Inhibition of β-amyloid1-40 Peptide Aggregation and Neurotoxicity by Citrate

The accumulation of beta-amyloid (A beta) aggregates is a characteristic of Alzheimer's disease (AD). Furthermore, these aggregates have neurotoxic effects on cells, and thus, molecules that inhibit A beta aggregate formation could be valuable therapeutics for AD. It is well known that aggregation of A beta depends on its hydrophobicity, and thus, in order to increase the hydrophilicity of A beta, we considered using citrate, an anionic surfactant with three carboxylic acid groups. We hypothesized that citrate could reduce hydrophobicity and increase hydrophilicity of A beta(1-40) molecules via hydrophilic/electrostatic interactions. We found that citrate significantly inhibited A beta(1-40) aggregation and significantly protected SH-SY5Y cell line against A beta(1-40) aggregates-induced neurotoxicity. In details, we examined the effects of citrate on A beta(1-40) aggregation and on A beta(1-40) aggregates-induced cytotoxicity, cell viability, and apoptosis. Th-T assays showed that citrate significantly inhibited A beta(1-40) aggregation in a concentration-dependent manner (Th-T intensity: from 91.3% in 0.01 mM citrate to 82.1% in 1.0 mM citrate vs. 100.0% in A beta(1-40) alone). In cytotoxicity and viability assays, citrate reduced the toxicity of A beta(1-40) in a concentration-dependent manner, in which the cytotoxicity decreased from 107.5 to 102.3% as compared with A beta(1-40) aggregates alone treated cells (127.3%) and the cell viability increased from 84.6 to 93.8% as compared with the A beta(1-40) aggregates alone treated cells (65.3%). Furthermore, Hoechst 33342 staining showed that citrate (1.0 mM) suppressed A beta(1-40) aggregates-induced apoptosis in the cells. This study suggests that citrate can inhibit A beta(1-40) aggregation and protect neurons from the apoptotic effects of A beta(1-40) aggregates. Accordingly, our findings suggest that citrate administration should be viewed as a novel neuroprotective strategy for AD.