Limonene-carvacrol: A combination of monoterpenes with enhanced antileishmanial activity

Leishmaniasis is a parasitosis with a wide incidence in developing countries. The drugs which are indicated for the treatment of this infection usually are able to promote high toxicity.

A combination of limonene and carvacrol, monoterpenes present in plants with antiparasitic activity may constitute an alternative for the treatment of these diseases.

In this study, the antileishmania activity against Leishmania major, cytotoxicity tests, assessment of synergism, parasite membrane damage tests as well as molecular docking and immunomodulatory activity of limonene-carvacrol (Lim-Car) combination were evaluated.

The Lim-Car combination (5:0; 1:1; 1:4; 2:3; 3:2; 4:1 and 0:5) showed potential antileishmania activity, with mean inhibitory concentration (IC₅₀) ranging from 5.8 to 19.0 μg.mL^-1. They demonstrated mean cytotoxic concentration (CC₅₀) ranging from 94.1 to 176.0 μg.mL^-1, and did not show significant hemolytic effect. In the investigation of synergistic interaction, the 4:1 Lim-Car combination showed better fractional inhibitory concentration (FIC) index as well as better activity on amastigotes and IS. The samples caused considerable damage to the parasite membrane this monoterpene activity seems to be more related to Trypanothione Reductase (TryR) enzyme interaction, demonstrated in the molecular docking assay. In addition, the 4:1 Lim-Car combination stimulated macrophage activation, and showed at was the best association, with reduction of infection and infectivity of parasitized macrophages.

The 4:1 Lim-Car combination appears to be a promising candidate as a monotherapeutic antileishmania agent.