In vitro and in vivo anti-leishmanial activity of triterpenoid saponins isolated from Maesa balansae and some chemical derivatives.

The methanolic extract from the leaves of the Vietnamese medicinal plant Maesa balansae showed potent in vitro and in vivo activity against the tropical protozoal parasite Leishmania infantum. Bioassay-guided purification of the extract led to the identification of six triterpenoid saponins, maesabalides I-VI (1-6), each having a strong and specific anti-leishmanial activity. Maesabalide III (3) and IV (4) were the most potent with IC(50) values against intracellular amastigotes of about 7 and 14 ng/mL. In comparison, the IC(50) value of sodium stibogluconate, the reference drug for treatment of leishmaniasis, is only 5.6 microg/mL. No cytotoxicity was present on a human fibroblast (MRC-5) cell line (CC(50) > 32 microg/mL). In vivo evaluation in the BALB/C mouse model demonstrated that >90% reduction of liver amastigote burdens was obtained 1 week after a single subcutaneous dose at 0.2-0.4 mg/kg was administered. Several chemical derivatives of maesabalides I-VI were prepared in order to study the structure-activity relationship.

Liquid chromatographic method for analysis of saponins in Maesa balansae extract active against leishmaniasis.

A liquid chromatographic method was developed for the separation of six related triterpenoid saponins in Maesa balansae extracts with different purity, active against leishmaniasis. As stationary phase a Hypersil BDS C18 column (3 microm), 100 x 4.6 mm was used. The mobile phase was a mixture of methanol, acetonitrile, 5% (m/v) ammonium acetate, pH 6.5 and water. A linear gradient was developed for the analysis of crude extracts. An isocratic method was developed to analyze purified samples that mainly contained saponins 3 and 4, the most active saponins. The isocratic LC method was optimized and the robustness was evaluated with an experimental design. The method showed good selectivity, repeatability, linearity and sensitivity.

Comparative activities of the triterpene saponin maesabalide III and liposomal amphotericin B (AmBisome) against Leishmania donovani in hamsters.

Maesabalide III (MB-III), an oleane triterpene saponin isolated from the Vietnamese plant Maesa balansae, is a new antileishmanial lead compound whose activity against Leishmania donovani (MHOM/ET/67/L82) in groups of five golden hamsters was evaluated after administration of a single subcutaneous dose on either day 1 (prophylactic treatment) or day 28 (curative treatment) after infection. Liposomal amphotericin B (AmBisome), administered intravenously at 5 mg/kg of body weight, was used as the reference drug. Amastigote burdens in liver, spleen, and bone marrow were determined either 7 days (early effects) or 56 days (late effects) after treatment. Prophylactic administration of MB-III at 0.2 mg/kg reduced liver amastigote burdens by 99.8 and 83% within 7 and 56 days after treatment, respectively. In the latter group, however, all animals became ill and some died. Both MB-III at 0.8 mg/kg and liposomal amphotericin B were 100% effective against liver stages, but clearance from the spleen and bone marrow was not achieved. Curative administration of MB-III at 0.2 and 0.4 mg/kg was not protective, as no survivors were left at the termination of the experiment on day 84. Despite the high level of reduction of the liver amastigote burden after treatment with MB-III at 0.8 mg/kg (94.2%) or liposomal amphotericin B (99.4%), clinical protection could not be obtained in either group, with two deaths occurring and the residual liver burdens persisting. It is concluded that administration of a single dose of MB-III at 0.8 mg/kg has efficacy potential comparable to that of a single dose of liposomal amphotericin B at 5 mg/kg and is therefore considered a promising new antileishmanial lead compound. However, multiple-dose pharmacological, toxicological, and pharmacokinetic studies are still needed before it can become a valid drug candidate for development.

In vitro and in vivo activities of a triterpenoid saponin extract (PX-6518) from the plant Maesa balansae against visceral leishmania species.

The in vitro and in vivo activities of a mixture of six oleane triterpene saponins, recovered from the methanolic extract of the leaves of the Vietnamese plant Maesa balansae (PX-6518), were evaluated against drug-sensitive visceral Leishmania strains. The in vitro 50% inhibitory concentration (IC(50)) against intracellular Leishmania infantum amastigotes was 0.04 micro g/ml. The cytotoxic concentrations causing 50% cell death (CC(50)s) were about 1 micro g/ml in murine macrophage host cells and >32 micro g/ml in human fibroblasts (MRC-5 cell line). Evaluation in the Leishmania donovani BALB/c mouse model indicated that a single subcutaneous administration of 0.4 mg/kg at 1 day after infection reduced liver amastigote burdens by about 95% in all treated animals. If treatment was delayed until 14 days after infection, a dose of 1.6 mg/kg of body weight was required to maintain the same level of activity. Single 250-mg/kg doses of sodium stibogluconate (Pentostam) 1 and 14 days after infection produced comparable efficacies. A single dose of PX-6518 at 2.5 mg/kg administered 5 days before infection was still 100% effective in preventing liver infection, suggesting a particularly long residual action. Spleen and bone marrow could not be cleared by PX-6518 nor sodium stibogluconate. PX-6518 did not show activity after oral dosing at up to 200 mg/kg for 5 days. This study concludes that triterpenoid saponins from M. balansae show promising in vitro and in vivo antileishmanial potential and can be considered as new lead structures in the search for novel antileishmanial drugs.