Enhanced Nanogel Formulation Combining the Natural Photosensitizer Curcumin and <em>Pectis brevipedunculata </em>(Asteraceae) Essential Oil for Synergistic Leishmaniasis Therapy

Neglected tropical diseases (NTDs), such as leishmaniasis, remain a global health challenge due to limited therapeutic options and rising drug resistance. In this study, we developed an advanced nanogel formulation incorporating curcumin (CUR) and Pectis brevipedunculata essential oil (OEPb) within an F127/Carbopol 974P matrix to enhance bioavailability and therapeutic efficacy against Leishmania (Leishmania) amazonensis (LLa) promastigotes. The chemical composition of OEPb was characterized using GC-MS and NMR, confirming the presence of major bioactive monoterpenes, including neral, geranial, α-pinene, and limonene. The nanogel formulation (nGPC) was optimized to ensure thermosensitivity, and stability, exhibiting a sol-gel transition at physiological temperatures. Rheological analysis revealed that nGPC exhibited Newtonian behavior at 5 ∘C, transitioning to shear-thinning and thixotropic characteristics at 25 and 32 ∘C, respectively. This behavior facilitates application and controlled drug release, making it ideal for topical formulations. Dynamic light scattering (DLS) analysis demonstrated that nGPC maintained a stable nanoscale structure with hydrodynamic diameters below 300 nm, while Fourier-transform infrared spectroscopy (FTIR) confirmed strong molecular interactions between OEPb, CUR, and the polymer matrix. Biological assays demonstrated that nGPC significantly enhanced anti-promastigote activity compared to free CUR and OEPb. At the highest tested concentration (17.5 μg/mL OEPb and 50 μg/mL CUR, nGPC induced over 88% mortality in LLa promastigotes across 24, 48, and 72 h, indicating sustained efficacy. Even at lower concentrations, nGPC retained dose-dependent activity, suggesting a synergistic effect between CUR and OEPb. These findings highlight the potential of nGPC as an innovative nanocarrier for leishmaniasis treatment. Future studies will investigate the underlying mechanisms of this synergism and explore the potential application of photodynamic therapy (PDT) to further enhance therapeutic outcomes.