Inhibitory Activity on Amyloid Aggregation of Rosmarinic Acid and Its Substructures From Isodon japonicus

Nowadays, the incidence of Alzheimer's disease (AD) and type 2 diabetes (T2D) is increasing at an alarming rate. More and more studies have been investigating the relationship between these two diseases and are trying to find an effective treatment. According to amyloid hypothesis, it is very necessary to find phenolic compounds with catechol moieties, which would inhibit the aggregation of amyloid (A) and human islet amyloid polypeptide (hIAPP), while also exhibiting antioxidant activity and protective effect. We isolated rosmarinic acid (RA) from the plant Isodon japonicus (Burm.f.) H. Hara. Thioflavin T assay and transmission electron microscopy observation were carried out to evaluate the inhibitory effect of RA, caffeic acid, and 3,4-dihydroxyphenyllactic acid, which are the substructures of RA, on both A and hIAPP fibrillization. 2,2-Diphenyl-1-picrylhydrazyl assay was applied to test the antioxidant activity. RA showed inhibitory effect on both peptides and strong antioxidant activity. These results suggest that the existence of catechol units plays an important role on the inhibitory activity. Therefore, RA will be a promising strategy to prevent AD and T2D.