Abstract

Objective: To investigate the antiprotozoal activity of medicinal plant extracts and isolated active compounds from the most active plant. Methods: Twenty one medicinal plants with ethnobotanical use in Thailand, which were claimed to have anti-diarrhoeal or anti-parasitic activity, were screened for their anti-intestinal protozoan activity against Entamoeba histolytica (E. histolytica) and Giardia intestinalis (G. intestinalis). The most active compound was isolated and tested against E. histolytica and G. intestinalis. Results: An acetone extract of Coptosapelta flavescens was the most active against both E. histolytica and G. intestinalis (minimal inhibitory concentration=1 25 and 1 5.63 μg/mL, respectively). Two anthraquinones and one naphthoquinone were isolated. The compound 1-hydroxy-2-hydroxymethylanthraquinone was the most active chemical against E. histolytica and G. intestinalis with minimal inhibitory concentration values of 20 and 2.5 μg/mL, respectively. In time killing assay, the percentage of viable G. intestinalis, when compare to control, after expose to compound 1-hydroxy-2-hydroxymethylanthraquinone showed significantly (P<0.05) lower than when exposed to a standard drug, metronidazole, at 6 and 12 h of incubation time. While for E. histolytica, its a=ctivity was comparable to metronidazole. Conclusions: These observations provide preliminary evidence that 1 -hydroxy-2- hydroxymethylanthraquinone from Coptosapelta flavescens can be considered to be a potential anti-parasitic agent against E. histolytica and G. intestinalis infections.

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