Identification and development of active principles from plant sources

Plants are the source of wide variety of molecules with potential therapeutic application. More than 80 percent of the world population still relies on traditional medicine systems, which are mostly based on herbal remedies. Furthermore, about 35 percent of the currently available medicines have been developed using natural products as a lead compound. One of the major limitations for the clinical use of natural products, both as isolated compounds and as complex herbal extracts, is represented by the limited knowledge of their pharmacokinetic properties. Indeed, several experimental models, including in vivo, cell-free and cell-based, together with in silico methods have been developed for the evaluation of pharmacokinetic parameters, such as gastrointestinal stability, intestinal absorption, and hepatic metabolism. However, these methods are barely applied to natural products, particularly to herbal extracts. The main difficulty in the study of pharmacokinetic parameters of herbal products originates from their complex nature: a herbal product, in fact, is composed of hundreds of molecules. As a consequence, the choice of a marker compound for pharmacokinetic studies is crucial but sometimes difficult. Moreover, the mixture of constituents in an herbal extract could potentially modulate the biological properties of single natural products. On this basis, extrapolation of pharmacokinetic parameters of herbal extracts by only relying on data acquired for single compounds could be a challenging issue. Obtaining pharmacokinetic data on different natural products and herbal extracts is, hence, an urgent task. Particularly, ability to predict at least several of these parameters by using fast and cost-effective computational tools will be of great benefit to the pharmaceutical and food supplement research and industry. In this study, we used a simple cell-free method to evaluate the effect of in vitro simulated gastrointestinal digestion on the stability, bioaccessibility, and biological effects of several natural products, belonging to different classes of polyphenols, and herbal extracts containing them. We also used the Caco-2 cell permeability assay to evaluate the intestinal absorption of mixtures of compounds administered at the same time. In most cases, we found that administration of herbal extracts protect its constituents from degradation induced by the digestive processes, while intestinal bioavailability is often reduced when using mixtures of compounds. Moreover, an in silico virtual screening protocol based on molecular docking and pharmacophore modeling was used to identify new putative P-glycoprotein ligands from natural sources. The computational tool was first checked for its ability to discern between known P-gp binders and non-binders, and then used to prioritize compounds from commercial sources of natural compounds. Assays on selected compounds will provide full validation of the virtual screening approach. The overall aim of this work is to enlarge the knowledge on pharmacokinetic parameters of natural products and herbal extracts to be used for setting up a computational model able to predict the pharmacokinetics parameters of complex mixtures of compounds.