Synergistic Anti-Leishmanial Activities of Morphine and Imiquimod on Leishmania infantum (MCAN/ES/98/LIM-877).

Background: This study was performed to evaluate in vitro and in vivo Leishmanicidal potential of morphine (Mph), imiquimod (IQ), and their combination.

Methods: Leishmania infantum promastigote and amastigote assays were performed at the presence of 0.015-150μM Mph, 0.04-416μM IQ, and their combination. The inhibition effects of these drugs on promastigotes were evaluated after 24, 48, and 72h. The cytotoxic effects of the drugs were evaluated by MTT as well as flow cytometry after 72h. We explored the therapeutic effects of Mph and IQ in BALB/c mice at the end of the treatment using parasite load determination and cytokine assay. One group of mice received Mph for three weeks before infection.

Results: The results of promastigote and amastigote assays showed the cytotoxic effects of the drugs at low concentrations. The cytotoxic effects were higher on promastigotes than amastigotes (p< 0.05). There was a negative correlation between drug concentration and amastigote/promastigote viability. Imiquimod alone or combined with Mph showed remarkable cytotoxic effects at all concentrations (p< 0.05). Flow cytometry results revealed apoptosis in the parasite following exposure to the drug combinations. Accordingly, the reduction of parasite loads in the spleen and liver was observed (p< 0.05) with simultaneous increases in IFN-γ and IL-4. We believe that the in vivo leishmanicidal effect was mediated by Mph through IL-4 and by IQ through both IL-4 and IFN-γ.

Conclusion: Results pointed out the promising effects of Mph and IQ at low concentrations, especially when combined.