ИСТИНА

Alzheimer’s disease (AD) is the most prevalent neurological disorder affecting tens of millions of people worldwide. According to the amyloid cascade hypothesis, the key event of the AD pathology is a transition of amyloid-β (Aβ, the 39–42 amino acid long peptide) from the monomeric to the aggregated state, which triggers a chain of adverse molecular events [1]. Various biophysical and biochemical techniques are currently employed to study Aβ peptide, its isoforms and their aggregation in vitro in a search for a cure for AD. Among them, the direct electrochemistry appears to present itself as a rapid and cost-effective approach [2]. It is generally accepted that Aβ electroactivity is determined by oxidation of three types of amino acid residues: Tyr-10, His (His-6, -13 and -14), and Met-35 [3]. The oxidation of Aβ via Tyr-10 at 0.6–0.7 V (vs. Ag/AgCl) commonly utilizes for Aβ detection and for monitoring Aβ aggregation. Thus, the electrochemical approach for studying Aβ seems to be limited to the Tyr-containing peptides. However, as been shown by our group, nearly all proteinogenic amino acids (with a single exception of Glu) exhibit the site-specific electrooxidation in amperometric flow injection analysis (FIA) at a constant potential (0.95 V) on carbon screen printed electrodes (SPE) [4]. Furthermore, Prussian Blue (PB) was found to catalyzed this electrooxidation [4]. For 20 amino acids out of 21 tested, the electrogenerated Berlin Green (BG) has been reduced back to PB by amino acids, forming a catalytic cycle that resulted in an enhancement of oxidation signals. The most effective catalysis – the 54-, 31-, and 11-fold current enhancement – was observed for Gln, Ser, and His, respectively. The significant catalytic effect of electrogenerated BG on their oxidation has been observed for various proteins as well [4]. The aim of this work was to evaluate the effect of PB on the electrochemical oxidation of peptides of various lengths and amino acid sequences. For this purpose, a set of Aβ peptides and its isoforms / mutants was tested on bare and PB modified carbon SPE by cyclic voltammetry and FIA. To our surprise, a pronounced catalytic effect of PB (about a 20-fold current increase) was found for peptides lacking the Tyr residue, viz. Aβ7-D7H, rat Aβ16, and Aβ16-Y10A, while practically no effect of PB was observed for Aβ16-D7H, Aβ16-H6R, and Aβ16-E11A mutants. Only a 1.5-fold current enhancement was observed for Aβ16 oxidation on SPE/PB, compared to bare SPE, by FIA. Apparently, this reflects the fact that no significant catalytic effect of PB was found for Tyr [4]. Therefore, the combination of FIA and SPE/PB opens a new avenue for electrochemical monitoring of aggregation of Aβ isoforms / mutants containing no Tyr residues as well as other peptides of interest, lacking intrinsically electroactive residues. This work was financially supported by the Russian Science Foundation, grant 19-74-30007. References: 1 J. Hardy, N. Bogdanovic, B. Winblad, E. Portelius, N. Andreasen, A. Cedazo-Minguez and H. Zetterberg, J. Intern. Med., 2014, 275, 296-303. 2 A. Veloso, K. Kerman, Anal. Bioanal. Chem., 2013, 405, 5725-5741. 3 E.V. Suprun, S.A. Khmeleva, S.P. Radko, S.A. Kozin, A.I. Archakov and V.V. Shumyantseva, Electrochem. Commun., 2016, 65, 53-56. 4 E.V. Suprun, E.V. Karpova, S.P. Radko and A.A. Karyakin, Electrochim. Acta, 2020, 331, 135289.