Selective in vitro antileishmanial activity of Mimosa caesalpiniifolia stem barks and its main constituent betulinic acid against Leishmania amazonensis

Abstract

IntroductionThe need of novel antileishmanial compounds with a wide therapeutic index has been a challenge for the pharmaceutical industry in reducing the side effects resulted from treatment with chemotherapeutics. The present study aims to investigate the antileishmanial and cytotoxic activities of the ethanol extract (EtOH), the dichloromethane fraction (DCM) and its isolated constituent betulinic acid (BA) obtained from the stem bark of Mimosa caesalpiniifolia Benth. (Fabaceae). MethodsThe antiproliferative effect on Leishmania amazonensis promastigotes was assessed by the Alamar Blue® colorimetric assay. The intramacrophagic amastigotes were exposed to different concentrations of EtOH, DCM and BA to determine the survival index. Selectivity indexes towards parasites were calculated for each treatment performed. The modulation of macrophage activation state was investigated by observing structural (phagocytic and lysosomal activities) and cellular (nitrite production) changes. Results and discussionThe EtOH, DCM and BA were effective against Leishmania amazonensis promastigote forms (IC50: 4.63 ± 0.69, 0.38 ± 0.42 and 29.63 ± 4.63 µg•mL−1, respectively). The same was observed for axenic amastigotes forms (IC50: 4.8 ± 1.27, 0.56 ± 0.39 and 14.2 ± 2.01 µg•mL−1), with selectivity index higher than 20 for DCM and BA. The macrophages infection and the number of intracellular amastigotes were reduced to 54.6%, 52.7% and 27.5%, respectively, after treatments. On the other hand, both DCM and BA were not able to promote macrophages activation, but only EtOH. Since DCM have shown highest potency as antileishmanial agent, BA presented a highest selectivity index. ConclusionThese results demonstrate the importance of M. caesalpiniifolia as a source of promising compounds since both DCM and BA might be investigated as promising and safe candidates for treatment of leishmaniasis. This work opens for further studies with M. caesalpiniifolia and betulinic acid focused on elucidation of possible involved mechanisms of antileishmanial action, as well as the potential in vivo treatment in experimental models of leishmaniasis.