Memantine and Amantadine KLVFF peptide conjugates: Synthesis, structure determination, amyloid-β interaction and effects on recognition memory in mice

Background: Adamantane derivatives, such as memantine (Mem) and amantadine (Ada), have distinct mechanisms and therapeutic applications. Ada is primarily utilized as an antiviral and anti-Parkinson drug without significant pro-cognitive effects, Mem is effective in various clinical conditions characterized by cognitive deficits, including Alzheimer's disease. Recent evidence highlights a neuroprotective role for Aβ monomers, suggesting that preventing their aggregation into toxic oligomers could be a promising therapeutic strategy. Based on the observation that the Lys-Leu-Val-Phe-Phe (KLVFF) peptide, can block the transition of randomly coiled Aβ monomers into toxic β-sheet aggregates, two KLVFF conjugates, the Mem-Succ-KLVFF and Ada-Succ-KLVFF were investigated. Methods: Peptides were synthesized by Microwave-Assisted Solid Phase Peptide Synthesis (MW-SPPS). Circular Dichroism (CD), Th-T fluorescence and Gel-Electrophoresis techniques were used to assess the inhibitory effect on Aβ42 fibrillogenesis. The formation of inclusion complexes with β-Cyclodextrin (β-CyD) was demonstrated by NMR Spectroscopy. The Novel Object Recognition (NOR) test, followed by double-blind analysis, was applied for in vivo response to compounds administration. In vitro effects on neurons were studied by MTT assay and WB analysis, whereas HR ESI-MS allowed the molecular detection on brain homogenates. Results: These compounds differently affect Aβ42 aggregation. Mem-Succ-KLVFF, and Succ-KLVFF affect pCREB levels in differentiated SH-SY5Y, a signaling pathway involved in memory processes. In the NOR test, both Mem and KLVFF exhibited pro-cognitive effects individually and synergistically when co-administered. Conclusion: Structure-activity relationships are discussed, integrating in vivo results, memory-related cellular pathways, and HR-ESI-MS analyses. These findings support the therapeutic potential of these compounds in preserving cognitive function.