Pharmacokinetics and Molecular Modeling Indicate nAChRα4-Derived Peptide HAEE Goes through the Blood-Brain Barrier

Abstract

One of the treatment strategies for Alzheimer's disease (AD) is based on the use of pharmacological agents capable of binding to beta-amyloid (Aβ) and blocking its aggregation in the brain. Previously, we found that intravenous administration of the synthetic tetrapeptide Acetyl-His-Ala-Glu-Glu-Amide (HAEE), which is an analogue of the 35-38 region of the α4 subunit of α4β2 nicotinic acetylcholine receptor and specifically binds to the 11-14 site of Aβ, reduced the development of cerebral amyloidogenesis in a mouse model of AD. In the current study on three types of laboratory animals, we determined the biodistribution and tissue localization patterns of HAEE peptide after single intravenous bolus administration. The pharmacokinetic parameters of HAEE were established using uniformly tritium-labeled HAEE. Pharmacokinetic data provided evidence that HAEE goes through the blood-brain barrier. Based on molecular modeling, a role of LRP1 in receptor-mediated transcytosis of HAEE was proposed. Altogether, the results obtained indicate that the anti-amyloid effect of HAEE, previously found in a mouse model of AD, most likely occurs due to its interaction with Aβ species directly in the brain.

Keywords: Alzheimer’s disease; LRP1; beta-amyloid; blood–brain barrier; peptide drug; receptor-mediated transcytosis; α4β2 nicotinic acetylcholine receptor.

Figure 1

Pharmacokinetics of HAEE in rabbit blood after a single intravenous (i.v.) bolus injection at a dose of 120 μg/kg. (A,B). Approximation of experimental data by equations of mono- and bi-exponential decay functions. Data are presented in straight (A) and semi-logarithmic (B) coordinates. (C). Deviation of experimental data from the results predicted by the biexponential decay function in the time range 0–4 min. (D). Calculation of pharmacokinetic parameters in an open two-compartment model for i.v. bolus administration in the time range 4–120 min.

Figure 2

Pharmacokinetics of HAEE in rat blood after a single intravenous bolus injection at doses of 50, 300 and 900 µg/kg. (A,B). Effect of HAEE dose on HAEE pharmacokinetics. Data are presented in straight (A) and semi-logarithmic (B) coordinates. (C). Verification of the linearity of HAEE pharmacokinetics versus the peptide dose. (D). Analysis of the effect of long-term course administration of HAEE on the pharmacokinetics of the peptide.

Figure 3

Distribution of HAEE between organs and tissues of mice after intraperitoneal bolus injection at a dose of 300 μg/kg. (A). Quantity of HAEE in blood and kidneys; (B). quantity of HAEE in the liver, heart, and omentum; (C). quantity of HAEE in the brain.

Figure 4

Interaction of the HAEE tetrapeptide (marked blue for the unprotonated system, marked orange for the protonated system) with the 281-HHVE-284 site (marked pink) of LRP1 after 50 ns (top) and 20 ns (bottom) of MD equilibration.

Figure 5

Results of global docking of the protonated tetrapeptide HAEE (marked orange) to LRP1 (left), and the structure of the model with the initial location of the tetrapeptide relative to the HHVE site after 50 ns MD (right). The HHVE site is marked pink. The bar graph shows the total number of contacts for all docking models for each amino acid residue of LRP1.

Figure 6

Interaction of angiopep-2 (marked green) with mouse LRP1 after 30 ns (left) and 50 ns of MD (right). The KTEE site is marked blue and the HHVE site in LRP1 is marked pink.