In Vitro Antileishmanial Activity of Bombax Ceiba Linn. Flowers

Abstract

Visceral leishmaniasis (VL) is one of the neglected tropical diseases, as many as 8 million people in the 13 endemic districts of Nepal. Incidence of VL is associated with poverty and is further pushing the poor to the poorest. Available treatment options are limited and unsatisfactory due to several limitations like parenteral administration, long course of treatment, toxic side effects and high treatment cost. Malnutrition and co-infection with diseases such as malaria, pneumonia, HIV and development of drug-resistance by parasites are further worsening the situation. In absence of a vaccine there is an urgent need of alternative treatments. One of the main sources for new antileishmanial agents are secondary metabolites isolated from plants. Nepal is rich in natural products biodiversity and habitats more than 900 types of valuable medicinal plants among 7000 medicinal plants found all over the world. However, these natural resource has largely been unexplored for its medicinal and therapeutic potential against leishmaniasis. Flowers of Bombax ceiba has been known for its several enthnomedicinal uses in various afflictions including splenomegaly, a hallmark of VL. To evaluate its potential use in VL an in vitro antileishmanial activity of the flowers of the plant was carried out. The crude ethanolic extract of the flower inhibited promastigote growth at IC 50 of 131.24 ± 12.54 µg/mL. The methanol fraction showed a greater inhibitory effect against promastigotes (IC 50 of 89.62 ± 0.55 µg/mL) and amastogotes (IC 50 of 58.73 ± 1.89 µg/mL) than the other fractions. Fraction n-hexane, also had appreciable inhibitory activity against promastigotes (105.12 ± 7.99 µg/mL) and amastigotes (61.39 ± 1.34 µg/mL), indicating the active compounds might have been attributed to these fractions. The reference drug miltefosine had lower 50% inhibitory concentration values for both forms of the parasite (IC 50 for promastigote: 11.27 ± 0.52 µg/mL and IC 50 for amastiogote: 4.12 ± 0.13 µg/mL) than any of the fractions or the crude extract. From the dose response curves and time dependent efficacy response graphs it can be conferred that n-hexane and methanol fractions are leishmanicidal and acetone and chloroform fractions are leishmanistatic. Also, hexane fraction was effective at low dose against promastigotes (IC 100 at 250 µg/mL) and so was methanol fraction against amastigotes (IC 100 at 125 µg/mL). Cytotoxicity test revealed the components were safe, with selectivity indices values greater than 1. Moreover, methanol fraction of the crude flower extract was found similar in activity of miltefosine when compared to at its CC50 concentration (P=0.0638). Identification of the effective compounds from methanol and n-hexane fractions could lead to discovery of lead compounds effective against kala-azar. To the best of our knowledge this is the first report to demonstrate antileishmanial activity of B. ceiba Linn. flowers. This work also focuses on the need of screening of medicinal plants native to Nepal for anti-leishmanial activity. Key words: Visceral leishmaniasis, Leishmania donovani, Bombax ceiba, Semal, IC50, In vitro, antileishmanial acitivity.