Imipramine alters the sterol profile in Leishmania amazonensis and increases its sensitivity to miconazole

Imipramine, a tricyclic antidepressant widely used clinically, has other pharmacological effects, such as antileishmanial activity. Tricyclic antidepressants interact with lipid bilayers, and some studies have shown that imipramine inhibits methyltransferases. Leishmania spp. produces compounds with an ergostane skeleton instead of a cholesterol skeleton, and the inhibition of enzymes of the sterol biosynthesis pathway is an interesting therapeutic target. Among these enzymes, C-24 methyltransferase has been suggested to play an essential role, as its inhibition kills the parasites. In this context, we investigated whether imipramine alters the biosynthesis of sterols in L. amazonensis and evaluated the efficacy of imipramine alone and in combination with miconazole, a classical inhibitor of another step in this pathway.

To analyze the interference of imipramine with sterol metabolism, promastigotes of L. amazonensis were cultured with medium alone, 15 or 30 μM imipramine or 4 μM miconazole, and their lipids were extracted with methanol/chloroform/water (1:0.5:0.4 v/v) and analyzed by GC/MS. To assess the antileishmanial activity of the treatments, promastigotes of L. amazonensis were incubated with various concentrations of imipramine up to 100 μM and up to 24 μM miconazole. Promastigotes were also treated with the combination of imipramine and miconazole at concentrations up to 12.5 μM of imipramine and 24 μM of miconazole. Parasite growth was evaluated by the MTT assay. The fractional inhibitory concentration index (FICI) was calculated to determine whether there were synergistic effects. Peritoneal macrophages with and without L. amazonensis infection were treated with miconazole (0 - 16 μM) or imipramine (0 to 50 μM) for 72 hours. For assays of the combined treatment in amastigotes, the concentration of imipramine was fixed at 12.5 μM and various concentrations of miconazole were used up to 16 μM. The infection rate was determined by counting the infected macrophages under a light microscope.

Promastigotes treated with imipramine accumulated cholesta-5,7,22-trien-3β-ol and cholesta-7-24-dien- 3β-ol, sterols that normally increase after treatment with classical inhibitors of C-24 methyltransferase. The IC50 of miconazole in promastigotes decreased when it was used in combination with imipramine, resulting in an additive effect, with a FICI value of 0.83. Imipramine also showed activity against intracellular amastigotes and enhanced the activity of miconazole, without apparent toxicity to the host cells.

Imipramine was confirmed to have antileishmanial activity in both forms of the parasite, affecting the sterol biosynthesis of the organisms. Using imipramine in combination with azoles may be advantageous for the treatment of leishmaniasis.