Effect of natural antioxidants on the aggregation and disaggregation of beta-amyloid

Purpose: To examine the relationship between higher antioxidant activity and aggregation or disaggregation of beta-amyloid (A beta) for 21 plants. Methods: Twenty-nine natural plant extracts and their antioxidant activities were analyzed using DPPH assay. The aggregation and disaggregation of A beta were analyzed using Thioflavin-T assay. Results: Eleven plant extracts exhibited high antioxidant activities with the half-maximal inhibitory concentration (IC50) values < 20.0 mu g/mL. Furthermore, the plant extracts efficiently inhibited A beta aggregation with a mean IC50 value of 17.0 mu g/mL. However, four plant extracts exhibiting low antioxidant activities (IC50 > 80.0 mu g/mL) inhibited A beta aggregation less efficiently with a mean IC50 value of 75.7 mu g/mL. Furthermore, plant extracts with high antioxidant activities were not invariably efficient for disaggregating pre-formed A beta aggregates. Conclusion: High antioxidant activities were positively correlated with the inhibition of A beta aggregation, although not with the disaggregation of pre-formed A beta aggregates. Nevertheless, potent antioxidants may be helpful in treating Alzheimer's disease.