RAISING AVAILABLE BRAIN CONCENTRATIONS OF A POTENTIAL ALZHEIMER’S DISEASE DRUG CANDIDATE BY PEPTIDE CYCLIZATION

Abstract

Alzheimer’s disease (AD) is a widespread progressive neurodegenerative disease but to date, no curative treatment is established. To target toxic amyloid-beta (Aβ) species and to convert them into non-toxic species, we have developed and designed D-enantiomeric peptides. Here, we investigated if intraperitoneal and intravenous administration of a cyclic D-enantiomeric peptide (cycP) result in increased brain and plasma concentrations compared to the equivalent linear D-peptide (linP) which has been characterized before (Leithold et al., 2016). Furthermore, cycP’s pharmacokinetic profile, proteolytic stability and plasma protein binding properties were characterized to investigate whether cycP is a potential drug candidate. To determine cycP’s concentration-time-profile in murine plasma and brain, 3H-labelled peptide was administered intraperitoneally, intravenously and orally to wildtype mice (male C57BL/6N, 12 weeks). Proteolytic stability was investigated by thin layer chromatography after incubation for up to seven days in murine plasma, brain-homogenate and human liver microsomes. Plasma protein binding to human serum albumin (HSA) and α1-acid glycoprotein (AGP) was examined with TRANSIL Binding Kits. Four hours after intraperitoneal or intravenous administration, cycP concentrations in the brain were up to ten times higher than linP concentrations. In plasma, cycP concentrations were up to eight times higher. Furthermore, cycP showed longer half-life in plasma than linP. Oral cycP administration resulted in a constant concentration-time-profile. Brain concentrations of cycP after oral administration were even higher between 4 and 24 hours than those after i.p. or i.v. administration. Using thin layer chromatography we could show that cycP was not degraded within seven days. Plasma protein binding of cycP was stronger to AGP (dissociation constant [KD]: 1.2 μM, fraction unbound [fu]: 6 %) than to HSA (KD: 33 μM, fu: 5 %). As cycP concentrations in the brain were considerably higher than those of linP, cycP seems to pass the blood brain barrier (BBB) more efficiently than linP. This is fundamental for an Aß-targeting drug, as Aß is mainly found in AD-patients’ brains. In fact, an increased mobility to pass the BBB probably allows administration of lower doses for cycP treatment as compared to linP treatment, reducing further the risk of adverse side effects.