The effect of the neuroprotector isatin on complex formation of beta-amyloid peptide fragments with some intracellular proteins

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 Aβ_1-42. The aim of this study was to investigate the effect of the neuroprotector isatin (100 mM) 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 Kd values were determined for GAPDH and pyruvate kinase complexes with immobilized Aβ_1-42 and Aβ_25-35. The presence of 100 mM isatin caused a significant (more than fivefold) increase in the Kd 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 Kd) and to a lesser extent with Aβ_12-28 and Aβ_25-35 (a 10-fold increase in Kd). It should be noted that in the presence of isatin the Kd 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).