affinity towards Tau oligomers (Kd = 6.280 nM ± 0.557) and to Tau fibers (Kd = 5.024 nM ± 0.453), with relatively weaker binding observed for native Tau protein (Kd = 1791 nM ± 8.714) and amyloid peptide (Kd > 10,000 nM). Remarkably, this SdAb facilitated immuno-histological labeling of pathological forms of Tau in neurons and neuritic plaques, yielding a high-contrast outcome in AD patients, closely mirroring the performance of reference antibodies AT8 and T22. Furthermore, 2C5 SdAb was successfully radiolabeled with 99mTc, preserving stability for up to 6 h post-radiolabeling (radiochemical purity > 93%). However, following intravenous injection into healthy mice, the predominant uptake occurred in kidneys, amounting to 115.32 ± 3.67, 97.70 ± 43.14 and 168.20 ± 34.52% of injected dose per gram (% ID/g) at 5, 10 and 45 min respectively. Conversely, brain uptake remained minimal at all measured time points, registering at 0.17 ± 0.03, 0.12 ± 0.07 and 0.02 ± 0.01% ID/g at 5, 10 and 45 min post-injection respectively.

CONCLUSION

2C5 demonstrates excellent affinity and specificity for pathological Tau oligomers, particularly in their early stages of oligomerization. However, the current limitation of insufficient blood-brain barrier penetration necessitates further modifications before considering its application in nuclear medicine imaging for humans.

Interest of novel N-alkylpyridinium-indolizine hybrids in the field of Alzheimer's disease: Synthesis, characterization and evaluation of antioxidant activity, cholinesterase inhibition, and amyloid fibrillation interference

A small library of molecules combining indolizine and N-alkyl pyridinium was synthesized and evaluated in a multi-target-directed-ligand strategy for Alzheimer's disease (AD) treatment. The new compounds were classified in three series depending on the number of methylene residues linking the two heterocycles (Ind-PyCx with x = 0, 2 or 3). The molecules were synthesized from the corresponding bis-pyridines by two-step formation of the indolizine core including mono-alkylation of pyridine and 1,3-dipolar cycloaddition with an alkylpropiolate. Their activities against AD's key-targets were evaluated in vitro: acetyl- and butyrylcholinesterase (AChE and BChE) inhibition, antioxidant properties and inhibition of amyloid fibril formation. None of the three series showed significant activities against all the targets. The Ind-PyC2 and Ind-PyC3 series are active on eeAChE and hAChE (µM IC₅₀ values). Most of the positively charged molecules from these two series also appeared active against eqBChE, however they lost their activity on hBChE. Comparative molecular modeling of 13 and 15 docked in hAChE and hBChE highlighted the importance of the substituent (p-methoxybenzoyl or methyloxycarbonyl, respectively) located on the indolizine C-3 for the binding. The larger molecule 13 fits more tightly at the active site of the two enzymes than 15 that shows a larger degree of freedom. The Ind-PyC2 and Ind-PyC3 hybrids displayed some antioxidant activity when tested at 750 µg/mL (up to 95% inhibition of DPPH radical scavenging for 10). In both series, most hybrids were also able to interact with amyloid fibers, even if the inhibitory effect was observed at a high 100 µM concentration. The Ind-PyC0 molecules stand out completely due to their spectroscopic properties which prevent their evaluation by Ellman's and ThT assays. However, these molecules showed interesting features in the presence of preformed fibers. In particular, the strong increase in fluorescence of 3 in the presence of amyloid fibers is very promising for its use as a fibrillation fluorescent reporter dye.

Mass and charge distributions of amyloid fibers involved in neurodegenerative diseases: mapping heterogeneity and polymorphism

Characterization by charge detection mass spectrometry of amyloid fibers involved in neurodegenerative diseases: Aβ peptide, tau and α-synuclein.

Heterogeneity and polymorphism are generic features of amyloid fibers with some important effects on the related disease development. We report here the characterization, by charge detection mass spectrometry, of amyloid fibers made of three polypeptides involved in neurodegenerative diseases: Aβ_1–42 peptide, tau and α-synuclein. Beside the mass of individual fibers, this technique enables to characterize the heterogeneity and the polymorphism of the population. In the case of Aβ_1–42 peptide and tau protein, several coexisting species could be distinguished and characterized. In the case of α-synuclein, we show how the polymorphism affects the mass and charge distributions.

COB231 targets amyloid plaques in post-mortem human brain tissue and in an Alzheimer mouse model

Previous works have shown the interest of naturally fluorescent proflavine derivatives to label Abeta deposits in vitro. This study aimed to further characterize the properties of the proflavine 3-acetylamino-6-[3-(propargylamino)propanoyl]aminoacridine (COB231) derivative as a probe. This compound was therefore evaluated on human post-mortem and mice brain slices and in vivo in 18-month-old triple transgenic mice APPswe, PS1M146V and tauP301L (3xTgAD) mice presenting the main characteristics of Alzheimer's disease (AD). COB231 labelled amyloid plaques on brain slices of AD patients, and 3xTgAD mice at 10 and 0.1 μM respectively. However, no labelling of the neurofibrillary tangle-rich areas was observed either at high concentration or in the brain of fronto-temporal dementia patients. The specificity of this mapping was attested in mice using Thioflavin S and IMPY as positive controls of amyloid deposits. After intravenous injection of COB231 in old 3xTgAD mice, fluorescent amyloid plaques were detected in the cortex and hippocampus, demonstrating COB231 blood–brain barrier permeability. We also controlled the cellular localization of COB231 on primary neuronal cultures and showed that COB231 accumulates into the cytoplasm and not into the nucleus. Finally, using a viability assay, we only detected a slight cytotoxic effect of COB231 (< 10%) for the highest concentration (100 μM).

Disruption of Fibers from the Tau Model AcPHF6 by Naturally Occurring Aurones and Synthetic Analogues

The formation of tau aggregates is strongly linked to the neurodegenerative process in tauopathies such as Alzheimer's disease (AD). Yet only a few molecules have shown to efficiently prevent the in vitro formation of those aggregates, and the identification of such molecules is still an ongoing interest in a therapeutic context. Herein, we report the in vitro evaluation of a series of aurones against the fibrillation of the tau-derived hexapeptide AcPHF6 model. Using thioflavin T-based fluorescence assays, circular dichroism and atomic force microscopy, we showed that aurones are capable of efficiently interacting with the tau-derived hexapeptide. Importantly, this work reveals a significant activity observed for polyhydroxylated aurones. In particular, aurone 23 displayed an almost complete inhibition of fibers formation as shown by AFM at a peptide/inhibitor 1:1 ratio. It is similar to that observed for myricetin, a polyphenolic compound, well-known to prevent the in vitro elongation of tau fibers. Moreover, a tetrahydroxylated isomer, compound 24, was shown as a chemical probe of fibers rather than an inhibitor. Consequently, these results highlight aurones as a new promising scaffold to interfere with tau aggregation for both treatment and diagnosis of AD.

Selective, direct detection of acetylcholine in PBS solution, with self-assembled fluorescent nano-particles: experiment and modelling

Self-assembled nano-particles of a new cyclotriveratrylene discriminate acetylcholine from choline in physiological buffer solution.

‘Clickable’ 2,5-diketopiperazines as scaffolds for ligation of biomolecules: their use in Aβ inhibitor assembly

The synthesis of 1,3,6-trisubstituted-2,5-diketopiperazine scaffolds bearing up to three ‘clickable’ sites for further oxime bond or alkyne–azide cycloaddition ligations is described.

A multimeric quinacrine conjugate as a potential inhibitor of Alzheimer's beta-amyloid fibril formation

Amyloid formation and accumulation of the amyloid beta-peptide (Abeta) in the brain is associated with Alzheimer's disease (AD) pathogenesis. Therefore, among the therapeutic approaches in development to fight the disease, the direct inhibition of the Abeta self-assembly process is currently widely investigated and is one of the most promising approaches. In this study we investigated the potential of a multimeric display of quinacrine derivatives, as compared to the monomer quinacrine, as a design principal for a novel class of inhibitors against Abeta fibril formation. The presented multimeric conjugate exhibits a cluster of four quinacrine derivatives on a rigid cyclopeptidic scaffold. Herein is reported the synthesis of the conjugate, together with the in vitro inhibitory evaluation of Abeta(1-40) fibrils using the thioflavin T fluorescence assay, and imaging with atomic force microscopy. Our data show that the multimeric compound inhibits Abeta(1-40) fibril formation with an IC(50) value of 20+/-10 microM, which contrasts with the nonactive monomeric analogue. This work suggests that assembling multiple copies of acridine moieties to a central scaffold, for multiple interactions, is a promising strategy for the engineering of inhibitors against Abeta fibril formation.

Concise synthesis of 2-amino-4(3H)-quinazolinones from simple (Hetero)aromatic amines

A novel and simple method of preparation of 2-alkylaminoquinazolin-4-ones with fused heteroaromatic rings from easily accessible (hetero)aromatic amines is described. The method is very efficient, and the 2-alkylaminoquinazolinone derivatives are obtained in three steps without chromatographic purification. The key step is the ring closure of the N-protected guanidine intermediates by intramolecular Friedel-Craft's type substitution.

Chemoselective Assembly and Immunological Evaluation of Multiepitopic Glycoconjugates Bearing Clustered Tn Antigen as Synthetic Anticancer Vaccines

In this paper we investigated the use of regioselectively addressable functionalized templates (RAFTs) as new scaffolds for the design of anticancer vaccine candidates. We report the synthesis of well-defined multiepitopic RAFT scaffolds and their immunological evaluation. These conjugates exhibit clustered Tn analogue as tumor-associated carbohydrate antigen (TACA, B-cell epitope) and the CD4+ helper T-cell peptide from the type 1 poliovirus. The saccharidic and peptidic epitopes were both synthesized separately and combined regioselectively to the RAFT core using a sequential oxime bond formation strategy. B- and T-antigenicity and immunogenicity of the vaccine candidates were investigated in vitro and in vivo. These studies clearly demonstrate that the saccharidic part of the conjugates is recognized by Tn-specific monoclonal antibodies. Moreover, the antibodies elicited by immunization of mice with our vaccine candidates recognize the native form of Tn epitope expressed on human tumor cells. Together with oxime ligation technique, these results suggest that the RAFT scaffold provides a promising and suitable tool for engineering potent synthetic anticancer vaccine.

A case study of 2,2-dimethylthiazolidine as locked cis proline amide bond: synthesis, NMR and molecular modeling studies of a δ-conotoxin EVIA peptide analog

The delta-conotoxin EVIA from the Conus ermineus venom, a recently characterized toxin, exhibits cis-trans isomerism of the Leu12-Pro13 bond associated with the triggering of its biological activity. In this paper we use the pseudoproline concept to target the presumed bioactive cis conformation. We report the design and the synthesis of loop 2 analogs from residue 8 to 18 containing either the cis-inducing Cys(PsiMe,MePro)13 unit or the natural proline residue. NMR studies in water and molecular modeling allowed us to identify the amide bond "locked" in a cis conformation for as in the suggested bioactive form of the natural toxin.

Effects of cognitive-behavioural therapy on health-related quality of life in obese subjects with and without binge eating disorder

OBJECTIVE

To measure the effects of cognitive-behavioural therapy on health-related quality of life (HRQL) in obese patients, in relation to binge eating disorder.

DESIGN

Longitudinal, clinical intervention study consisting of structured sessions of cognitive-behavioural therapy, preceded by sessions chaired by a psychologist in subjects with binge eating.

SUBJECTS

Two groups of obese patients (92 treated by cognitive-behavioural therapy (77 females); 76 untreated controls (67 female), selected from the waiting list (control group)). Of 92 treated patients, 46 had a binge eating disorder at psychometric testing and structured clinical interview.

MEASUREMENTS

Health-related quality of life by means of Short-Form 36 questionnaire at baseline and after 3-5 months.

RESULTS

Cognitive-behavioural treatment produced an average weight loss of 9.4+/-7.5 kg, corresponding to a BMI reduction of 3.48+/-2.70 kg/m(2). No changes were observed in the control group. All scales of HRQL improved in treated subjects (by 5-19%). In obese subjects with binge eating weight loss was lower in comparison to non-bingers (7.7+/-8.1 vs 11.1+/-6.6; P=0.034). However, the improvement in HRQL was on average larger, and significantly so for Role Limitation-Physical (P=0.006), Role Limitation-Emotional (P=0.002), Vitality (P=0.003), Mental Health (P=0.032) and Social Functioning (P=0.034). Bodily Pain was the sole scale whose changes paralleled changes in body weight.

CONCLUSIONS

The positive effects of cognitive-behavioural therapy, mainly in subjects with binge eating, largely outweigh the effects on body weight, resulting in a significant change in self-perceived health status.

A FTIR spectroscopy evidence of the interactions between wheat germ agglutinin and N-acetylglucosamine residues

Wheat germ agglutinin (WGA), a lectin binding a N-acetyl-D-neuraminic acid (NeuNAc) and/or N-acetyl-D-glucosamine (GlcNAc) group, was studied by Fourier transform infrared (FTIR) spectroscopy. Deconvolution of the FTIR spectrum of WGA alone indicated the presence of few alpha-helices and beta-sheets, in contrast to many other lectins. These results agree with previous WGA crystal data. The WGA conformational changes, induced by GlcNAc-bearing liposomes or GlcNAc oligomers, were studied by infrared differential spectroscopy. The GlcNAc binding to WGA resulted in a decrease of turns and alpha-helices and a concomitant appearance of beta-sheets, inducing more or less peptidic N-H deuteration.