Objective: Currently, red clover extract is used to treat menopausal disorders as an alternative to classic hormone therapy. Several human and animal studies have attributed hypolipidemic, hypoglycemic, or antiatherosclerotic effects to red clover extract or isoflavones. This study was designed to determine the peroxisome proliferator-activated receptor (PPAR) gamma activation by red clover extract.
Design: The PPARgamma binding affinities and the transactivation activities of red clover extracts, isoflavones, and their metabolites were analyzed. The presence of specific substances in the extracts was proved by high-performance liquid chromatography/electrospray ionization/mass spectrometry.
Results: The red clover extracts and the compounds genistein and biochanin A were potent PPARgamma ligands and activators. Several metabolites exerted higher binding affinities or transactivational activities than their precursor molecules. 6-Hydroxydaidzein exerted a more than 100-fold higher binding affinity than its precursor daidzein. The maximal transactivational activity of 6-hydroxydaidzein and 3'-hydroxygenistein exceeded even that of rosiglitazone, a known PPARgamma agonist. Equol and O-desmethylangolensin showed an approximately fivefold higher binding affinity and, in the case of O-desmethylangolensin, a fourfold higher PPARgamma agonistic activity than the precursor. The daily dose of Menoflavon forte, a widely used red clover extract for treatment of menopausal disorders, provides theoretically 15% to 30% of the daily recommended dose of rosiglitazone. Considering the more active metabolites formed, activity must be higher in vivo.
Conclusions: This study shows that red clover extracts, the major compounds, and especially several main metabolites exert significant PPARgamma binding and transactivational activity. Red clover extract, which is currently used for treating menopausal disorders, could be simultaneously used for ameliorating the metabolic syndrome.