Antimicrobial Peptides and Their Anti-Leishmanial Efficacies on Leishmania tropica Promastigotes In vitro.

Objective: Antimicrobial resistance is a real threat to humanity. Pentavalent antimonials are reported non-effective in leishmaniasis treatment today, in countries like India. New treatment options have been assessed worldwide lately. Antimicrobial peptides (AMP) are the leading antibiotic candidates due to their large spectrum, fast efficacy, and low resistance risks. Cathelicidins are the AMP with well-documented antimicrobial activities against bacteria, fungi, and protozoa, over their positively charged membranes. Here, we aim to design cathelicidine-like helical peptides (CLHP), and compare their anti-Leishmanial efficacies in vitro, with meglumine antimoniate (MA) on Leishmania tropica.

Methods: A total of five study [TN-1-5] and two control (MA and non-drug) groups were formed. Cryopreserved L. tropica isolate was thawed and cultivated in Novy-MacNeal-Nicolle medium and then in RPMI. Five different CLHPs (TN1-5) were diluted in dimethyl sulphoxide. A total of 150 uL of CLHPs and MA were added into the first wells of the test plaques, followed by serial dilutions that revealed doses within 4 and 512 ug/mL. Then, 100 uL of cultures including 1x10⁸/mL of L. tropica promastigotes were added into each well. Viability of promastigotes was checked with XTT, while the parasite count was assessed at 24^th and 48^th hours.

Results: TN3 was effective at 32 ug/mL. All tested CLHPs exhibited varying degrees of anti-Leishmanial activities, except TN5, even at its highest dose.

Conclusion: TN3 showed a particular efficacy against L. tropica in vitro. Further studies including in vivo testing of the candidate's both efficacy and toxicity are essential.