Reverse pharmacology for developing an anti-malarial phytomedicine. The example of Argemone mexicana.

Classical pharmacology has been the basis for the discovery of new chemical entities with therapeutic effects for decades. In natural product research, compounds are generally tested in vivo only after full in vitro characterization. However drug screening using this methodology is expensive, time-consuming and very often inefficient. Reverse pharmacology, also called bedside-to-bench, is a research approach based on the traditional knowledge and relates to reversing the classical laboratory to clinic pathway to a clinic to laboratory practice. It is a trans-disciplinary approach focused on traditional knowledge, experimental observations and clinical experiences. This paper is an overview of the reverse pharmacology approach applied to the decoction of Argemone mexicana, used as an antimalarial traditional medicine in Mali. A. mexicana appeared as the most effective traditional medicine for the treatment of uncomplicated falciparum malaria in Mali, and the clinical efficacy of the decoction was comparable to artesunate-amodiaquine as previously published. Four stages of the reverse pharmacology process will be described here with a special emphasis on the results for stage 4. Briefly, allocryptopine, protopine and berberine were isolated through bioguided fractionation, and had their identity confirmed by spectroscopic analysis. The three alkaloids showed antiparasitic activity in vitro, of which allocryptopine and protopine were selective towards Plasmodium falciparum. Furthermore, the amount of the three active alkaloids in the decoction was determined by quantitative NMR, and preliminary in vivo assays were conducted. On the basis of these results, the reverse pharmacology approach is discussed and further pharmacokinetic studies appear to be necessary in order to determine whether these alkaloids can be considered as phytochemical markers for quality control and standardization of an improved traditional medicine made with this plant.

Chemical composition of the bark of Tetrapterys mucronata and identification of acetylcholinesterase inhibitory constituents.

The secondary metabolite content of Tetrapterys mucronata, a poorly studied plant that is used occasionally in Brazil for the preparation of a psychotropic plant decoction called "Ayahuasca", was determined to establish its chemical composition and to search for acetylcholinesterase (AChE) inhibitors. The ethanolic extract of the bark of T. mucronata exhibited in vitro AChE inhibition in a TLC bioautography assay. To localize the active compounds, biological profiling for AChE inhibition was performed using at-line HPLC-microfractionation in 96-well plates and subsequent AChE inhibition bioautography. The analytical HPLC-PDA conditions were transferred geometrically to a preparative medium-pressure liquid chromatography column using chromatographic calculations for the efficient isolation of the active compounds at the milligram scale. Twenty-two compounds were isolated, of which six are new natural products. The structures of the new compounds (9, 10, 16-18, and 20) were elucidated by spectroscopic data interpretation. Compounds 1, 5, 6, 9, and 10 inhibited AChE with IC50 values below 15 µM.