In Vitro Anti-Leishmanial Activity and Molecular Docking of Eugenol as a Potential Agent Against Leishmania Major

Eugenol is an aromatic compound that belongs to the phenol group found in various natural sources, such as clove oil. This study aimed to investigate eugenol's leishmanicidal activity and its mechanism of action using molecular docking to predict potential biochemical targets of eugenol in Leishmania major.

The interaction between eugenol and TNF-α/IL-12p40 was evaluated using docking methods. The leishmanicidal activities of eugenol, MA (Glucantime^®; MA), and their combination were assessed against both promastigote and amastigote stages of Leishmania major. Additionally, real-time PCR was used to measure cytokine gene expression levels in murine macrophages treated with the studied drugs.

IC₅₀ values for eugenol, MA, and their combination against L. major promastigotes were determined as 235.22 µg/mL, 298.93 µg/mL, and 159.02 µg/mL, respectively. Regarding anti-amastigote activity, the combination of eugenol with MA exhibited the lowest IC₅₀ value at 41.7 µg/mL, compared to 73.1 µg/mL for eugenol alone. The combination IC₅₀ has been located on the line that showed the additivity role. Docking studies suggest that residues within the active site of eugenol are capable of interacting with TNF-α and IL-12p40. Specifically, Leu57, Leu120, Gly120, and Gly122 were identified as common amino acids involved in binding with eugenol and TNF-α, whereas Glu12, Asn200, and His83 were associated with eugenol's interaction with IL-12p40 Gene expression analysis revealed upregulation of Th1 cytokines (IL-12P40, iNOS, IFN-γ) and downregulation of Th2 cytokines (IL-4, IL-10) in the combined treatment relative to individual treatments.

The superior efficacy of the combined treatment of eugenol and MA on L. major necessitates further research on the clinical potential of this combination in the treatment of leishmaniasis.