Inhibitory activity on amyloid-β aggregation and antioxidant properties of Crocus sativus stigmas extract and its crocin constituents

Crocus sativus stigmas are one of the widely known spices ( saffron) and consist of unusually polar carotenoids. Alzheimer's disease is characterized pathologically by deposition of amyloid beta-peptide (A beta) fibrils. Oxidation is thought to promote A beta fibril formation and deposition. To identify agents inhibiting the pathogenesis of Alzheimer's disease, we examined in vitro the antioxidant properties of extract of C. sativus stigmas and its effect on A beta(1-40) fibrillogenesis. The antioxidant properties were determined by measuring the ferric-reducing antioxidant power and Trolox-equivalent antioxidant capacity, while its effects on A beta-aggregation and fibrillogenesis were studied by thioflavine T-based fluorescence assay and by DNA binding shift assay. The water: methanol ( 50: 50, v/v) extract of C. sativus stigmas possesses good antioxidant properties, higher than those of tomatoes and carrots, and inhibited A beta fibrillogenesis in a concentration and time-dependent manner. The main carotenoid constituent, trans-crocin-4, the digentibiosyl ester of crocetin, inhibited A beta fibrillogenesis at lower concentrations than dimethylcrocetin, revealing that the action of the carotenoid is enhanced by the presence of the sugars. Our findings suggest the possible use of C. sativus stigma constituents for inhibition of aggregation and deposition of A beta in the human brain.