Unbiased evaluation of bioactive secondary metabolites in complex matrices

Abstract

The majority of bioactive principles in a complex matrix such as natural products and botanical medicines are secondary rather than primary metabolites. In addition to being chemically diverse, the bioactivity of an ethnobotanical can comprise from one to several bioactive compounds, present in a complex mixture. Conventional discovery efforts utilize bioassay-guided fractionation (BGF) to isolate individual active compounds. When applied to complex natural products, BGF is often challenged by an apparent loss of activity during fractionation, resulting in weakly active isolated compounds. Metabolomic analysis can potentially complement existing the BGF paradigm by capturing the chemical complexity of the metabolites. The proposed biochemometric approach establishes a link between the chemistry of a secondary metabolome and a deserved health impact, using a high-throughput, high-resolution capable biological endpoint. The proof of principle is demonstrated for the anti-tuberculosis (TB) activity of the Alaskan ethnobotanical, Oplopanax horridus. Biochemometric analysis identified the 100 most active constituents from thousands of metabolites in the active extract by means of 2D orthogonal chromatography using countercurrent and GC-MS methods. Previously isolated O. horridus phytoconstituents were used as reference markers of known structure and bio (in)activity. Positive correlations allowed distinction of anti-TB actives from inactive compounds. A total of 29 bioactives from 3 main structural classes were assigned based on MS data. Biochemometric analysis is a new tool for the standardization of herbal medicines and ethnobotanicals, as well as for drug discovery from nature. The method can assign multiple active compounds in complex mixtures without their prior isolation or structure elucidation, while still providing an interface to structural information.