Chemometric approach for the discovery of biologically active compounds in Phytolacca americana roots

The diversity and variability exhibited in the metabolomes of natural materials makes discovery and identification of biologically active natural products from these materials a daunting endeavour. It is simply not possible to isolate, identify, characterize and determine the biological effects associated with every single natural product in every single natural material. Even within a single natural material sample, the exact levels and types of chemicals found within can change, being affected by a large variety of variables including, environmental conditions, harvesting conditions and preparation methods. As the biological effects of a sample is dependent on its chemical profile, any changes within these profiles can result in corresponding changes in its biological activities. It is proposed that an approach utilizing chemometric comparisons of active and non-active samples could be used to facilitate the discovery of bioactive natural products. The utility and potential of this approach was assessed through a study on Phytolacca americana L. (Phytolaccaceae), a plant with known toxic and anti-inflammatory activities. P. americana root samples harvested in different months were prepared into tinctures. Chemical profiles for the samples were obtained using UPLC-Q-TOF-MS. The samples were tested for inhibition of iNOS activity, activation of PPARα and PPARγ and cytotoxicity against RAW264.7 cells. Chemometric comparisons between samples showing different levels of bioactivity were performed. These comparisons showed correlation between triterpenoid saponins and the bioactivity exhibited by the samples. Among the compounds identified as being present at significantly higher levels in active samples versus non-active samples were three compounds biologically active compounds, namely phytolaccoside D, phytolaccagenin and phytolaccoside A. The results from this study provide evidence supporting the use of this chemometric approach for the discovery of biologically active natural products.

Acknowledgements: This research was supported in part by Science Based Authentication of Dietary Supplements funded by the Food and Drug Administration grant number 1U01FD004264 and USDA Agricultural Research Service Specific Cooperative Agreement #58 – 64081 – 603. Ms. Katherine Martin and John Trott are acknowledged for technical support in the bioassays and Dr. Aruna Weerasooriya and Dr. Lucile M. McCook are acknowledged for assistance in preparation of voucher specimens.

Keywords: Chemometrics, Phytolacca americana (Phytolaccaceae), UHPLC/Q-TOF-MS, PPAR, triterpenoid saponins.