Study of the effect of ascorbic acid on Aβ42 peptide aggregation

Abstract

AbstractBackgroundAscorbic acid (AA) is an antioxidant molecule found at high concentrations in the brain. A negative correlation was found in Alzheimer’s disease (AD) patients between the decrease in AA brain levels and the accumulation of amyloid plaques indicating that AA plays some function in amyloid aggregation, however, no studies have elucidated its mechanism of action so far, which can greatly contribute to the development of new therapeutic strategies for AD.MethodTo investigate AA as inhibitor of amyloid aggregation, amyloid‐beta 1‐42 (Aβ42) samples containing or not AA were incubated in pro‐aggregation conditions and analyzed by atomic force microscopy (AFM) and fluorescence spectroscopy using Thioflavin T. The mechanism of action presented by AA was evaluated using isothermal titration calorimetry (ITC) technique to investigate its binding to Aβ42 monomers.ResultFluorescence analyses pointed out to a decrease in fibril formation for samples incubated with AA at a concentration found in brains of healthy patients. After 72 h, these samples presented almost 80% fewer β‐sheet structures than samples without the antioxidant molecule. The fluorescence results were corroborated by AFM images, indicating that AA inhibited the amyloid aggregation in the fibrillar form. ITC measurements showed a negative cooperative binding between AA and Aβ42 monomers. In this interaction model for multiple sites, the binding of AA molecule in the first site of Aβ42 decreases the affinity constant (Kd) for the binding in the second site (Kd1>Kd2).ConclusionOur study revealed that ascorbic acid is able to inhibit the aggregation of Aβ42 peptides into fibrils through the direct binding to the monomers. Based on the thermodynamic parameters, we observed that the interaction is spontaneous and exothermic. This finding highlights ascorbic acid as a potential candidate for Alzheimer’s disease treatment and the mechanism of action provides novel insights for the inhibition of amyloid aggregation.