Ferrocene tripeptide Gly-Pro-Arg conjugates: Synthesis and inhibitory effects on Alzheimer's Aβ_1-42 fibrillogenesis and Aβ-induced cytotoxicity in vitro

Alzheimer's disease (AD) is the most common cause of dementia, and currently there is no clinical treatment to cure it or to halt its progression. Aggregation and fibril formation of β-amyloid peptides (Aβ) are central events in the pathogenesis of AD. Many efforts have been spent on the development of effective inhibitors to prevent Aβ fibrillogenesis and cause disaggregation of preformed Aβ fibrils. In this study, the conjugates of ferrocene and Gly-Pro-Arg (GPR) tripeptide, Boc-Gly-Pro-Arg(NO ₂)-Fca-OMe (4, GPR-Fca) and Fc-Gly-Pro-Arg-OMe (7, Fc-GPR) (Fc: ferrocene; Fca: ferrocene amino acid) were synthesized by HOBT/HBTU protocol in solution. These ferrocene GPR conjugates were employed to inhibit Aβ_1-42 fibrillogenesis and to disaggregate preformed Aβ fibrils. The inhibitory properties of ferrocene GPR conjugates on Aβ_1-42 fibrillogenesis were evaluated by thioflavin T (ThT) fluorescence assay, and confirmed by atomic force microscopy (AFM) analysis. The interaction between the ferrocene GPR conjugates and Aβ_1-42 was monitored by electrochemical means. Our results showed that both GPR and GPR-Fca can significantly inhibit the fibril formation of Aβ _1-42, and cause disaggregation of the preformed fibrils. As expected, GPR-Fca shows stronger inhibitory effect on Aβ_1-42 fibrillogenesis than that of its parent peptide GPR. In contrast, Fc-GPR shows no inhibitory effect on fibrillogenesis of Aβ_1-42. Furthermore, GPR-Fca demonstrates significantly protection against Aβ-induced cytotoxicity and exhibits high resistance to proteolysis and good lipophilicity.