Comparative Investigation of the Inhibitory and Lethal Effects of Trigonelline and Glucantime Compounds on the Promastigote and Amastigote Stages of <i>Leishmania major</i>

Background and aims: The search for naturally derived pharmaceuticals with enhanced efficacy and reduced side effects for the treatment of leishmaniasis, a zoonotic infectious disease, has become a significant focus of research. This study aimed to evaluate the inhibitory and lethal effects of trigonelline, a natural alkaloid, in comparison to glucantime, a synthetic drug. Additionally, the study sought to assess the potential synergistic effects of these compounds on the promastigote and amastigote stages of Leishmania major (MRHO/IR/75/ER) under in vitro conditions. Methods: In this experimental study, L. major promastigotes and amastigotes were cultured alongside mouse macrophages (J774) and treated with the compounds under investigation. Cell viability was assessed using the trypan blue exclusion test, while metabolic activity was measured through the MTT colorimetric assay. Additionally, the inhibition of amastigotes within macrophages was evaluated using Giemsa staining. Results: Trigonelline, as a natural compound, significantly reduced the survival rate of promastigotes at concentrations of 25, 50, 100, and 200 µg/mL (P&lt;0.001). Furthermore, trigonelline enhanced the anti-leishmanial efficacy of glucantime against both the promastigote and amastigote stages at lower doses (P&lt;0.001). The cytotoxicity (CC50) for macrophages treated with glucantime was determined to be 349.1 µg/mL, while for trigonelline, it was 1863.3 µg/mL. In the case of the combination treatment, the CC50 was found to be 476.3 µg/mL. Conclusion: Trigonelline demonstrated a synergistic effect with glucantime, enhancing its anti-leishmanial activity. Given its antioxidant properties, lower cytotoxicity to macrophage cells, and potential to reduce the required dosage of glucantime in combination therapy, trigonelline represents a promising option for the treatment of leishmaniasis.