In Angola, Human African Trypanosomiasis is caused by the protozoal subspecies Trypanosoma brucei gambiense and is transmitted by tsetse flies (Glossina spp.). It is endemic in seven provinces of the country, and an estimated 5.8 million people are at risk. Despite availability of an effective standard treatment and control activities, a certain number of cases are undetected and untreated, these are mainly found among hard-to reach communities, much exposed to the disease with difficult access to healthcare. In such context, the investigation of herbal remedies as a natural affordable and accessible resource is of high relevance. There is a lack of information on Angolan medicinal plants currently used against trypanosomiasis. In the presented PhD study, I have investigated the actual use of traditional herbal remedies in the management of this disease. By investigation of the access to and the use of the traditional remedies, I aimed to fill up this gap by delivering useful information regarding the usage of the medicinal plants and the antitrypanosomal potential of the reported traditional recipes.
First, I implemented and conducted an exploratory study in four northern endemic provinces of Angola. The ethnomedical and ethnobotanical analysis revealed that among the infected persons, 40% turn to folk medicine before consulting a medical doctor. Moreover, 30 plant species were mentioned in the management of the disease, of which Crossopteryx febrifuga was the most cited plant. In addition, the study highlighted the use of plants with potential toxicity risk, as for example an herbal preparation containing the roots of Aristolochia gigantea.
I further selected 9 species (of 30) for in vitro antitrypanosomal screening, according to four selection criteria: (1) the Use Report, (2) the correlation between traditional reported preparation and clinical data, (3) the quality of the narrative content, and (4) the novelty of the plant.
I pursued with the bioguided-activity screening of the 9 plant species, out of which 122 plant extracts were produced. Two crude extracts, the 80% ethanolic extract of Brasenia schreberi (leave) and the dichloromethane extract of Nymphaea lotus (leaf and petiole) displayed IC50 values < 10 µg/ml against Trypanosoma brucei rhodesiense, and were retained for bioguided-fractionation and isolation of active constituents. 7 active phenols for B. schreberi , namely gallic acid (1), methyl gallate (2), tetragalloylglucose (3), ethyl gallate (4), 1,2,3,4,6 pentagallyl-β-glucopyranoside (5), gossypetin-7-O-β-glucopyranoside (6), hypolaetin-7-O-glucoside (7), and 1 active compound for N. lotus, a resorcinol alkyl (8). Compounds (2-3, 5-6) were reported for the first time in the genus Brasenia and the presence of compound (8) was so far not described in the Nymphaeacea. The antitrypanosomal potential of the traditional preparation made of these two aquatic plants was assessed. We could evidence the presence of 3 active constituents in both decoctions: gallic acid, methyl gallate, and 1,2,3,4,6-Pentylgalloyl-β-glucopyranoside.
Taken together, this work provided primary evidence for the rational use of a traditionally used preparation made of Brasenia schreberi and Nymphaea lotus. As so, these results contributed to the scientific validation of an herbal remedy used in the management of sleeping sickness in Angola
