Niosomal Encapsulation of Oroxylum indicum Leaf Extract for Topical Anti-Inflammatory Application

Background: Oroxylum indicum (L.) Kurz is a medicinal plant widely used in traditional Thai medicine, reported to exhibit anti-inflammatory activity. However, its topical use is limited by the poor dermal delivery of its active compounds. This study aimed to develop and characterize a topical niosomal delivery system containing O. indicum leaf extract to enhance permeation through Strat-M® membrane and anti-inflammatory activity. Methods: Extract-loaded niosomes were prepared via thin-film hydration using non-ionic surfactants and cholesterol. The developed niosomes were evaluated for their physicochemical properties, in vitro release and in vitro permeation, stability, and anti-inflammatory effects in LPS-stimulated RAW 264.7 cells. Results: The optimal formulation consisted of a phosphate buffer at pH 5.5, Span 60, cholesterol, 0.5% (w/v) extract, and 10% propylene glycol, with the extract added during the hydration step. The optimal formulation showed a high encapsulation efficiency (>70% (total phenolics) and >90% (total flavonoids), a nano-sized particle size of approximately 100–200 nm with a narrow size distribution, and a zeta potential within the acceptable value (≤−30 mV). The successful incorporation of the extract into niosome bilayers was confirmed by FTIR spectroscopy. The niosomal formulation demonstrated a significantly more sustained and controlled release of total phenolics and flavonoids, including enhanced permeation of phenolic compounds across the Strat-M® membrane, compared to the extract solution. Formulations containing 0.3–0.5% extract remained physically stable, maintaining encapsulation efficiency, particle size, and zeta potential under thermal stress conditions. Significantly, niosomes loaded with 0.5% extract exhibited the greatest inhibition of nitric oxide production in RAW 264.7 cells without cytotoxicity. Conclusions: These findings are based on in vitro membrane permeation and cell-based assays; further ex vivo or in vivo skin studies are required to confirm topical anti-inflammatory efficacy.