B-ring-homo-tonghaosu, isolated from Chrysanthemum morifolium capitulum, acts as a peroxisome proliferator-activated receptor-γ agonist

The capitula of Chrysanthemum morifolium and C. indicum are used to prepare Chrysanthemi Flos in traditional Japanese Kampo medicine. In our previous study, we reported on the agonistic effect of methanol extract of C. indicum capitulum on peroxisome proliferator-activated receptor (PPAR)-γ. We further isolated (E)-tonghaosu from C. indicum capitulum as one of the active ingredients. In the present study, we aimed to evaluate the PPAR-γ agonistic activity of a methanol extract of C. morifolium capitulum (MCM) in which (E)-tonghaosu could not be detected. MCM exhibited PPAR-γ agonistic activity in a concentration-dependent manner, and at a dose of 100 µg/ml, it showed similar activity to pioglitazone (30 µM), a standard PPAR-γ agonist. Through activity-guided fractionation, we isolated two geometric isomers, (E)- (1) and (Z)-B-ring-homo-tonghaosu (2), as the active ingredients of MCM. Both compounds exerted concentration-dependent PPAR-γ agonistic effects, and 1 had higher activity than 2. At 1.4 µM, 1 had similar activity to pioglitazone (30 µM), which was achieved by 2 at a concentration of 140 µM. Thus, 1 has the potential to become a lead compound for the drug discovery of PPAR-γ agonists. We compared the activities and the contents of (E)-, (Z)-tonghaosu, 1, and 2 among 13 commercial samples of Chrysanthemi Flos, including those derived from both C. morifolium and C. indicum. Their PPAR-γ agonistic activities were not related to the contents of these compounds. 1 and 2 were detected in the samples derived from both species but (E)- and (Z)-tonghaosu were not detected in the samples derived from C. morifolium; hence (E)- and (Z)-tonghaosu can serve as marker compounds to identify the capitula of C. indicum in Chrysanthemi Flos samples.