β-Sheet breaker peptide inhibitor of Alzheimer's amyloidogenesis with increased blood-brain barrier permeability and resistance to proteolytic degradation in plasma

Short synthetic peptides homologous to the central region of Aβ but bearing proline residues as β-sheet blockers have been shown in vitro to bind to Aβ with high affinity, partially inhibit Aβ fibrillogenesis, and redissolve preformed fibrils. While short peptides have been used extensively as therapeutic drugs in medicine, two important problems associated with their use in central nervous system diseases have to be addressed: (a) rapid proteolytic degradation in plasma, and (b) poor blood-brain barrier (BBB) permeability. Recently, we have demonstrated that the covalent modification of proteins with the naturally occurring polyamines significantly increases their permeability at the BBB. We have extended this technology to iAβ11, an 11-residue β-sheet breaker peptide that inhibits Aβ fibrillogenesis, by covalently modifying this peptide with the polyamine, putrescine (PUT), and evaluating its plasma pharmacokinetics and BBB permeability. After a single intravenous bolus injection in rats, both ¹²⁵I-YiAβ11 and ¹²⁵I-PUT- YiAβ11 showed rapid degradation in plasma as determined by trichloroacetic acid (TCA) precipitation and paper chromatography. By switching to the all D- enantiomers of YiAβ11 and PUT-YiAβ11, significant protection from degradation by proteases in rat plasma was obtained with only 1.9% and 5.7% degradation at 15 min after intravenous bolus injection, respectively. The permeability coefficient x surface area product at the BBB was five- seven- fold higher in the cortex and hippocampus for the ¹²⁵I-PUT-D-YiAβ11 compared to the ¹²⁵I-D-YiAβ11, with no significant difference in the residual plasma volume. In vitro assays showed that PUT-D-YiAβ11 retains its ability to partially inhibit Aβ fibrillogenesis and dissolve preformed amyloid fibrils. Because of its five, to seven-fold increase in permeability at the BBB and its resistance to proteolysis in the plasma, this polyamine- modified β-sheet breaker peptide may prove to be an effective inhibitor of amyloidogenesis in vivo and, hence, an important therapy for Alzheimer's disease.