Establishing compositional guidelines for flavonoids and saponins in Gynostemma pentaphyllum

Gynostemma pentaphyllum (Thunb.) Makino has been the focus of extensive research over the past decade and this interest and popularity has lead the Australian regulator, the Therapeutics Goods Administration (TGA), to call for compositional guidelines. There are no official monographs for this herb. Of particular interest in G. pentaphyllum is its demonstrated anti-obesity effects in animals and a human trial, possibly by its activation of AMP-activated protein kinase. Patented heat and steam processing of the natural extract has increased the levels of gypenosides L and L1 as well as the damulins A and B, the latter two causing, at least in vitro, a significant increase in AMP-activated protein kinase activity. Such a patent protected, refined extract would not be accepted as a natural extract and hence it is important to identify precursors in the natural extract to ensure quality in any subsequent processed product. These precursor saponins potentially include the gypenosides XLII, XLIII, XLVI and LVI and their subsequent conversion has been investigated here.

To address a compositional guideline, the compositions of both infusions and tinctures were assessed. The work undertaken and presented here encompasses total flavonoids and saponins as well as more detailed investigations by UPLC-MS of extracts for specific flavonoid and saponin composition. Plant materials surveyed include a range of commercially available Jiaogulan teas as well as various commercially available powdered extracts. Fresh plant material grown in northern New South Wales, Australia was used as a baseline reference herb for the research conducted here, although this has some limitations as there is phytochemical variation of this plant across its natural distribution through South East Asia.

Keywords: Gynostemma pentaphyllum, phytochemistry, UPLC-MS.