(R)‐α‐trifluoromethylalanine containing short peptide in the inhibition of amyloid peptide fibrillation

Abstract

The extracellular deposition of insoluble amyloid fibrils resulting from the aggregation of the amyloid-β (Aβ) is a pathological feature of neuronal loss in Alzheimer's disease (AD). Numerous small molecules have been reported to interfere with the process of Aβ aggregation. Compounds containing aromatic structures, hydrophobic amino acids and/or the α-aminoisobutyric acid (Aib) as β-sheet breaker elements have been reported to be effective inhibitors of Aβ aggregation. We synthesized two peptides, one containing the Aib amino acid and the other including its trifluoromethylated analog (R)-α-Trifluoromethylalanine ((R)-Tfm-Alanine) and we evaluated the impact of these peptides on Aβ amyloid formation. The compounds were tested by standard methods such as thioflavin-T fluorescence spectroscopy and transmission electron microscopy but also by circular dichroism, liquid state nuclear magnetic resonance (NMR) and NMR saturation transfer difference (STD) experiments to further characterize the effect of the two molecules on Aβ structure and on the kinetics of depletion of monomeric, soluble Aβ. Our results demonstrate that the peptide containing Aib reduces the quantity of aggregates containing β-sheet structure but slightly inhibits Aβ fibril formation, while the molecule including the trifluoromethyl (Tfm) group slows down the kinetics of Aβ fibril formation, delays the random coil to β-sheet structure transition and induces a change in the oligomerization pathway. These results suggest that the hydrophobic Tfm group has a better affinity with Aβ than the methyl groups of the Aib and that this Tfm group is effective and important in preventing the Aβ aggregation.

Elucidating the Inhibitory Potential of Designed Peptides Against Amyloid Fibrillation and Amyloid Associated Cytotoxicity

“…The kinetic curve possesses a lag-phase of 5 h, after which fluorescence started to increase in an exponential manner and achieved the stationary phase at 24 h. Our results showed that P4 decreased the final fluorescence intensity by a factor of ≈5.6 and increased the time to attain the plateau. This indicates that P4 executed its anti-amyloidgenic effect by altering the rate of fibril formation of insulin (Botz et al, 2015 ). In contrary, P5 decreased the final fluorescence intensity by a factor of ≈2.5 (almost half as compared with P4) and had insignificant effect on the time to attain the plateau phase.…”

Probing the Outstanding Local Hydrophobicity Increases in Peptide Sequences Induced by Incorporation of Trifluoromethylated Amino Acids

“…We recently compared the potency of a short ( R )‐ or ( S )‐ α‐trifluoromethylalanine‐containing peptide and its nontrifluoromethylated counterpart for the inhibition of amyloid peptide fibrillation. We hypothesized that the better affinity of the trifluoromethylated peptide for Aβ‐amyloid was the result of enhanced hydrophobic interactions . Looking for experimental evidence, we realized that experimentally derived quantitative data about hydrophobicity measurements of fluorinated amino acids or peptides are scarce and that most hydrophobicity assessments originate from computational fragment methods developed by Leo .…”

Fluorinated Molecules and Nanotechnology: Future ‘Avengers’ against the Alzheimer’s Disease?

“…The thioflavin T (ThT) binding assay showed that two of the fluorinated peptides (LVFfFD-PEG and LVfFFD-PEG) are able to delay the aggregation of the Aβ 42 by 1.5 h and 3.1 h. The authors proposed that the position of the fluorine at the extremity of the conjugate seems to influence the hydrophobicity of the sequence. Botz et al [57] synthesized two peptides, one containing the trifluoromethylated (Tfm) analogue (R)-α-trifluoromethylalanine ( Figure 2C) and the other incorporating the nonfluorinated analogue α-aminoisobutyric (Aib). The in vitro studies of these two peptides were evaluated and compared using fluorescence spectroscopy (thought the ThT assay), circular dichroism (CD), and liquid state nuclear magnetic resonance (NMR) for the inhibition of Aβ aggregation.…”