Ethnobotany and Natural Products: The Search for New Molecules, New Treatments of Old Diseases or a Better Understanding of Indigenous Cultures?
Pp. 431-450 (20)
Results of various projects on Mexican Indian ethnobotany and some of the subsequent pharmacological and phytochemical studies are summarised focusing both on chemical-pharmacological as well as anthropological (ethnopharmacological) aspects of our research. We have identified taste and smell properties of medicinal (vs. non-medicinal) plants as important indigenous selection criteria. There exist well-defined criteria specific for each culture, which lead to the selection of a plant as a medicine. This field research has also formed a basis for studies on bioactive natural products from selected species. The bark of Guazuma ulmifolia showed antisecretory activity (cholera toxin-induced chloride secretion in rabbit distal colon in an USSING chamber). Active constituents are procyanidins with a polymerisation degree of eight or higher. Byrsonima crassifolia yielded proanthocyanidins with (+) epicatechin units and Baccharis conferta showed a dose-dependant antispasmodic effect with the effect being particularly strong in flavonoid-rich fractions. Our ethnopharmacological research led to the identification of sesquiterpene lactones (SLs) like parthenolide as potent and relatively specific inhibitors of the transcription factor NF-kB, an important mediator of the inflammatory process. The inhibitory effect of SLs is very strongly enhanced by the presence of such groups as the isoprenoid ring system, a lactone ring containing a conjugated exomethylene group (a-methylene-g-lactone) and an a,b-unsaturated cyclopentenone or a conjugated ester moieties. Our work also elucidated the NF-kB inhibiting activity of the photosensitiser phaeophorbide A from Solanum diflorum (Solanaceae) in PMA induced HeLa cells. Hyptis verticillata yielded a series of lignans as well as sideritoflavone, rosmarinic acid and (R)- 5-hydroxypyrrolidin-2-one and is rich in essential oil (rich in a-pinene, b- pinene and thymol). Other species investigated include Begonia heracleifolia, Crossopetalum gaumerii, Epaltes mexicana, Pluchea symphytifolia and Xanthosoma robustum.
Centre for Pharmacognosy and Phytotherapy, The School of Pharmacy, University of London, 29-39 Brunswick Square, London, WC1N 1AX, UK.