In vitro antiprotozoal and cytotoxic activity of 33 ethonopharmacologically selected medicinal plants from Democratic Republic of Congo

Abstract

Ethnopharmacological relevance

The antiprotozoal and cytotoxic activity of the aqueous extracts from 33 medicinal plants, used by traditional healers for the treatment of various parasitic diseases and collected after an ethnopharmacological inventory conducted in the Bolongo area, Bandundu province in DR Congo, was evaluated.

Materials and methods

Decoctions were prepared, lyophilized and evaluated for in vitro antiprotozoal activity against Trypanosoma b. brucei, Trypanosoma cruzi, Leishmania infantum, and the chloroquine- and pyrimethamine-resistant K1 strain of Plasmodium falciparum. Cytotoxicity against MRC-5 cells was included to assess selectivity of activity.

Results

Most of the tested extracts exhibited pronounced (IC₅₀ ≤ 5 μg/ml) or good (5 < IC₅₀ ≤ 10 μg/ml) antiprotozoal activity against one or more of the selected protozoa. A total of 19 plant extracts inhibited Trypanosoma b. brucei, especially the extract from Isolona hexaloba stem bark (IC₅₀ = 1.95 μg/ml, SI = 16.5); 8 plant extracts were active against Trypanosoma cruzi, the extracts from Enanatia chlorantha stem bark and Quassia africana root bark being the most active with IC₅₀ values of 1.87 and 1.88 μg/ml, respectively (SI = 3.0 and 3.3, respectively); 8 plant extracts showed activity against Leishmania infantum, with extracts from Napoleona vogelii stem bark and Quassia africana root bark as the most active with IC₅₀ values of 5.66 and 5.04 μg/ml (SI = 11.3 and 1.2). Finally, 9 plant extracts inhibited Plasmodium falciparum K1 with the extracts from Quassia africana (root bark and stem bark) being the most active ones with IC₅₀ values of 0.46 and 1.27 μg/ml (SI = 13.7 and 13.6). Extracts from Enantia chlorantha stem bark, Piptadeniastrum africanum stem bark and Quassia africana root bark were cytotoxic for MRC-5 cells (CC₅₀ < 10 μg/ml).

Conclusions

These results can partly support and justify the traditional use of some of these plant species for the treatment of parasitic diseases.

Introduction

Protozoa are responsible for various infections that occur primarily with high endemicity in many developing countries. They remain a major public health concern in tropical and subtropical regions in view of their immense social impact on individuals, families and affected communities (Nantulya, 1997, Kyambadde et al., 2000).

In Sub-Saharan Africa, several Trypanosoma species cause important veterinary diseases, but only two cause significant suffering in man: Trypanosoma b. gambiense and Trypanosoma b. rhodesiense, respectively, causing chronic and acute sleeping sickness or human African trypanosomiasis (HAT). The disease occurs in 36 sub-Saharan African countries and in the last 10 years, over 70% of reported cases occurred in the Democratic Republic of Congo (DR Congo). HAT may results in a 100% mortality rate if left untreated (Gracia et al., 2006, WHO, 2010a, Hannaert, 2011). In South America, Trypanosoma cruzi causes Chagas disease. It is estimated that 11–18 million people are infected and 100,000 people are at risk of acquiring it (Barrett et al., 2003). Leishmaniasis is regarded as a major public health problem, causing significant morbidity and mortality in Africa, Asia and Latin America (WHO, 2002). The disease currently threatens about 350 million people in 88 countries around the world, with about 2 million affected annually (Ashford, 2000, Carvalho et al., 2000). Despite all efforts made to eradicate malaria, the mortality and morbidity still increase each year mainly because of drug resistance of Plasmodium falciparum. WHO estimates that with 300–500 million clinical cases and more than 2 million deaths each year, malaria remains one of the three most deadly communicable diseases in the world (Wellems and Plowe, 2000, Winstanley, 2000, WHO, 2010b).

In endemic countries, medicinal plants have traditionally been used for centuries to treat parasitic conditions, and people found some relief without scientific data that could justify and support their use. Nowadays, investigations are carried out on extracts from various medicinal plants to investigate their efficacy against different protozoa. In previous studies, some of them have been reported to possess promising antiprotozoal potential (Hoet et al., 2004, Mesia et al., 2008, Maregesi et al., 2010, Xu et al., 2011). In the frame of the projet “Cuvette Centrale as reservoir of medicinal plants in DRCongo” (Fruth, 2011), an ethnopharmacological inventory was conducted in the Bolongo-area, Mai-Ndombe district, Bandundu province. By focusing on plants traditionally used for the treatment of various parasitic diseases as claimed by traditional healers who were interviewed (Mato, 2005, Musuyu Muganza, 2006, Fruth et al., 2011), 33 plant species were selected and collected. From a literature search, it appeared that many of these had never been evaluated for their antiprotozoal and cytotoxic potential. Hence, the present study focused on the in vitro evaluation of the antiprotozoal activity of lyophilized extracts of the decoctions from these medicinal plants against Trypanosoma b. brucei, Trypanosoma cruzi, Leishmania infantum and Plasmodium falciparum. Their cytotoxic effects against MRC-5 cells were assessed as well.