Inhibition of Amyloid Fibril Formation and Cytotoxicity by Hydroxyindole Derivatives

Abstract

Gaining insight into the mechanism of amyloid fibril formation, the hallmark of multiple degenerative syndromes of unrelated origin, and exploring novel directions of inhibition are crucial for preventing disease development. Specific interactions between aromatic moieties were suggested to have a key role in the recognition and self-assembly processes leading to the formation of amyloid fibrils by several amyloidogenic polypeptides, including the beta-amyloid polypeptide associated with Alzheimer's disease. Our finding of the high-affinity molecular recognition and intense amyloidogenic potential of tryptophan-containing peptide fragments led to the hypothesis that screening for indole derivatives might lead to the identification of potential inhibitors of amyloid formation. Such inhibitors could mediate specific recognition processes without allowing further growth of the well-ordered amyloid chain. Using fluorescence spectroscopy, atomic force microscopy, and electron microscopy to screen 29 indole derivatives, we identified three potent inhibitors: indole-3-carbinol (I3C), 3-hydroxyindole (3HI), and 4-hydroxyindole (4HI). The latter, a simple low-molecular weight aromatic compound, was the most effective, completely abrogating not only the formation of aggregated structures by Abeta but also the cytotoxic activity of aggregated Abeta toward cultured cells. The results of this study provide further experimental support for the paradigm of amyloid inhibition by heteroaromatic interaction and point to indole derivatives as a simple molecular platform for the development of novel fibrillization inhibitors.

Disordered Binding of Small Molecules to Aβ(12–28)

“…Normalized by their propensity to bind A␤ (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28), the indole-containing inhibitors NQTrp (see supplemental Table S1) and D Trp-Aib exert the largest effect in this regard. Indole groups have been heavily implicated in A␤ aggregation inhibitor design (39) and were also analyzed in systematic fashion as inhibitors of hen egg white lysozyme aggregation (41). Interestingly, the inhibitor is not required to interact directly with the polar residues mentioned but can act indirectly or allosterically.…”

“…Several therapeutic strategies have been suggested for blocking key steps in the amyloid aggregation proc-ess, including the direct inhibition of aggregation by using either peptides or small molecules (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38). As an example, indole derivatives inhibited fibril formation of A␤ peptide (39,40) and lysozyme (41). Anthraquinones were shown to be inhibitors of Tau protein (42) and A␤40 aggregation (37), and hybrid molecules bearing both indole and quinone rings have been effective in the recovery of a fly model of AD (43).…”

The β-cell assassin: IAPP cytotoxicity

“…Many of these have been developed and tested both on aggregation and cytotoxicity in vitro and in some cases administered to hIAPP transgenic animals with some degrees of successful inhibition of amyloidosis (Westermark & Grimelius 1973, Scrocchi et al 2002, Potter et al 2009, Wang et al 2014, Wijesekara et al 2015, Sivanesam et al 2016. Investigating the mechanism of action of some of these inhibitory compounds has been useful in providing information on the mechanisms of refolding and fibrillogenesis (Cohen et al 2006, Young et al 2014. However, although many of these compounds have been tested in mice, not all of them would be suitable for clinical use.…”

Searching for an endogenous anti-Alzheimer molecule: identifying small molecules in the brain that slow Alzheimer disease progression by inhibition of β-amyloid aggregation

“…After 3 days, solutions were analyzed following the procedure of Cohen and colleagues 26 for TEM analysis. A 10 μL sample was placed on a 400 mesh copper grid covered by carbon-stabilized Formvar film and allowed to stand for 1.5 minutes.…”