Aggregation
of amyloid-β (Aβ) protein stimulated by
Cu<sup>2+</sup> has been recognized as a crucial step in the neurodegenerative
process of Alzheimer’s disease. Hence, it is of significance
to develop bifunctional agents capable of inhibiting Aβ aggregation
as well as Cu<sup>2+</sup>-mediated Aβ toxicity. Herein, a novel
bifunctional nonapeptide, carnosine-LVFFARK-NH<sub>2</sub> (<i>Car</i>-LK7), was proposed by integrating native chelator carnosine
(<i>Car</i>) and an Aβ aggregation inhibitor, Ac-LVFFARK-NH<sub>2</sub> (LK7). Results revealed the bifunctionality of <i>Car</i>-LK7, including remarkably enhanced inhibition capability on Aβ
aggregation as compared to LK7 and a moderate Cu<sup>2+</sup> chelating
affinity (<i>K</i><sub>D</sub> = 28.2 ± 2.1 μM)
in comparison to the binding affinity for Aβ<sub>40</sub> (<i>K</i><sub>D</sub> = 1.02 ± 0.13 μM). The moderate
Cu<sup>2+</sup> affinity was insufficient for <i>Car</i>-LK7 to sequester Cu<sup>2+</sup> from Aβ<sub>40</sub>-Cu<sup>2+</sup> species, but it was sufficient to form ternary Aβ<sub>40</sub>-Cu<sup>2+</sup>-<i>Car</i>-LK7 complexes. Formation
of the ternary complexes directed the aggregation into small, unstructured
aggregates with little β-sheet structure. <i>Car</i>-LK7 also showed higher activity on arresting Aβ<sub>40</sub>-Cu<sup>2+</sup>-catalyzed reactive oxygen species production than <i>Car</i>. Cell viability assays confirmed the prominent protection
activity of <i>Car</i>-LK7 against Cu<sup>2+</sup>-mediated
Aβ<sub>40</sub> cytotoxicity; <i>Car</i>-LK7 could
almost eliminate Aβ<sub>40</sub> cytotoxicity at an equimolar
dose (cell viability increased from 59% to 99%). The research has
thus provided new insight into the design of potent bifunctional agents
against metal-mediated amyloid toxicity by conjugating moderate metal
chelators and existing inhibitors