Title : Assessment of Marquesan Rauvolfia nukuhivensis bioactive content
Rauvolfia genus, grown in tropical areas, is well-known for its many species used in traditional medicine which healing properties inspired pharmacological studies leading to successful discovery of innovative drugs through years. Finding of these drugs were directly related to ethnopharmacological uses of these Rauvolfia species and regarding endangered species ones, it became very urgent to conduct phytochemical study the bioactive alkaloidal plant content not only before biodiversity loss but also before traditional knowledge erosion aiming for plant and human heritage conservation program and actions. Rauvolfia nukuhivensis, called locally “tueiao”, is an endemic species grown in Nuku-Hiva island located in Marquesas archipelago in French Polynesia where the bark is used for intimate woman care. Ethnopharmacological approach was adopted to assess this plant content. For that purpose, firstly, antimicrobial effects was checked if the plant extract played an antiseptic role by testing the extract and contents on bacterial and fungi strains (Escherichia coli, Staphylococcus aureus, Candida albicans and Aspergillus niger) and bioassay results showed moderate to low activities. Then, traditional medicinal information regarding this plant led to establish hypothesis that its uses may be linked to biological activities having close relationship with secretory mechanisms regulation. Thus, this second hypothesis was explored by investigation of ion channels inhibition related to osmotic exchanges and then, inhibiting effects on hNav1.6 currents and hERG channel were so tested. Some alkaloidal constituents, and more especially nukuhivensiums, were shown to significantly induce a reduction of IKr amplitude (hERG current). According to these biological activity results, a computational study through docking was performed in order to design the bioactive pharmacophore of the alkaloidal plant constituents. The alkaloidal composition of the bark of this plant was assessed by integrated approaches mainly: structural elucidation, phylogenetic analysis and a putative biosynthesis hypothesis statement. Structural elucidation by spectroscopic means (MS, NMR) led to the identification of 13 major constituents belonging to four distinct indole alkaloid skeletons (ajmalane, sarpagane, macroline and ?-carboline). As the Rauvolfia genus is well distributed in the Pacific region, a phylogenetic study was carried out (using DNA barcoding method) of Rauvolfia species, endemic or indigenous in Oceania, as a second approach, aiming to a better understanding of the occurence and distribution of these alkaloids. The very rare co-occurence of these alkaloids belonging to four different skeletons inspired to set up a putative biosynthesis of these components. These data will be helpful to further conservation plans of this endangered species.