Formulation and evaluation of amphotericin B emulsion gel against Leishmania major in a murine model: parasite burden, gene expression, and histopathological profiling

Cutaneous leishmaniasis (CL) is the most prevalent form, with increasing incidence linked to factors such as drug resistance, HIV co-infection, and lack of effective vaccines. Amphotericin B (AmB) is an effective antileishmanial drug; however, its clinical use is limited by nephrotoxicity, high cost, and the requirement for parenteral administration. Therefore, there is a need for safer, non-invasive topical formulations with improved efficacy and reduced systemic toxicity. This study aimed to develop and evaluate a novel Amphotericin B-loaded nanoemulsion gel (AmB-NEG) for the topical treatment of Leishmania major infection in mice. AmB was incorporated into a Carbomer 940-based nanoemulsion gel, and its physicochemical properties, including pH, stability, and particle size, were characterized. In vivo efficacy was assessed in BALB/c mice infected with L. major. Lesion size, splenic parasite burden (by qPCR), histopathological changes, and cytokine gene expression (IFN-γ, IL-12, IL-4, and IL-10) were evaluated. The optimized AmB-NEG exhibited uniform nanodroplets (< 50 nm), excellent stability, and a near-neutral pH suitable for dermal application. Topical AmB-NEG significantly reduced lesion size and splenic parasite burden compared with both untreated and conventional AmB-treated groups (P < 0.01). Histopathological analysis revealed reduced inflammation and parasite density, while qRT-PCR confirmed upregulation of Th1 cytokines (IFN-γ, IL-12) and downregulation of Th2 cytokines (IL-4, IL-10). The developed AmB-NEG demonstrated enhanced therapeutic efficacy and immunomodulatory activity against cutaneous leishmaniasis while minimizing systemic toxicity. This topical nanoformulation offers a promising, patient-friendly alternative to conventional AmB therapy and warrants further preclinical and clinical evaluation.