The Effect of The Neuroprotector Isatin on Complex Formation of Beta-Amyloid Peptide Fragments with Some Intracellular Proteins

Abstract

Amyloid-β peptide (1−42) (Aβ_1-42) is a key player in the development and progression of Alzheimer’s disease (AD) and related pathologies, determined by formation of protein aggregates in the central nervous system. Aβ_1-42 binding to crucial intracellular targets (and their subsequent inactivation) obviously represents one of the earliest events preceding extracellular pathogenic oligomerization/aggregation of Aβ_1-42. It is reasonable to expect that dissociation of the Aβ_1-42 complexes with intracellular proteins by means of inhibitors followed by subsequent degradation of Aβ_1-42 would not only protect critically important proteins but also prevent intracellular accumulation of Аβ_1-42. The aim of this study was to investigate the effect of the neuroprotector isatin (100 µM) on interaction of known Aβ-binding proteins, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and pyruvate kinase, with Aβ_1-42 and its fragments (Aβ_1-28, Aβ_12-28, Aβ_25-35). Aβ_1-42 and its fragments (Aβ_1-28, Aβ_12-28, Aβ_25-35) immobilized on the Biacore optical biosensor chip interacted with GAPDH and pyruvate kinase. The lowest and basically equal K_d values were determined for GAPDH and pyruvate kinase complexes with immobilized Aβ_1-42 and Aβ_25-35. The presence of 100 µM isatin caused a significant (more than fivefold) increase in the K_d values for GAPDH complexes with all Aβ peptides except Aβ_1-28. In contrast to GAPDH isatin increased dissociation of pyruvate kinase complexes only with Aβ_1-42 (causing a 30-fold increase in K_d) and to a lesser extent with Aβ_12-28 and Aβ_25-35 (a 10-fold increase in the K_d value). It should be noted that in the presence of isatin the K_d values for GAPDH and pyruvate kinase complexes with all Aβ studied were in a narrower concentration range (10^–7 M–10⁻⁶ M) than in the absence of this neuroprotector (10^–8 M–10^–6 M). Data obtained suggest existence of principal possibility of (pharmacological) protection of crucial intracellular targets against both Aβ_1-42, and its aggressive truncated peptides (Aβ_25-35).