Comparing in vitro antileishmanial activity of Scrophularia bavanatica hydroalcoholic extract against Leishmania major and Leishmania tropica promastigotes

Abstract Cutaneous leishmaniasis (CL), a neglected tropical disease, presents a significant therapeutic challenge due to the toxicity and emerging resistance of first-line drugs like Glucantime. Medicinal plants offer a promising reservoir for novel antileishmanial agents. Scrophularia bavanatica is a traditionally-used plant in Iran; yet, its efficacy against different Leishmania species remains unexplored. This study compared the in vitro antileishmanial efficacy of Scrophularia bavanatica hydroalcoholic extract (SBE) against promastigotes of Leishmania major and Leishmania tropica . Two parallel in vitro studies were conducted. Promastigotes of L. major [MRHO/IR/75/ER] and L. tropica [MHOM/IR/NADIM3] were exposed to various concentrations of SBE (0.01–100 mg/mL and 0.2–125 mg/mL, respectively) and standard Glucantime for 24, 48, and 72 hours. Parasite viability was assessed using the XTT cell proliferation assay. LC 50 values and survival percentages were calculated and statistically compared. SBE exhibited a time- and concentration-dependent antileishmanial effect against both species. However, L. tropica demonstrated significantly higher resistance. The LC 50 of SBE for L. major in the dynamic phase (47.1 µg/mL) was significantly lower than that for L. tropica , for which the LC 50 exceeded the highest tested concentration (> 125 µg/mL). A significant reduction in L. tropica promastigote survival was only observed after 72 hours of exposure (P = 0.000), whereas L. major showed significant susceptibility at 24 and 48 hours. Glucantime was effective against both species by 72 hours, but required higher concentrations for L. tropica . Scrophularia bavanatica extract possesses potent antileishmanial activity, but its efficacy is highly species-specific. L. tropica is inherently more resistant to both SBE and Glucantime compared to L. major , necessitating longer exposure times and higher doses for effective treatment. This highlights the critical importance of species identification in CL management and puts SBE forward as a promising candidate for further development against L. major .