Isolation, purification, and characterization of immunosuppressive compounds from tripterygium: triptolide and tripdiolide.

Crude extracts derived from the root of Tripterygium wilfordii Hook f (TWHf) have previously been demonstrated to have immunosuppressive properties and have been used as anti-rheumatic therapy in Chinese traditional medicine. Although these extracts contain a large number of chemical components, the precise nature of the compound(s) responsible for this therapeutic effect has not been established with certainty. An aqueous extract of TWHf was resolved into chemical components by medium-pressure and high-performance liquid chromatography. Immunosuppressive fractions were identified with a mixed lymphocyte reaction (MLR) and chemically characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Two major peaks of immunosuppressive activity were identified. These were the closely related diterpenoid triepoxides, triptolide and tripdiolide. No other immunosuppressive compounds were identified using MLR as the biologic screening assay. Triptolide and tripdiolide may be responsible for the anti-rheumatic properties of crude aqueous extracts of TWHf and represent a novel class of immunosuppressive drugs with potential clinical utility.