Evaluation of total phenolic fraction derived from extra virgin olive oil for its antileishmanial activity

Leishmaniasis is a neglected and emerging disease with varying clinical manifestations. The current treatment options rely on limited chemotherapy with serious drawbacks. Thus, there is an increasing interest in the identification of new candidates for designing potent, less toxic and low-cost drugs.

The purpose of this study was to evaluate the potential antileishmanial activity of the total phenolic fraction (TPF) derived from extra virgin olive oil (EVOO) when added in in vitro and in vivo experimental models of Leishmania infection.

We investigated the in vitro antileishmanial activity of TPF against two Leishmania species: a viscerotropic (L. infantum) and a dermotropic (L. major) strain. The antileishmanial effect was also tested in vivo in a murine cutaneous leishmaniasis model using L. major-infected BALB/c mice.

Separation and analytical methodologies were applied in order to extract the olive oil phenols (TPF) and determine the concentration of the major ones, respectively. The in vitro antileishmanial activity of TPF against promastigotes and intracellular amastigotes was determined by the resazurin cell viability assay. The TPF-induced nitric oxide synthesis by L. infantum and L. major -infected J774A.1 macrophages was determined using the Griess reaction, while the respective generation of reactive oxygen species was assessed by flow cytometry. Moreover, L. major-infected BALB/c mice were treated with TPF and its in vivo therapeutic effect was determined as reduction of the footpad swelling.

Our data showed that TPF exhibits inhibitory effect against cell free promastigotes and intracellular amastigotes of both L. infantum and L. major parasite strains. TPF demonstrated to be selectively active against Leishmania amastigotes and its antileishmanial activity was possibly mediated by reactive nitrogen and oxygen intermediates generated from the infected J774A.1 macrophages. Furthermore, administration of TPF in BALB/c mice infected with L. major caused significant reduction of footpad swelling demonstrating in vivo its antileishmanial effect. Based on HPLC-DAD analysis the major components of TPF are tyrosol, hydroxytyrosol, oleacein and oleocanthal.

This study brings a new low-cost candidate to the leishmaniasis drug discovery pipeline, upon further pharmacological investigation.