The antiprotozoal activity of methylated flavonoids from Ageratum conyzoides L.

Aim of the studyThe dichloromethane extract prepared from aerial parts of Ageratum conyzoides L. (Asteraceae), a plant commonly used in folk medicine for a number of illnesses including sleeping sickness, was recently found to exhibit a prominent activity (IC50 = 0.78 μg/mL) against bloodstream forms of Trypanosoma brucei rhodesiense, the etiologic agent of East African Human Trypanosomiasis (East African Sleeping Sickness). This extract also exhibited noticeable activities against Leishmania donovani (Kala-Azar, IC50 = 3.4 μg/mL) as well as Plasmodium falciparum (Malaria tropica, IC50 = 8.0 μg/mL). In the current study, we sought for potentially active constituents of Ageratum conyzoides.Materials and methodsExtracts prepared with solvents of different polarity were tested for activity against the above mentioned parasites as well as against Trypanosoma cruzi (Chagas’ disease) and for cytotoxicity using established protocols. The dicholoromethane extract showed the highest level of activity and was chosen for phytochemical studies aimed at the isolation of potential active constituents.Results and conclusionFive highly methoxylated flavonoids along with the chromene derivative encecalol methyl ether were isolated. All isolated compounds were previously reported from Ageratum conyzoides. While the chromene turned out to be inactive against the tested parasites, the flavonoids showed activity against the protozoan pathogens, some in the lower micromolar range. However, none of these isolated compounds was as active as the crude extract. This is the first report on antiprotozoal activity of this plant species and some of its constituents. The chemical principle accounting for the high activity of the crude extract, however, remains to be identified.

Graphical abstractThe crude dichloromethane extract of the aerial parts of Ageratum conyzoides L. (Asteraceae) showed high in vitro activity against several protozoan parasites (Trypanosoma, Leishmania, Plasmodium) in vitro. Five methoxylated flavonoids and a chromene derivative were isolated and tested. While the chromene was inactive, the flavonoids showed moderate antiprotozoal activity but were not fully accountable for the inherent bioactivity observed in the original crude extract.Figure optionsDownload full-size imageDownload as PowerPoint slide